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Computer Systems

the presentation supporting the Computer Systems presentation of the Scottish Qualifications Authority's Higher Grade.

the presentation supporting the Computer Systems presentation of the Scottish Qualifications Authority's Higher Grade.

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Computer Systems

1. 1. Outcome 1 - Contents <ul><li>1 Data Representation </li></ul><ul><li>2 Computer Structure </li></ul><ul><li>3 Computer Performance </li></ul><ul><li>4 Peripherals </li></ul><ul><li>5 Networking </li></ul><ul><li>6 Using Networks </li></ul><ul><li>7 Computer Software </li></ul><ul><li>8 Supporting Software </li></ul>
2. 2. 1 Data Representation 1.1 Introduction <ul><li>Lowest level in computer only binary numbers can be used. </li></ul><ul><li>We work in base 10. </li></ul><ul><li>Computer must be able to process +ive and –ive, very large and very small numbers. </li></ul><ul><li>We look at how the computer uses numbers to represent text and graphics </li></ul>
3. 3. 1 Data Representation 1.2.1 Decimal Numbers <ul><li>We use base 10 </li></ul><ul><li>When expressing large numbers in terms of powers of 10 the following abbreviations are used: </li></ul><ul><li>10 1 = 10 </li></ul><ul><li>10 2 = 100 </li></ul><ul><li>10 3 = 1000 = 1 kilo </li></ul><ul><li>10 6 = 1,000,000 = 1 Mega </li></ul><ul><li>10 9 = 1,000,000,000 = 1 Giga </li></ul><ul><li>10 12 = 1,000,000,000,000 = 1 Tera </li></ul>
4. 4. 1 Data Representation 1.2.1 BinaryNumbers Computers work in number base 2 which uses 2 symbols, 0 and 1 to represent a value. In computing systems, large numbers are expressed in terms of powers of 2 and use the following abbreviations: 2 1 has a decimal equivalent of 2 2 2 has a decimal equivalent of 4 2 3 has a decimal equivalent of 8 2 4 has a decimal equivalent of 16 2 5 has a decimal equivalent of 32 2 6 has a decimal equivalent of 64 2 7 has a decimal equivalent of 128 2 8 has a decimal equivalent of 256 2 9 has a decimal equivalent of 512 2 10 has a decimal equivalent of 1024 and is abbreviated to 1 kilo 2 20 has a decimal equivalent of 1,048,576 and is abbreviated to 1 Mega 2 30 has a decimal equivalent of 1,073,741,824 and is abbreviated to 1 Giga 2 40 has a decimal equivalent of 1,099,511,627,776 and is abbreviated to 1 Tera
5. 5. 1 Data Representation 1.2.2 Decimal to Binary <ul><ul><ul><li>How to convert decimal to binary e.g. 29 </li></ul></ul></ul>Giving 11101 <ul><li>Using 1 byte for storage gives 256 possible numbers. </li></ul><ul><li>2 byte gives 65536, 0-65535 </li></ul><ul><li>Increasing the size of the storage for numeric data increases the range of numbers which can be stored. </li></ul>R1 0 2 R1 1 2 R1 3 2 R0 7 2 R1 14 2 29 2
6. 6. 1 Data Representation 1.2.3 Binary to Decimal <ul><ul><li>Numbers converted to binary – number base 2 </li></ul></ul><ul><ul><li>Example of 154 represented as a binary number </li></ul></ul>=154 +0 +2 +0 +8 +16 +0 +0 128 0 1 0 1 1 0 0 1 1 2 4 8 16 32 64 128
7. 7. 1 Data Representation 1.2.4 Hexadecimal Long binary numbers can be difficult to read correctly. Computers have memory addresses of 2 or 4 bytes long which give addresses of 16 or 32 bits. Hexadecimal is base 16 and organises the bits into groups of four. The conversion between base 2 and base 16 is very simple. Hex needs the digits 0-9 and letters A-F. E.g. 11010100010110010011001010010110 becomes 1101 0100 0101 1001 0011 0010 1001 0110 which in Hex is D459 3256
8. 8. 1 Data Representation 1.2.5 Why Binary <ul><li>Logic circuits based on two state logic – use only 0 and 1. </li></ul><ul><li>We only need two voltages 0 and a voltage of any value = 1 </li></ul><ul><li>There are only 4 rules of arithmetic with binary (100 in base 10). </li></ul><ul><li>Robust – can cope with degradation of signal. </li></ul>
9. 9. Data Representation 1.2.6 & 1.2.7 Integers <ul><li>Positive numbers </li></ul><ul><ul><li>Converted directly to binary </li></ul></ul><ul><ul><li>2 bytes = 16 bits gives 0 to 2 16 -1 or 0 to 65535 </li></ul></ul><ul><ul><li>n bytes gives n*8 bits - 2 n*8 - 1 </li></ul></ul><ul><li>Negative Numbers </li></ul><ul><ul><li>2 16 : Same range but –32768 to 32767 </li></ul></ul><ul><ul><li>Using sign bit 0 +ive and 1 –ive e.g. 011 = 3 and 111 = -3 </li></ul></ul><ul><ul><ul><li>Sign and magnitude does not work because: </li></ul></ul></ul><ul><ul><ul><li>Addition does not work properly (-5+-10 gives 15) </li></ul></ul></ul><ul><ul><ul><li>Two 0’s (00000000 and 10000000) </li></ul></ul></ul>
10. 10. Data Representation 1.2.8 Twos Complement <ul><ul><li>Two’s Complement is another way of representing negative numbers. </li></ul></ul><ul><ul><li>Addition works and there is only one zero </li></ul></ul><ul><ul><li>All 0’s are converted to 1’s and 1’s to 0’s then 1 is added. </li></ul></ul><ul><ul><li>To convert 5 to –5 </li></ul></ul>OR 5 OR -5 0 +1 1 0 1 1 1 1 1 1 1 0 1 1 1 1 1 1 0 1 0 0 0 0 0
11. 11. Data Representation 1.2.9 Real Numbers <ul><li>Real numbers are stored as floating point or scientific notation. Numbers stored as base and exponent. </li></ul><ul><li>E.g 34008.6 is .340086*10 5 </li></ul><ul><li>In binary 1101.1001 is .11011001*2 100 (the 4is 100 in binary) </li></ul><ul><li>The mantissa is 11011001 and the exponent is 100 </li></ul><ul><li>Usually 4 bytes used for mantissa and 2 for exponent </li></ul><ul><li>Increasing the size of the mantissa increases accuracy </li></ul><ul><li>Increasing the size of the exponent increases the range of numbers which can be stored </li></ul>
12. 12. 1 Data Representation 1.3 Text <ul><li>ASCII </li></ul><ul><ul><li>Each character is stored in an 8 bit binary code called the ASCII system. </li></ul></ul><ul><ul><li>E.g. A is stored as 65 (01000001 in Binary). </li></ul></ul><ul><ul><li>1 byte can store 256 different characters – enough for all the keys on the keyboard and several foreign symbols (for currency etc.). </li></ul></ul><ul><li>Unicode </li></ul><ul><ul><li>Need to represent non-Latin chars e.g. Japanese and Chinese </li></ul></ul><ul><ul><li>Characters encoded using 16 bits – 65,536 symbols. </li></ul></ul><ul><ul><li>MS Office stores documents in Unicode </li></ul></ul>
13. 13. Data Representation 1.4 Graphics Most displays use Raster graphics – same as TV. Displays store images as a matrix of pixels in the refresh buffer. Separate images now stored in VRAM (Video RAM). VRAM represents the entire screen area and the term bit map is used to describe the one-to-one mapping of pixels in VRAM to pixels on the screen.
14. 14. Data Representation 1.4.1 Bit-mapped Graphics <ul><li>For a graphic drawn in a painting package the computer stores the data as a 2 dimensional array of pixels. </li></ul><ul><li>Each pixel in a black and white image is 1 bit in memory. </li></ul><ul><li>2 bits can store 4 colours or shades of grey. </li></ul><ul><li>8 bits can store 256 colours. </li></ul><ul><li>The number of bits used for each pixel is the bit depth. </li></ul><ul><li>The resolution is the number of pixels in the height and width of the image. </li></ul><ul><li>Bit mapped images are often generated from scanned pictures and can create huge files. </li></ul><ul><li>Editing can be performed at pixel level. </li></ul><ul><li>When images are enlarged they can become “lumpy” and lose definition. </li></ul>
15. 15. Data Representation 1.4.2 Calculating Memory Requirements <ul><li>We need to know the size of the image, resolution and bit depth. </li></ul><ul><ul><li>Size – usually inches e.g. 6” x 4” </li></ul></ul><ul><ul><li>Resolution – say 500 dpi (pixels per inch) </li></ul></ul><ul><ul><li>Bit Depth – e.g. 1 bytes for 256 colours </li></ul></ul>No of bytes is 6,000,000 bytes / 1024 = 5859K = 5.7 MB 24 x 250,000 = 6,000,000 4 x 500 6 x 500 * Bit depth Total Pixels Pixels down Pixels Across
16. 16. Data Representation 1.4.3 Arranging The Bytes <ul><li>There are many different ways of arranging the bytes that hold image information, but one way is to map them so that the first byte represents the top left pixels, the second byte represents the pixels to the right of the first pixel, until the end of the first row is reached, when the next byte holds the information for the left hand end of the second row. For a small (24 pixel by 4 rows ) display the layout would look like this: </li></ul>The image is saved as a series of bytes to a storage device, such as memory or disk.If we wish to review the image then it is a simple matter to transfer the image data back into the video memory as a direct copy. As this image is also in a bit mapped format, we can still move it to and from other storage devices without any translation.
17. 17. Data Representation 1.4.4 Greyscale A rudimentary greyscale effect provides a ’black’, ’white’ and two levels of ’grey’. As this comprises four different values we need two bits to represent each pixel (00 for black, 01 for darker grey, 10 for lighter grey and 11 for white ). As each pixel now requires twice as many bits, we will require twice as much memory for a given screen size as a black and white image. We can provide more levels of grey by allocating more bits to each pixel. By the time we have eight bits (one byte) to one pixel we can represent 256 different intensities. Monochrome displays are often clearer, especially for text than colour display. The requirement to use colour for such items as colour pictures and user interface issues, dictates that colour displays are more likely to be purchased.
18. 18. Data Representation 1.4.6 Compression <ul><li>A colour bit – mapped image with a high resolution and 24 bit colour needs a lot of storage (50MB for a smallish photo). </li></ul><ul><li>File compression is used to reduce storage requirements. </li></ul><ul><li>Different techniques – coding using and index of colours actually used and not coding differences indistinguishable to the human eye. </li></ul>
19. 19. Data Representation 1.4.5 Colour One colour can be represented by one byte giving 256 colours (GIF format). Monitors etc. have 3 primary (additive) colours, Red, Blue and Green. Other colours obtained from adding light. We use 8 bits for Red, 8 for Blue and 8 for Green which give us 256 x 256 x256 colours – over 16 million. We need 3 bytes to describe RGB coded colours. Codes can be used by a programmer to describe colours in Hex code.
20. 20. Data Representation 1.4.7 Vector Graphics <ul><li>Objects not described pixel by pixel but by its attributes (start & end positions, thickness & colour of lines etc.) </li></ul><ul><li>Sometimes called object-orientated graphics. </li></ul><ul><li>Vector graphics are resolution independent . Rasterisation need for conversion to bit map for display or printing. </li></ul><ul><li>Editing at pixel level not possible. </li></ul><ul><li>Can be scaled without losing original image quality </li></ul><ul><li>Less storage required </li></ul><ul><li>Can be grouped and edited at the object level. </li></ul><ul><li>Can be placed over another graphic without rubbing it out as happens with bit-mapped. </li></ul>
21. 21. 2 Computer Structure 2.1 An Introduction This unit on Computer Structure describes in detail the function of the component parts of a processor in the manipulation of data. This is extended to the methods of transferring data within a processor and between a processor and memory. The concept of a stored program is considered and the steps in the fetch-execute cycle to access and run programs. Memory types are considered, from registers to backing storage and how memory is defined and addressed.
22. 22. 2 Computer Structure 2.2 Computer Organisation <ul><li>Computers play a significant role in meeting our everyday requirements. You can now browse the Internet for: </li></ul><ul><li>a new home, </li></ul><ul><li>Shop on-line and have home delivery </li></ul><ul><li>import a new car from abroad </li></ul><ul><li>order clothes from a catalogue company </li></ul><ul><li>communicate with friends overseas. </li></ul><ul><li>The ways in which you learn are also changing. </li></ul><ul><li>On-line homework </li></ul><ul><li>Computer based learning tools </li></ul>
23. 23. 2 Computer Structure 2.2 Computer Organisation <ul><li>It makes sense to find out how they work and how you can make use of them. </li></ul><ul><li>How are they structured? </li></ul><ul><li>How do they operate? </li></ul><ul><li>How is data represented? </li></ul><ul><li>Why are some computers more powerful than others? </li></ul><ul><li>What devices can you attach? </li></ul><ul><li>How do they communicate? </li></ul><ul><li>Answers can be found in the following Topic </li></ul>
24. 24. 2 Computer Structure 2.2. Calculating Machines- From Babbage to VLSI <ul><li>Abacus developed about 1300 AD by Chinese </li></ul><ul><li>Logarithms developed by John Napier </li></ul><ul><li>Other manual devices developed by Pascal & Liebniz </li></ul><ul><li>First mechanical calculator developed by Charles Babbage (1792 – 1871) Difference Engine and then Analytical Engine. </li></ul><ul><li>Idea of stored program concept developed. </li></ul><ul><li>First Electrical machine Enigma codebreaker in WW2. </li></ul><ul><li>Vacuum tubes (40’s replaced by transistors (60’s) </li></ul><ul><li>From 1965 to present circuitry all on one chip Integrated circuits. </li></ul><ul><li>Now we have VLSI (Very large Scale Integration) </li></ul>
25. 25. 2 Computer Structure 2.2.1 A Two State Machine <ul><li>Typical 4 box diagram </li></ul><ul><li>Only 2 states used in all components and data storage, on or off, 1 or 0. </li></ul><ul><li>Advantages of 2 state. </li></ul><ul><ul><li>Simplicity – 2 voltage levels. </li></ul></ul><ul><ul><li>Good tolerance </li></ul></ul><ul><ul><li>Simple calculations. </li></ul></ul>Input Processor Memory RAM & ROM Output Backing Storage CPU
26. 26. 2 Computer Structure 2.2.2.1 The structure of the CPU (a) Memory Processor Control unit ALU Registers, A, MAR, MDR, PC, SP Address bus – 1 way Data bus – 2 way Control Bus Internal buses
27. 27. 2 Computer Structure 2.2.2.1 The structure of the CPU (b) <ul><li>ALU (Arithmetic & Logic Unit) </li></ul><ul><ul><li>Data is processed and manipulated. </li></ul></ul><ul><ul><li>Involves arithmetic operations and logical comparisons. </li></ul></ul><ul><li>Control Unit </li></ul><ul><ul><li>Manages execution of instructions. </li></ul></ul><ul><ul><li>Sends control signals around the computer. </li></ul></ul><ul><li>Registers </li></ul><ul><ul><li>Storage location with the CPU </li></ul></ul><ul><ul><li>Hold calculations, store addresses etc. </li></ul></ul><ul><li>Main Memory </li></ul><ul><li>External Memory </li></ul><ul><li>Peripheral Devices </li></ul>
28. 28. 2 Computer Structure 2.2.3 The stored program concept All computers based on same basic design, known as the Von Neumann Architecture . Computers carry out tasks by executing machine instructions. A series of these instructions is called a machine code program held in main memory as a stored program , a concept first proposed by John Von Neumann in 1945. Central Processing Unit (CPU) fetches, decodes and executes the machine instructions. By altering the stored program it is possible to have the computer carry out a different task.
29. 29. 2 Computer Structure 2.2.4 The fetch execute cycle To execute a machine code program it must first be loaded, together with any data that it needs, into main memory (RAM). Once loaded, it is accessible to the CPU which fetches one instruction at a time, decodes and executes it at electronic speed. Fetch, decode and execute are repeated until a program instruction to HALT is encountered. This is known as the fetch-execute cycle .
30. 30. 2 Computer Structure 2.2.4.1 The fetch execute cycle in detail <ul><li>This is how the: </li></ul><ul><li>Address bus </li></ul><ul><li>Data bus </li></ul><ul><li>Control Bus </li></ul><ul><li>Registers </li></ul><ul><li>All take part in reading an instruction from memory and executing it. </li></ul>
31. 31. 2 Computer Structure 2.2.4.3 The fetch phase <ul><li>. </li></ul>1. The contents of the PC are copied into the MAR; 2. The contents of memory at the location designated by the MAR are copied into the MDR; 3. The PC is incremented; 4. The contents of the MDR are copied into the IR. 2.2.4.4 The Execute phase 1. Decode the instruction in the IR; 2. Execute the instruction in the IR.
32. 32. 2 Computer Structure 2.2.8 Computer Components and Their Function The components of the CPU and the connections to devices that are external to it are shown.
33. 33. 2 Computer Structure 2.3 Memory Main memory (RAM and ROM) stores programs and data while the computer is operating. <ul><li>Any location in memory can be read from or written to by referring to its address. </li></ul><ul><li>Memory can be organised as: </li></ul><ul><li>8- bit wide (PC-8088) </li></ul><ul><li>16-bit wide (XT-8086, AT-80286) </li></ul><ul><li>32-bit wide (386DX, 486SX, 486DX) </li></ul><ul><li>64-bit wide (Pentium) </li></ul>
34. 34. 2 Computer Structure 2.3.1 RAM <ul><li>RAM </li></ul><ul><ul><ul><li>Has same access time for all locations. </li></ul></ul></ul><ul><ul><ul><li>Volatile – loses contents on power off. </li></ul></ul></ul><ul><ul><li>2 Types of RAM Static and Dynamic </li></ul></ul><ul><ul><ul><li>Static – holds contents as long as there is power. </li></ul></ul></ul><ul><ul><ul><li>Dynamic – has to be refreshed (every 2 ms). </li></ul></ul></ul><ul><li>Each memory location has a unique address . </li></ul>
35. 35. 2 Computer Structure 2.3.2 ROM <ul><li>ROM </li></ul><ul><ul><ul><li>Contents permanent or non-volatile. </li></ul></ul></ul><ul><ul><ul><li>Software & data fixed into ROM at manufacture. </li></ul></ul></ul><ul><ul><ul><li>Operating systems and specialised ROMs (e.g. cameras and CD players etc.). </li></ul></ul></ul><ul><ul><li>Some ROMs can be reprogrammed </li></ul></ul><ul><ul><ul><li>EPROM – electrically programmable read only memory (data erased by ultraviolet light and new program burned onto ROM </li></ul></ul></ul><ul><ul><ul><li>EEPROM – electrically erasable programmable read only memory – selective parts can be reprogrammed & used in developmental work </li></ul></ul></ul>
36. 36. 2 Computer Structure 2.3.4 Cache Memory <ul><li>Faster processors mean data is being processed before the next instructions can be read from memory (system busses slow). </li></ul><ul><li>Most systems have 2 nd smaller area of fast SRAM. Next instructions read into cache – much faster than RAM. </li></ul>
37. 37. 2 Computer Structure 2.3.6 External Memory <ul><li>External memory , such as the hard disk, holds quantities of data too large to store in main memory. </li></ul><ul><li>It is also used to keep a permanent copy of programs and data. </li></ul><ul><li>Examples of external memory devices are: </li></ul><ul><li>hard disk; </li></ul><ul><li>floppy disk; </li></ul><ul><li>zip disk; </li></ul><ul><li>CD-R; </li></ul><ul><li>magnetic tape; </li></ul><ul><li>flash drive. </li></ul>
38. 38. 2 Computer Structure 2.4 Central Processing Unit Central Processing Unit. The CPU coordinates and controls the activities of all other units in the computer system. It executes program instructions and manipulates data in accordance with the instructions. It uses a standard architecture composed of the following three components: Arithmetic and logic unit (ALU); Control unit; Registers. All three components work together to form the processor.
39. 39. 2 Computer Structure 2.4.1 Architecture of the microprocessor We will now study the internal architecture of the microprocessor (CPU) itself. Because of the stored program concept , we must consider the relationship between the CPU and memory. This is a diagram of a fairly typical microprocessor design, showing the internal structure of the CPU and its relationship to the memory of the computer.
40. 40. 2 Computer Structure 2.4.2 Accessing Memory The CPU has to access memory both for instructions and to receive and transmit data from or to memory. Memory Address Register (MAR) - specifies the address in memory for the next read or write operation from or to memory; The Memory Data Register (MDR) or Memory Buffer Register (MBR) - contains the data to be written to memory or receives the data read from memory. <ul><li>MAR register connected to the address bus </li></ul><ul><li>MDR register connected to the data bus. </li></ul>
41. 41. 2 Computer Structure 2.4.2 Accessing Memory (2) To read data from memory , CPU places the address of the memory location into the MAR and activates the memory-read control line of the system bus. This will cause the required data to be transmitted from memory via the data bus to the MDR; To write from the CPU to memory , the CPU places the data to be written in theMDR; the address of the memory location where they are to be written is placed in the MAR; and the memory-write control line is activated. The MAR and MDR registers have a large part to play in the fetch-execute cycle.
42. 42. 2 Computer Structure 2.4.3 Functions of Control Bus <ul><li>Control bus has several lines, used singly to initiate a process. </li></ul><ul><ul><ul><li>Read Line – initiates memory read operation. </li></ul></ul></ul><ul><ul><ul><li>Write Line - initiates memory write operation. </li></ul></ul></ul><ul><ul><ul><li>Clock – Generates pulse to synchronise components. </li></ul></ul></ul><ul><ul><ul><li>Interrupt – Signal to processor of an interrupt like a key press or mouse click. Processor saves stack and deals with the interrupt. </li></ul></ul></ul><ul><ul><ul><li>NMI – Non-Maskable Interrupt. Interrupt which cannot be ignored. </li></ul></ul></ul><ul><ul><ul><li>Reset – Clears all registers, aborts program and gives control back to the operating system. </li></ul></ul></ul>
43. 43. <ul><li>Polling </li></ul><ul><ul><li>The processor checks each part of the system in turn and if any part wants the processors attention it signals to the processor. </li></ul></ul><ul><li>Interrupts </li></ul><ul><ul><li>This is how a PC works. When a key is pressed or mouse clicked an interrupt is generated and the processor carries out that task (sometimes it is “doing nothing” and is interrupted. </li></ul></ul><ul><ul><li>Some interrupts need not be actioned (Maskable Interrupts), others must be actioned (NMI) e.g Ctrl+Alt+Del </li></ul></ul>2 Computer Structure 2.4.3.1 Getting the processors attention
44. 44. 2 Computer Structure 2.4.4 The Arithmetic Logic Unit <ul><li>ALU </li></ul><ul><ul><li>Where data is processed and manipulated. </li></ul></ul><ul><ul><li>ALU involves arithmetic operations and logical operations . </li></ul></ul><ul><ul><li>ALU uses temporary registers to hold data. </li></ul></ul><ul><ul><li>Accumulator is main register. </li></ul></ul>
45. 45. 2 Computer Structure 2.4.5 Registers <ul><li>memory address register (MAR) holds address of a location in main memory. </li></ul><ul><li>memory buffer register (MBR) holds data that has just been read from main memory or is to be written to main memory. </li></ul><ul><li>instruction register (IR) holds the current instruction that is being executed. </li></ul><ul><li>program counter (PC) holds the address of the next instruction to be fetched from memory. </li></ul><ul><li>Processor also has a set of general purpose registers . They are called general purpose because their role is not defined at manufacture and can be used by programmers as appropriate. </li></ul>
46. 46. 2 Computer Structure 2.5 Buses <ul><li>Data is transferred between memory and processor by buses. </li></ul><ul><li>Address Bus </li></ul><ul><ul><li>Pinpoint memory location. </li></ul></ul><ul><ul><li>One-way Bus </li></ul></ul><ul><li>Data Bus </li></ul><ul><ul><li>Transfers the data </li></ul></ul><ul><ul><li>Same size as Word size </li></ul></ul><ul><ul><li>Two-way Bus </li></ul></ul><ul><li>Control Bus </li></ul><ul><ul><li>Initiates and controls operations. </li></ul></ul><ul><li>Inside the processor. </li></ul>Memory Processor Address Bus Data Bus Control Unit Control Bus
47. 47. 2 Computer Structure 2.5.1 Addressability <ul><li>The Word Length is the size of data, in bits, which can be manipulated as a single unit by the processor. </li></ul><ul><li>In an ideal computer the size of the data pathways and the size of memory locations will match. </li></ul><ul><li>Address bus determines amount of addressable memory </li></ul><ul><ul><li>8 bit address bus can access 2 8 = 256 locations </li></ul></ul><ul><ul><li>16 bit address bus can access 2 16 = 65,536 locations (64K) </li></ul></ul><ul><ul><li>24 bit address bus can access 2 24 = 1,677,216 locations (16MB) </li></ul></ul><ul><ul><li>32 bit address bus can access 2 32 = 4294967296 locations (4GB) </li></ul></ul><ul><ul><li>If we have 2 bytes or 4bytes for each memory location we get for a 24 bit bus 16MB of addressable locations, but 32MB or 64MB of actual storage. </li></ul></ul>
48. 48. 3 Computer Performance 3.2 Measuring Performance <ul><li>When we measure performance we usually mean how fast the computer carries out instructions. The measure we use is MIPS, millions of instructions per second. </li></ul><ul><li>MIPS affected by </li></ul><ul><ul><li>The clock speed of the processor </li></ul></ul><ul><ul><li>The speed of the buses </li></ul></ul><ul><ul><li>The speed of memory access. </li></ul></ul>
49. 49. 3 Computer Performance 3.2.1 The Clock <ul><li>Every processor has a clock which ticks continuously at a regular rate. </li></ul><ul><li>Synchronises all the components. </li></ul><ul><li>Cycle time measured in MHz or GHz </li></ul><ul><li>200 MHz (megahertz) means the clock ticks 200,000,000 times a second (P1 -1995) </li></ul><ul><li>1.4 GHz (gigahertz) is 1,400,000,000 times a second (P4 – 2001) </li></ul><ul><li>2.3 – 4+ GHz on P5 in 2004 </li></ul>
50. 50. 3 Computer Performance 3. 2 Measures of Processor Speed <ul><li>Clock Speed </li></ul><ul><ul><li>Generally the faster the clock speed the faster the processor – 3.2 GHz is faster than 933 MHz </li></ul></ul><ul><li>Mips – Millions of Instructions per Second </li></ul><ul><ul><li>Better comparison but beware of false claims e.g. only using the simplest & fastest instructions and different processor families. </li></ul></ul><ul><li>Flops – Floating Point Operations per sec. </li></ul><ul><ul><li>Best measure as FP operations are in every processor and provide best basis. </li></ul></ul><ul><li>Benchmark Tests </li></ul><ul><ul><li>Well defined standardised routine to test the performance of a computer. </li></ul></ul><ul><ul><ul><li>Dhrystone – tests string and frequently used functions </li></ul></ul></ul><ul><ul><ul><li>Whetstone – test using arithmetic functions </li></ul></ul></ul>
51. 51. 3 Computer Performance 3.3.1 Data Bus Width <ul><li>A WORD is the basic number of bits a processor can handle in one operation. </li></ul><ul><ul><li>If word size and data bus same size then data transfers carried out in single operation. </li></ul></ul><ul><li>Width of data bus defines how much data can be carried in one fetch. </li></ul><ul><ul><li>32 bit data bus (word length) carries twice as much data as a 16 bit bus and a 32 bit system should be faster. </li></ul></ul><ul><ul><li>Most modern processor 32 bit but some AMD 64 bit. </li></ul></ul><ul><li>Width of Address bus affects the amount of memory which can be accessed. </li></ul>
52. 52. 3 Computer Performance 3.3.2 Peripherals & System Performance <ul><li>Peripherals work at much slower speeds than the CPU. </li></ul><ul><ul><li>Buffers and spooling can help. </li></ul></ul><ul><ul><li>Sound cards can have their own processor, RAM and ROM. </li></ul></ul><ul><ul><li>Video cards their own RAM (up to 256Mb) </li></ul></ul>
53. 53. 3 Computer Performance 3.3.2 Interfaces & Input/output Devices <ul><li>An interface makes the link between the processor and a peripheral (disk drive, printer etc.). </li></ul><ul><li>Peripherals work at different speeds, use different formats. </li></ul><ul><li>Parallel to serial conversion is often needed </li></ul><ul><ul><li>Some devices are serial – 1 bit at a time is transferred. Serial used for long (over 2m) distances. </li></ul></ul><ul><ul><li>Some are parallel (printers) – 8 bits at a time. Used for short distances problems with skewing – loss of data integrity. </li></ul></ul><ul><li>Interface transfers data so the processor is delayed as little as possible. It has buffers to store blocks of data in transit. </li></ul><ul><li>Memory mapped I/O uses memory linked to peripheral. </li></ul><ul><li>Spool files are used when large quantities of data are sent to a slow peripheral, like a printer. Enables background printing . </li></ul>
54. 54. 3 Computer Performance 3.3 Memory & System Performance <ul><li>Speed of access & Word size </li></ul><ul><ul><li>15-120 nanosecond but memory speed and word size dictated by motherboard and processor </li></ul></ul><ul><li>Amount of memory </li></ul><ul><ul><li>Adding memory (upgrade) usually improves system performance esp. graphics & multimedia. </li></ul></ul><ul><ul><li>Usually 2 slots on motherboard so max memory is 2 x largest modules (currently 512MB largest affordable. </li></ul></ul><ul><li>Cache (pronounced cash ) memory </li></ul><ul><ul><li>Cache exists between memory and processor </li></ul></ul><ul><ul><li>Very fast memory speeding data transfer in shorter fetch cycle. </li></ul></ul>
55. 55. 4 Peripherals 4.1 Introduction <ul><li>Examine a range of hardware devices which carry out typical talks. </li></ul><ul><li>We will examine devices in terms of:- </li></ul><ul><ul><li>Speed </li></ul></ul><ul><ul><li>Cost </li></ul></ul><ul><ul><li>Resolution </li></ul></ul><ul><ul><li>Compatibility </li></ul></ul><ul><li>Developments and trends in storage devices </li></ul><ul><li>Serial & parallel interfaces and wireless communications </li></ul>
56. 56. 4.2 – Input & Output Devices 4.2.1 Keyboards <ul><li>QWERTY keyboard </li></ul><ul><ul><li>has its roots in mechanical typewriters – to slow down operators to avoid jamming the keys. </li></ul></ul><ul><ul><li>Key press causes a scan code to be sent to the computer. </li></ul></ul><ul><ul><ul><li>Sent via serial coble to keyboard controller. </li></ul></ul></ul><ul><ul><ul><li>Sent as ASCII Codes </li></ul></ul></ul><ul><li>Modified Keyboards </li></ul><ul><ul><li>Used to alleviate Repetitive Strain Injury (RSI) </li></ul></ul><ul><ul><li>Customised keypads can have more (or fewer) keys all programmable to suit particular situations. </li></ul></ul><ul><ul><li>Adjustable split keyboard in 3 parts to allow flexibility. </li></ul></ul>
57. 57. 4.2 – Input & Output Devices 4.2.2 Scanners <ul><li>Scanners </li></ul><ul><ul><li>Flat bed scanner allows for up to A4 size documents </li></ul></ul><ul><ul><ul><li>Document placed face downwards on glass panel and scanned. </li></ul></ul></ul><ul><ul><ul><li>Light beam reflects light from the document and photocells measure the light reflected. </li></ul></ul></ul><ul><ul><ul><li>Analogue data needs converted to digital (A DC) </li></ul></ul></ul><ul><ul><li>Modern scanners use high bit depths to allow high resolutions. </li></ul></ul><ul><ul><li>Images must be matched to their purpose </li></ul></ul><ul><ul><ul><li>No point in scanning at a resolution of more than 75 dpi for a screen based display. </li></ul></ul></ul><ul><ul><ul><li>No point in scanning at 600 dpi for a printer rated at 300 dpi. </li></ul></ul></ul>
58. 58. 4.2 – Input & Output Devices 4.2.2 Scanners <ul><li>Accuracy – measured by how close the image is to the original. </li></ul><ul><ul><li>Resolution is the dots per inch (dpi) that can be detected by the scanner hardware. A 600 dpi scanner has 600 photocells per linear inch. </li></ul></ul><ul><ul><li>Bit depth usually 24 bits (8 red, 8 green, 8 blue). </li></ul></ul><ul><li>Capacity </li></ul><ul><ul><li>Little internal buffering, rely on techniques to transfer the data. </li></ul></ul><ul><ul><li>Storage can be high e.g. A4 page at 600 dpi requires 33.28MB for 8 bit and around 100MB for full colour. </li></ul></ul><ul><li>Cost </li></ul><ul><ul><li>Dropped dramatically in recent years </li></ul></ul><ul><ul><li>Bundled software often the major selling point. </li></ul></ul>
59. 59. 4.2 – Input & Output Devices 4.2.3 Sound <ul><li>Naturally Occurring Sound </li></ul><ul><ul><li>Natural sound is analogue in form </li></ul></ul><ul><ul><li>To input sound to a computer </li></ul></ul><ul><ul><ul><li>Software samples the incoming signal </li></ul></ul></ul><ul><ul><ul><li>Coverts the signal into digital form </li></ul></ul></ul><ul><ul><ul><li>Usually compresses the file </li></ul></ul></ul><ul><ul><li>This is called ADC – Analogue to Digital Conversion </li></ul></ul><ul><ul><li>Simplest input device is a microphone with sound card but sound files can be taken from a CD and downloaded from the Internet. </li></ul></ul><ul><ul><li>Sound card performs the ADC and compression </li></ul></ul>
60. 60. 4.2 – Input & Output Devices 4.2.3 Sound sampling <ul><li>Sampling </li></ul>Sampler listens to sound repeatedly and stores a number representing the amplitude each time <ul><li>Sampling Rate </li></ul><ul><ul><li>No of times per second sampler listens to the sound e.g. 22 kHz is 22,000 times a second </li></ul></ul><ul><li>Sample Size </li></ul><ul><ul><li>No of bits stored per sample e.g. 8 or 16 bit samples </li></ul></ul><ul><li>Compression </li></ul><ul><ul><li>Reduce storage space and reduce quality </li></ul></ul>
61. 61. 4.2 – Input & Output Devices 4.2.3 Sound <ul><li>Accuracy </li></ul><ul><ul><li>Resolution – Three sampling resolutions in common use. </li></ul></ul><ul><ul><ul><li>11.025 KHz (8-bit) – voice quality </li></ul></ul></ul><ul><ul><ul><li>22.05 KHz (8-bit) – Quality of AM radio </li></ul></ul></ul><ul><ul><ul><li>44.1 KHz (16-bit) – CD quality stereo [data sampled 44,100 times per second] </li></ul></ul></ul><ul><ul><li>Bit-Depth </li></ul></ul><ul><ul><ul><li>8-bit sample size can hold 256 amplitudes per sample </li></ul></ul></ul><ul><ul><ul><li>16-bit sample size can hold 65,536 amplitudes per sample </li></ul></ul></ul><ul><li>Capacity </li></ul><ul><ul><li>No built-in cache. Depends on fast access via the sound card to hard disk storage. 10.09MB to store 2 mins stereo audio. </li></ul></ul><ul><ul><li>Compression required e.g. reduce sample rate / size or use a compression technique to reduce file size. </li></ul></ul>
62. 62. 4.2 – Input & Output Devices 4.2.4 Video <ul><li>Video Digitising </li></ul><ul><ul><li>is performed by special video digitising circuitry installed on the motherboard of the computer. </li></ul></ul><ul><ul><li>File Formats </li></ul></ul><ul><ul><ul><li>Quick Time </li></ul></ul></ul><ul><ul><ul><li>MPEG </li></ul></ul></ul><ul><ul><ul><li>AVi </li></ul></ul></ul>
63. 63. 4.2 – Input & Output Devices 4.2.4 Video <ul><li>To playback video on a standard computer it will need to be decompressed by hardware or software, usually on the card. </li></ul><ul><li>Standards </li></ul><ul><li>AVI – (Audio Video Interleave) or Video for Windows. Being replaced by Active Movie which will playback AVI, QuickTime and MPEG. </li></ul><ul><li>QuickTime – CODEC s/w developed by Apple but used by both Mac and PC. </li></ul><ul><li>MPEG – Video board uses hardware to make compression much faster. </li></ul><ul><li>Accuracy – Depends on Compression Technique, frame rate and resolution. </li></ul><ul><li>Speed – Hardware must be fast enough to cope with stream of data to memory and to the hard disk. </li></ul><ul><li>Cost – Not only card but good Multiscan Monitor required (17” and 19” nowadays) </li></ul>
64. 64. 4.2 – Input & Output Devices 4.2.5 Digital Camera <ul><li>Film replaced by an array of photosensitive cells. </li></ul><ul><ul><li>Images stored electronically using photosensitive diodes called charge coupled devices (CCDs) </li></ul></ul><ul><ul><li>Intensity of light recorded in an image. </li></ul></ul><ul><ul><li>Analogue values converted to digital using ADC </li></ul></ul><ul><li>Compression usually takes place. </li></ul><ul><ul><li>Bit map files turned into JPEG </li></ul></ul><ul><li>Image transferred to computer </li></ul><ul><ul><li>Serial Cable </li></ul></ul><ul><ul><li>“ Floppy Disk” adapter </li></ul></ul><ul><ul><li>Can then be printed, e:mailed etc. </li></ul></ul>
65. 65. 4.2 – Input & Output Devices 4.2.5 Digital Camera <ul><li>Accuracy </li></ul><ul><ul><li>Resolution </li></ul></ul><ul><ul><li>Measured in pixels or mega pixels – the more the better. E.g. 640 x 480 pixels or in megapixel mode 1280 x 960. </li></ul></ul><ul><ul><li>Accuracy depends on the array of photosensitive cells.. The more sensors and the smaller they are the higher the resolution. </li></ul></ul><ul><ul><li>Bit Depth </li></ul></ul><ul><ul><li>Number of bits in proportional to the number of colours that can be represented. </li></ul></ul><ul><li>Capacity </li></ul><ul><ul><li>Based on resolution and memory in the device. </li></ul></ul><ul><ul><li>Compression v altering resolution </li></ul></ul><ul><li>Cost </li></ul><ul><ul><li>Dropping as they become more common. </li></ul></ul><ul><ul><li>Resolution main factor and also facilities (zoom, flash etc.). </li></ul></ul>
66. 66. 4.2 – Input & Output Devices 4.2.6 Printers – Ink Jet Printer <ul><li>Ink-jet Printers are based on one of three different types of technology: continuous flow ink-jet, liquid ink-jet or phase-change ink-jet. We will look at how a liquid ink-jet printer works. </li></ul><ul><li>Liquid ink-jet or bubble-jet , operates by squirting tiny droplets of ink onto the page. The ink is first heated by passing an electric current through a coil. In milliseconds a bubble of vapour appears, forcing a tiny drop of ink from the nozzle onto the paper. </li></ul><ul><li>Resolution is typically 300 to 600 dots per inch, support the printing of text and graphics, colour and a range of shades. </li></ul><ul><li>Speed is pretty slow with a range of 4 pages per minute to 8 pages per minute, depending upon the model. </li></ul>
67. 67. 4.2 – Input & Output Devices 4.2.6 Printers – Laser Printer <ul><li>This type of printer uses lasers to &quot;write&quot; a page image onto a special drum as an electrostatic charge. The charged drum attracts toner particles which are transferred to the page and heated to set the image. </li></ul><ul><li>Usually a page is composed in the printer (often PostScript ). </li></ul><ul><li>Capacity </li></ul><ul><ul><li>On board RAM & processor needed to compose pages. The more RAM the higher quality graphics can be printed. </li></ul></ul><ul><li>Resolution </li></ul><ul><ul><li>600 dpi quite common (300 cheaper, 1200 expensive) </li></ul></ul><ul><li>Speed </li></ul><ul><ul><li>The faster in pages per minute (ppm) the dearer ranges from 4 ppm to 20 ppm with 12 ppm being about average. </li></ul></ul>
68. 68. 4.2 – Input & Output Devices 4.2.7 Multiscan Monitor The CRT is the basis of most visual display technology. The screen is arranged as a series of lines of dots and each dot is made up of three small areas of red, green and blue called a triad. The intensity of light shone on each triad determines the actual colour of the pixel. The picture is redrawn between 50 and 100 times a second. This is the refresh rate. A monitor which operate at different refresh rates is known as a multiscan or multisync monitor. The refresh rate is controlled by the video adapter. Screen resolution is quantified by the dot pitch, the distance between the dots on the screen. Typically between 0.28 and 0.38mm, corresponding to 100 to 70 dpi.
69. 69. 4.3 Selecting hardware to match operational requirements <ul><li>When given a scenario like setting up a library system you will have to consider:- </li></ul><ul><ul><li>RAM requirements </li></ul></ul><ul><ul><ul><li>Memory must be enough to run the software and support all the data in the system. </li></ul></ul></ul><ul><ul><li>Backing Storage </li></ul></ul><ul><ul><ul><li>Big enough to hold the O/S, Applications and data. </li></ul></ul></ul><ul><ul><li>Processor Performance </li></ul></ul><ul><ul><ul><li>Usually as fast as you can afford but must be fast enough to support all the applications recommended. </li></ul></ul></ul><ul><ul><li>Peripherals </li></ul></ul><ul><ul><ul><li>Specify type of printer, monitors etc. </li></ul></ul></ul><ul><ul><li>Communications </li></ul></ul><ul><ul><ul><li>Attached to a network or set up a new network. Internet connection (broadband?) </li></ul></ul></ul>
70. 70. 4.4 Buffers and Spoolers 4.4.1 Buffering <ul><li>Buffer </li></ul><ul><ul><ul><li>area of memory used to transfer data between the computer and a peripheral. </li></ul></ul></ul><ul><ul><ul><li>Used when a fast acting part of the system exchanges data with a slow peripheral </li></ul></ul></ul><ul><ul><ul><li>Buffer stores the data until peripheral can act on it. </li></ul></ul></ul><ul><ul><li>Peripheral Buffer </li></ul></ul><ul><ul><ul><li>E.g. printer – very slow. Has on board RAM to store the incoming data (laser may have 8MB) </li></ul></ul></ul><ul><ul><ul><li>E.g. Mass storage (disks). Data transferred in blocks so whole block transferred, managed by buffering </li></ul></ul></ul><ul><ul><li>Interface Buffer </li></ul></ul><ul><ul><ul><li>Universal Asynchronous Receiver/Transmitter (UART) handles transfer of serial to parallel and vice versa. </li></ul></ul></ul>
71. 71. 4.4 Buffers and Spoolers 4.4.2 Spooling When large amounts of data are to be sent to a peripheral device, or when the peripheral is shared across a network then spooling is a preferred method of compensating for the difference in speeds of the processor and the peripheral. Spooling involves the input or output of data to a tape or a disk. This, for example, allows output to be queued from many different programs and sent to a printer by a print spooler (special operating system software). The print spooler stores the data in files and sends it to the printer when it is ready, using a print queue .
72. 72. 4.5 – Storage Devices 4.5.1 Magnetic Magnetic storage devices include hard disks, floppy disks, Zip disks and magnetic tape. They are called magnetic storage devices because their recording surfaces are coated with a material that responds to magnetic fields to enable data to be stored. Storage devices can be fixed or removable. Removable storage devices allow the user to disconnect the device and physically transport data from one computer to another. Varieties of removable devices include the Iomega and Syquest hard disks and Jaz cartridges.
73. 73. 4.5 – Storage Devices 4.5.1.1 Magnetic Disk <ul><li>All the sectors around the disk, equidistant from the centre, form a track . With multiple platters, the collection of tracks on each platter, equidistant from the spindle is called a cylinder. When data is to be read or written, the read and write heads are moved to the appropriate track, where they wait until the relevant sector spins past. </li></ul><ul><li>Speed </li></ul><ul><li>Rotational speed of hard disks has improved, from 3000 (rpm) of early disks, to current rotational speeds of 5,400 and even 7,200 rpm. </li></ul><ul><li>Performance is also measured in terms of the rate of data transfer from the disk. </li></ul><ul><li>SCSI - transfer rate 5Mb/sec </li></ul><ul><li>Ultra Fast SCSIIII transfer rates - 40 Mb/sec . </li></ul>
74. 74. 4.5 – Storage Devices 4.5.1.1 Magnetic Disk <ul><li>Capacity </li></ul><ul><li>Hard disks have improved tremendously in their capacity to store data in the last 10 years. From the modest 10Mb disks of the early 80s to current 80 Gbyte disks on many of today’s PCs. </li></ul><ul><li>Access </li></ul><ul><li>The hard disk is a direct access device, meaning that data can be directly read or written to any portion of the disk. </li></ul>
75. 75. 4.5 – Storage Devices 4.5.1.2 Magnetic Tape Storing data on tapes used to be the only solution to backing up hard disks of large capacity. Now, with large, removable magnetic disks and optical CR-RW technology, this is no longer the case. However, removable storage media is comparatively expensive, costs 10 times tape. Tape, therefore, still has the edge in this market. Tape is read and written on a tape drive. Data is written to tape in blocks with inter-block gaps between them. A single operation writes each block Data is stored on magnetic tape as magnetised regions on the surface of the tape induced by the magnetic recording head. To read data, the tape passes under the read/write head and the stored magnetised regions produce very small voltages in the head, leading to a current in the head coil. This current can be analysed to give a representation of the stored binary data.
76. 76. 4.5 – Storage Devices 4.5.1.2 Magnetic Tape Capacity Magnetic tapes have large capacities, reaching up to several gigabytes and come in a variety of sizes and formats. Since their introduction, tape drives have passed through many stages of improvement with extremely reliable Digital Audio Tape (44.1 kHz, 16-bit record and playback DAT) drives representing the current state of the art. A 4mm DAT tape can now store up to 24 Gbytes of data! Access Tapes are sequential access devices. Accessing data on tapes is therefore much slower than accessing data on disks. They are not suitable as storage media for applications where data needs be used regularly - where a disk is a more appropriate medium. Because tapes are so slow, they are generally used only for long-term storage and backup.
77. 77. 4.5 – Storage Devices 4.5.2 Optical Storage <ul><li>CD-ROM </li></ul>A plastic disk is scanned using a laser. It reflects off pits on the surface differently from lands (bumps) Re-writeable CD-ROM becoming more common. Capacity – About 650Mb Speed – from single (150KB/sec) to 32x (or even 40x). The x refers to the times faster than CD Audio. Cost – CD-ROM Drives fairly cheap. Access – Always random
78. 78. 4.5 – Storage Devices 4.5.3Magneto Optical Storage <ul><li>Based on a combination of magnetic and optical technologies. </li></ul><ul><li>Active layer is magnetic material. </li></ul><ul><li>Recording – magnetic material heated beyond a particular temperature by laser, allows magnetisation to be reversed. </li></ul><ul><li>Reading – laser operates at much lower temp and reflected beam rotated by magnetic field and detected by read head. </li></ul><ul><li>Capacity – 3.5” disks of 128, 230 and 384 Mb </li></ul><ul><li>Speed – Varies as multiple of standard single speed </li></ul><ul><li>Cost – decreasing with time with different formats and capacities becoming available. </li></ul>
79. 79. 4.5 – Storage Devices 4.5.4 Solid State Storage Devices (SSSD) <ul><li>Solid-state storage devices are made up entirely from electronic components i.e. they have no moving parts. </li></ul><ul><li>They are also called RAM disks, as they take the place of a magnetic disk as a mass storage device. </li></ul><ul><li>They can be in the form of a plug-in card or cartridge containing memory chips. </li></ul><ul><li>The chips of a SSSD are typically static RAM or Electrically Erasable Programmable ROM (EEPROM or Flash EPROM). </li></ul><ul><li>SSSD are used with devices where space is at a premium e.g. in a camera, or when portability is desirable e.g a USB flash drive. </li></ul>
80. 80. 4.6 Interfacing (1) <ul><li>Interfacing means making the hardware connections so that two devices can communicate effectively. </li></ul><ul><li>Data Format – data has to be consistent e.g. serial output to a serial device. Interface makes data consistent (also ADC) </li></ul><ul><li>Parallel/Serial – time & space division. Time separates transmission of actual bits and space can be used for multiple bits in parallel. Serial can be slow but use of fibre-optic cable very fast. </li></ul><ul><li>Voltage – different voltage levels between peripheral & computer need to be ironed out. </li></ul><ul><li>Protocols – rules that govern transmission of data. E.g. no of bits per packet, voltage levels etc. </li></ul>
81. 81. 4.6 Interfacing (2) <ul><li>Status signals from a device indicate what the device is doing at any given moment. E.g.if a device is unable to receive data, then a transmitting device can delay transmission and retry later. </li></ul><ul><li>Speed - Different devices send and receive data at different rates. The devices agree a rate prior to transmission by utilising a protocol. </li></ul><ul><li>Wireless communications can be achieved using WAP (Wireless Application Protocol) - a specification for a set of communication rules to standardise the way that wireless devices, such as cellular telephones and radio transceivers, can be used for Internet access, including e-mail, the World Wide web , newsgroups , and Internet Relay Chat (IRC). Interconnecting devices centred around an individual person is called a wireless personal area network (WPAN). Typically, a WPAN uses technology that permits communication between devices in a </li></ul><ul><li>short radius of about 10 metres. One such technology is Bluetooth. </li></ul>
82. 82. 5 Networking 5.1 Introduction <ul><li>This unit on Networking considers the basic system topologies and functions that allow computers to operate on a network. </li></ul><ul><li>Various types of networks are considered ranging from small peer-to-peer networks to LANs, WANs and the Internet. </li></ul><ul><li>Comparisons are made between the various networks in terms of type and scale and the effects of network failures. </li></ul>
83. 83. 5 Networking 5. 2 Networks <ul><li>connecting t wo or more computers together turns them into a computer Network . </li></ul><ul><li>connecting two computer networks together creates an Internetwork . </li></ul><ul><li>connecting millions of computers and computer networks together forms a huge internetwork or what we now refer to as the Internet . </li></ul><ul><li>Economic and Social reasons for networks – desire to communicate probably most powerful reason. </li></ul><ul><li>We take e-mail, Internet, Video conferencing for granted but none of the were obvious when networks first appeared. </li></ul>
84. 84. 5 Networking 5. 2 Categorising Computer Networks <ul><li>Computer networks can be categorised by the rate at which data can be transferred between machines (Bandwidth), and the physical distance between them. </li></ul><ul><li>Greater distance suggests lower bandwidth. </li></ul><ul><li>Local Area Networks (LANs) – high bandwidth. </li></ul><ul><li>Wide Area Networks (WANs) – low bandwidth (even broadband is slow compared to typical modern LAN bandwidth) </li></ul>
85. 85. 5 Networking 5. 2.1 Local Area Networks (LANs) <ul><li>LANs very popular now and the technology has become much cheaper . </li></ul><ul><li>Sharing resources </li></ul><ul><ul><li>LAN belongs to single organisation on a single site so a high level of trust develops. </li></ul></ul><ul><ul><li>Share printers, scanners, hard disk space, applications and Internet connections </li></ul></ul><ul><li>Sharing Information </li></ul><ul><ul><li>Files and data. E-mail and appointments diaries, Intranet. </li></ul></ul><ul><li>Sharing Services </li></ul><ul><ul><li>Centralised backup, technical support, anti-virus, software installation and update. </li></ul></ul>
86. 86. 5 Networking 5. 2.1 (LANs) - Hardware <ul><li>Reduced Hardware costs have helped dramatic increase in LANs </li></ul><ul><ul><li>Network card – every PC on network needs a card to interface with the network. </li></ul></ul><ul><ul><li>Hubs – typically 24 ports, each PC connects to port. Can be slow and cause bottlenecks. </li></ul></ul><ul><ul><li>Switches – intelligent hubs (24 or racks of 24 x 8) – help reduce bottlenecks. </li></ul></ul><ul><ul><li>Software is now much cheaper. Each station needs a network licence and server software needs to be licensed for the number of stations on the network </li></ul></ul>
87. 87. 5 Networking 5. 2.1.1 Sharing Resources on a LAN <ul><li>Hardware resources </li></ul><ul><ul><li>Expensive printers (laser and colour laser), plotters and hard disks not only shared to save money but installation and maintenance cheaper and easier. </li></ul></ul><ul><li>Software Resources </li></ul><ul><ul><li>Can set up an Intranet, use internal e:mail and Newsgroups. </li></ul></ul><ul><ul><li>Also search facilities across the network. </li></ul></ul>
88. 88. 5 Networking 5. 2.1.2 Sharing Services on a LAN <ul><li>Network Manager </li></ul><ul><ul><li>Controls the network from any location </li></ul></ul><ul><ul><li>Controls software installation and upgrades centrally. </li></ul></ul><ul><ul><li>Control shared Internet access and Firewall protection. </li></ul></ul><ul><ul><li>Provide automatic virus protection </li></ul></ul><ul><ul><li>Do regular full backups and frequent (daily) incremental backups. </li></ul></ul>
89. 89. 5 Networking 5. 2.2 Wide Area Networks - WANs <ul><li>A WAN allows an organisation to maintain its management structure despite being geographically distributed around the world. </li></ul><ul><li>WAN’s & Internet increasingly popular as cost of communication drops. </li></ul><ul><li>Easier and cheaper to conduct business and communicate around the world. </li></ul>
90. 90. 5 Networking 5. 2.2.1 Metropolitan Area Networks - MANs <ul><li>A MAN is a wide area network which has a city or metropolitan area as its geographical limit. </li></ul><ul><ul><li>MANs are usually under the control of a single local authority </li></ul></ul><ul><ul><li>typically consist s of a WAN which is administered centrally, providing networked services to local government offices, schools, libraries, community centres etc. </li></ul></ul><ul><ul><li>advantages of a MAN are the economies of scale and the improved communications which can be achieved by connecting local government offices together. </li></ul></ul><ul><ul><li>Local authorities usual host an Intranet for use of a staff on-line newsletter </li></ul></ul><ul><ul><li>MANs rely on a high bandwidth and are really only suitable for Urban areas. Rural authorities have to use lower bandwidths (e.g. up to 2 Mbits/sec </li></ul></ul>
91. 91. 5 Networking 5. 2.2.2 Improved communications on a WAN <ul><li>E:mail allows users to communicate. </li></ul><ul><ul><li>Text and graphic messages </li></ul></ul><ul><ul><li>File transfer by attaching files to e:mails </li></ul></ul><ul><li>Newsgroups are electronic bulletin boards </li></ul><ul><ul><li>Organised by threads of messages </li></ul></ul><ul><ul><li>Can be set up and accessed if you have access to a News Server </li></ul></ul><ul><li>Electronic Forums </li></ul><ul><ul><li>Similar to newsgroups but controlled by a particular organisation e.g. on the BBC website forums exist for news, sport etc. </li></ul></ul><ul><li>List Servers </li></ul><ul><ul><li>Use e:mail to distribute messages rather than the user having to log onto a forum. </li></ul></ul>
92. 92. 5 Networking 5. 2.2.2 Improved communications on a WAN -2 <ul><li>File Transfer Facilities </li></ul><ul><ul><li>Being able to transfer files over a WAN means that if the product you sell can be stored or transmitted electronically, then you can sell it to anyone who is connected to the Internet without having to transfer a physical object. </li></ul></ul><ul><ul><li>Items on sale over the Internet which can be electronically distributed are things like software, music, photographic images, video and information in the form of data files. </li></ul></ul><ul><ul><li>Some companies are now offering services such as remote backup and data storage over the Internet. </li></ul></ul><ul><li>Distributed Processing </li></ul><ul><ul><li>Different parts of a suite of programs can be run on different machine across the network. </li></ul></ul><ul><ul><li>Allows software vendors to rent software rather than sell it. </li></ul></ul><ul><ul><li>Search for Extraterrestrial Intelligence (SETI) uses volunteers whose computers process distributed data when idle. </li></ul></ul>
93. 93. 5 Networking 5. 2.2.3 Access to information on a WAN <ul><li>Information Services </li></ul><ul><ul><li>Internet access means you have instant access any time of the day or night without having to travel, to news, technical information and other data. </li></ul></ul><ul><ul><li>Use a search engine on the web e.g. google </li></ul></ul><ul><li>Entertainment Services </li></ul><ul><ul><li>Internet radio, music channels and network games all possible on a low bandwidth. Information is broadcast once rather than being requested and transmitted separately for each user. </li></ul></ul><ul><ul><li>Video on demand needs a high bandwidth and other services benefit from high bandwidth. </li></ul></ul>
94. 94. 5 Networking 5. 2.2.4 Teleworking <ul><li>Tele- working </li></ul><ul><ul><li>mean s working from home instead of traveling to an office every day </li></ul></ul><ul><ul><li>Us e communications technology to keep in touch with your employer. </li></ul></ul><ul><ul><li>Can work in different country. </li></ul></ul><ul><ul><li>Any job where where the results of your labour can be transmitted electronically can be classed as teleworking. </li></ul></ul><ul><li>Video conferencing </li></ul><ul><ul><li>Allows people to see and hear the people they are having a meeting with. </li></ul></ul><ul><ul><li>Need specialised equipment and a high bandwidth. </li></ul></ul>
95. 95. 5 Networking 5. 2.2.4 Teleworking – advantages and disadvantages <ul><li>Advantages </li></ul><ul><ul><li>Employee saves time and money travelling, on childcare and can live in cheaper housing away from city. Deliver your work electronically. </li></ul></ul><ul><ul><li>Employer saves money on office space; tele-workers usually work harder – no distractions. Save wages by employing people in countries where wages are low. </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>Employee feelings of isolation, office chat and miss out on promotion. May work much harder and put in more hours than being paid. </li></ul></ul><ul><ul><li>Employer needs to pay for training and installation of communications equipment. Security issues if employees log into the company network from home </li></ul></ul>
96. 96. 5 Networking 5. 2.3 Intranets <ul><li>Intranets </li></ul><ul><ul><li>Used by organisations to distribute information on a LAN </li></ul></ul><ul><ul><li>Often used as a portal for the Internet and difficult to tell whether you are on the LAN or WAN </li></ul></ul><ul><ul><li>Usually private and internal </li></ul></ul><ul><ul><li>Can be used by companies with branches all over the world as secure information service. </li></ul></ul>
97. 97. 5 Networking 5. 2.4 Mainframe Networks <ul><li>Mainframe network with “Dumb” terminals </li></ul><ul><ul><li>Original communication method everyone used the same computer. </li></ul></ul><ul><ul><li>Terminal has no processing power. </li></ul></ul><ul><ul><li>Mainframe processor, memory and disks used by each terminal in turn. </li></ul></ul><ul><ul><li>Current mainframes combined with conventional client-server networks. Client access mainframe via terminal emulation software </li></ul></ul><ul><li>Thin client Networks </li></ul><ul><ul><li>Low power workstations run applications on the server. </li></ul></ul><ul><ul><li>Load O/S and software from the server. </li></ul></ul><ul><ul><li>Server must be very powerful high spec with lots of memory. </li></ul></ul><ul><ul><li>Useful for single application stations e.g. Internet Browser only. </li></ul></ul>
98. 98. 5 Networking 5. 3 Network Operating Systems <ul><li>Improved networking operating systems </li></ul><ul><ul><li>Easier to connect computers together </li></ul></ul><ul><ul><li>Modern O/S has networking built-in </li></ul></ul><ul><ul><li>Common standards such as TCP/IP </li></ul></ul><ul><ul><li>has made networking easier and cheaper. </li></ul></ul><ul><li>Main Functions of Network O/S </li></ul><ul><ul><li>Allows users to treat resources on other computers as if they were local resources </li></ul></ul><ul><ul><ul><li>Mapping directories or drives of remote machines </li></ul></ul></ul><ul><ul><ul><li>Copying remote files to local drives </li></ul></ul></ul><ul><ul><ul><li>Managing different operating systems on the network </li></ul></ul></ul><ul><ul><ul><li>Ensuring data integrity </li></ul></ul></ul><ul><ul><ul><li>Providing privacy and security of network resources </li></ul></ul></ul>
99. 99. 5 Networking 5. 3.1 Client-Server Network <ul><li>Central server or servers </li></ul><ul><ul><li>Usually most powerful computers on the network. </li></ul></ul><ul><ul><li>RAID drives and lots of memory </li></ul></ul><ul><ul><li>Often run a different O/S to clients </li></ul></ul><ul><ul><li>Provide access to shared resources without affecting the performance of any one machine. </li></ul></ul><ul><ul><li>May act as mail servers, Intranet or proxy servers, networked storage or applications servers or news servers. </li></ul></ul>
100. 100. 5 Networking 5. 3.1 Client-Server Network Services <ul><li>Security </li></ul><ul><ul><li>Network software allows only users with correct passwords to access the system and files they have permission to use. </li></ul></ul><ul><li>Networked storage </li></ul><ul><ul><li>You can access centrally stored files from any machine on the network. </li></ul></ul><ul><li>Communications </li></ul><ul><ul><li>Internal & external e:mail, Intranet services. </li></ul></ul><ul><ul><li>Internet and Firewall services </li></ul></ul><ul><li>Applications </li></ul><ul><ul><li>Applications stored centrally mean you always have access to that application even if it is not installed on your workstation. </li></ul></ul><ul><li>Support Services </li></ul><ul><ul><li>Virus checking, remote control, remote monitoring and central backup strategy. </li></ul></ul>
101. 101. 5 Networking 5. 3.1.1 Advantages of Client-Server Network <ul><li>Centralised control </li></ul><ul><ul><li>Of software installation </li></ul></ul><ul><ul><li>Over software versions </li></ul></ul><ul><ul><li>Ability to configure stations to a common format. </li></ul></ul><ul><li>Resources shared </li></ul><ul><ul><li>Hard disk space, expensive peripherals (laser & colour laser printers), modems and routers. </li></ul></ul><ul><li>Security </li></ul><ul><ul><li>Access to file and other resources easily implemented. </li></ul></ul><ul><li>Backup routines </li></ul><ul><ul><li>Easy to backup central server to tape either full or incremental backup </li></ul></ul><ul><li>Ease of expansion </li></ul><ul><ul><li>Most LANs can easily be extended by adding cables and stations. </li></ul></ul>
102. 102. 5 Networking 5. 3.1.1 Disadvantages of Client-Server Network <ul><li>Cable Faults </li></ul><ul><ul><li>In a bus topology can bring down whole sections of the network </li></ul></ul><ul><li>Server Failure </li></ul><ul><ul><li>Will bring down the entire network. </li></ul></ul><ul><li>Software incompatibility </li></ul><ul><ul><li>Some network s/w is proprietary and difficult to link to other LANs </li></ul></ul><ul><li>Management & Control </li></ul><ul><ul><li>The bigger the network the more highly trained and expensive the technician or controller is to employ. </li></ul></ul>
103. 103. 5 Networking 5. 3.2 Peer to Peer Networks <ul><li>Peer to peer </li></ul><ul><ul><li>All machines on network of equal status. </li></ul></ul><ul><ul><li>No server on network </li></ul></ul><ul><ul><li>Suitable for small (up to 5 stations) LANs. </li></ul></ul><ul><ul><li>Used in home situations </li></ul></ul><ul><ul><li>Also in small offices where all staff are trusted </li></ul></ul><ul><ul><li>Security difficult to implement </li></ul></ul><ul><ul><li>Bottlenecks can occur if more than one user wishes to access the same resource (e.g. hard disk) at the same time. </li></ul></ul>
104. 104. 5 Networking 5. 3.2 Advantages of Peer to Peer Networks <ul><li>P eer to peer networks are cheap and easy to implement . </li></ul><ul><li>M odern operating systems like Windows 98 and Apple OSX have this sort of networking built in </li></ul><ul><li>you do not have the expense of providing a dedicated machine to function as a server </li></ul><ul><li>I f security is not a problem, then it is very convenient to be able to share files, access peripherals and have several people using the same Internet connection without having to set up a more complex network structure. </li></ul>
105. 105. 5 Networking 5. 3.2 Disadvantages of Peer to Peer Networks <ul><li>Organisation and management become difficult when several machine connected together and sharing files </li></ul><ul><li>Versions of installed software are difficult to control. </li></ul><ul><li>Backup difficult as files distributed across several machines. </li></ul><ul><li>Proper security difficult as no easy way to restrict access to shared files or resources. </li></ul>
106. 106. 5 Networking 5. 3.3 Stations and servers <ul><li>Network stations and servers are nodes on the network . </li></ul><ul><li>Servers </li></ul><ul><ul><li>A server usually refers to a program and the computer it is running on. </li></ul></ul><ul><ul><li>Servers provide access to resources on a network. </li></ul></ul><ul><ul><li>On a network, one machine may provide access to a number of different resources </li></ul></ul><ul><ul><li>T here may be a number of different machines acting as servers, each one providing access to different resources. </li></ul></ul><ul><li>Machine identification </li></ul><ul><ul><li>All nodes on a network, whether they are servers or network stations, will have a unique identity which identifies that particular machine. </li></ul></ul><ul><ul><li>The type of identity a node has will be determined by the protocols running on the network. </li></ul></ul>
107. 107. 5 Networking 5. 3.3 Stations and servers - 2 <ul><li>Machine identification – Ethernet Standard </li></ul><ul><ul><li>Every network interface card has a Media Access Control (MAC) address – 6 bytes </li></ul></ul><ul><ul><li>In TCP/IP every node has its own IP address – 4 bytes. </li></ul></ul><ul><ul><li>Nodes may also have a network name. </li></ul></ul>
108. 108. 5 Networking 5. 3.3 Stations and servers – Network Servers <ul><li>File Server </li></ul><ul><ul><li>Controls log-ins and gives users access to files </li></ul></ul><ul><li>Print Server </li></ul><ul><ul><li>Allows a user access to a shared printer. </li></ul></ul><ul><li>Applications Server </li></ul><ul><ul><li>Distributes applications around the network (read only access) to users. </li></ul></ul><ul><li>E:mail Server </li></ul><ul><ul><li>Stores users’ e:mails and account details. Regularly contacts external e:mail server to send and receive external mail. </li></ul></ul><ul><li>News Server </li></ul><ul><ul><li>Stores and forwards messages posted by users on a bulletin board system. </li></ul></ul><ul><li>Web Server </li></ul><ul><ul><li>Transmits and stores Web pages and provides access to to an Intranet. </li></ul></ul><ul><li>Proxy Server </li></ul><ul><ul><li>Connects a LAN to the Internet. Allows many users simultaneous access. </li></ul></ul>
109. 109. 5 Networking 5. 4 Network Topology <ul><li>A network topology describes the arrangement of computers to form a network. The actual physical layout is determined by the buildings or other locations that house the parts of the network. </li></ul><ul><li>We will look at four local area network topologies. </li></ul><ul><ul><li>Bus </li></ul></ul><ul><ul><li>Star </li></ul></ul><ul><ul><li>Ring </li></ul></ul><ul><ul><li>Mesh </li></ul></ul>
110. 110. 5 Networking 5.4.1 Network Topology - Bus 4 Factors Affecting Performance 4.6. Network Topology - Bus Bus Topology- easy to expand and cheap to set up. e.g. Ethernet in school or college. Data Security – data encryption methods used. High collision rates requiring re-transmission Bandwidth – available bandwidth shared amongst all stations accessing network. Data compression used. Reliability – fault in one station has no effect on rest. Cable fault will lose all that section. Cost – relatively cheap
111. 111. 5 Networking 5.4.2 Network Topology - Star Data Security – higher security as data routed only to the computer that is to receive it. No collisions. Reliability – if a link fails then only that station is off the network. Failure to central controller is fatal. Cost – can be quite expensive due to high cost of cabling. Popular in small self-contained networks as not too expensive (small office). All nodes connected to one central node that routes traffic to the appropriate place.
112. 112. 5 Networking 5.4.3 Network Topology - Ring Ring Topology Similar to Bus in many respects with similar security problems. Control system in charge of transmissions and stations guaranteed access to transmissions. Collisions avoided by use of a token Additional expense for control s/w and system. May have to wait turn to transmit. Network down to add station, but few if any crashes.
113. 113. 5 Networking 5.4.4 Network Topology - Mesh Mesh Topology Fault in one cable does not affect network. Multiple transmissions Lots of wiring Expensive Excellent performance
114. 114. 6 Using Networks 6.1 Introduction <ul><li>This unit considers :- </li></ul><ul><li>T he hardware and software required to use networks </li></ul><ul><li>The associated communications issues. </li></ul><ul><li>The misuse of networks is also considered and the implications discussed . </li></ul>
115. 115. 6 Using Networks 6.2.1 Network Hardware – The Hub <ul><li>A hub in an Ethernet network is a multi-port repeater. </li></ul><ul><li>Hubs are most often used on networks using UTP cabling as the limit for this type of cable is 100 metres. </li></ul><ul><li>A hub will divide the network up into a series of different segments, reducing the likelihood that a cable fault will bring the whole network down. </li></ul><ul><li>Hubs are commonly supplied with 12 or 24 ports, and are suitable for distributing a UTP cable to a room or office full of network stations. </li></ul><ul><li>A hub also functions at the lowest level of the OSI networking model, the Physical Layer . </li></ul>
116. 116. 6 Using Networks 6.2.2 Network Hardware – The Switch <ul><li>A switch (sometimes called a switched hub) divides the network up into collision domains. A Switch is often regarded as an intelligent Hub </li></ul><ul><li>A Collision occurs when a station begins transmission and then receives the beginning of a frame from another station. </li></ul><ul><li>T he station will immediately stop transmission and issue a JAM signal onto the segment. </li></ul><ul><li>This will indicate to the other transmitting station that a collision has occurred and both stations will back off for a random amount of time and try to re-transmit. </li></ul><ul><li>This back-off time is dependent on the number of consecutive collisions that were issued before a successful transmission. </li></ul><ul><li>The more collisions, the longer the maximum back-off time. </li></ul><ul><li>This mechanism requires that stations be close enough together for each station to see any possible attempted transmission before the first 64 bytes of its frame have been transmitted. </li></ul><ul><li>This is because 64 bytes is the minimum frame size for an Ethernet network. </li></ul>
117. 117. 6 Using Networks 6.2.3 Network Hardware – The Router <ul><li>A router works like a bridge on inter-networks using IP addresses. </li></ul><ul><li>Routers are used to link Ethernet networks to the Internet via fibre or ISDN and ADSL lines. </li></ul><ul><li>Routers can be programmed remotely to restrict access to certain IP addresses. </li></ul><ul><li>Possible to connect over 200 stations to the Internet and share the bandwidth intelligently. </li></ul>
118. 118. 6 Using Networks 6.2.4 Network Hardware – Network Interface Card <ul><li>Network Interface Card (NIC) </li></ul><ul><ul><li>Circuit board installed inside a computer to connect it to the network. </li></ul></ul><ul><ul><li>NIC must be designed for the network it is connected to e.g. Ethernet card for Ethernet LAN. </li></ul></ul><ul><ul><li>Provides a dedicated full time connection to the network. </li></ul></ul>
119. 119. 6 Using Networks 6.3 Hardware & Software Factors <ul><li>6.3.1 Processors </li></ul><ul><ul><li>Processor hungry applications run on networks (Browser, P2P. Virtual Private Networks) </li></ul></ul><ul><ul><li>Features to consider </li></ul></ul><ul><ul><ul><li>Performance (High Speed and throughput) </li></ul></ul></ul><ul><ul><ul><li>Flexibility (Ability to adapt to changing O/S and Application S/W) </li></ul></ul></ul><ul><ul><ul><li>Power (High power leads to heat – need cooling etc.) </li></ul></ul></ul><ul><ul><ul><li>Software Support (compilers, operating systems and libraries available to the processor) </li></ul></ul></ul>
120. 120. 6 Using Networks 6.3 Hardware & Software Factors <ul><li>6.3.2 Memory </li></ul><ul><ul><li>Factors defining the memory that supports a network processor can be categorised as follows: </li></ul></ul><ul><ul><ul><li>Shared, distributed or a combination </li></ul></ul></ul><ul><ul><ul><li>Size and type of memory used </li></ul></ul></ul><ul><ul><ul><li>Caches that are included on or off the chip </li></ul></ul></ul><ul><ul><li>Memory is available as RAM, on the NIC and shared from a server. Also can use a NMS (Network Memory server) – provides RAM as fast network memory paging. </li></ul></ul><ul><ul><li>Special Features </li></ul></ul><ul><ul><ul><li>Memory / buffer controllers </li></ul></ul></ul><ul><ul><ul><li>Packet management units </li></ul></ul></ul><ul><ul><ul><li>Address generation units </li></ul></ul></ul>
121. 121. 6 Using Networks 6.3 Hardware & Software Factors <ul><li>6.3.3 Backing Storage </li></ul><ul><ul><li>Local storage on PC and remote network storage. </li></ul></ul><ul><ul><li>Hard disks used throughout </li></ul></ul><ul><ul><li>Specialised RAID systems used on shared network disks </li></ul></ul><ul><ul><li>Some systems separate from main server and accessed via a storage server. </li></ul></ul><ul><ul><li>Shared drives are assigned a network address allowing them to be accessed. E.g. Each “Home” drive has an address tied in with its owner’s account. </li></ul></ul>
122. 122. 6 Using Networks 6.3 Hardware & Software Factors <ul><li>6.3.4 Browsers </li></ul><ul><ul><li>A browser is the application program that enables a computer user, to look at, and interact with World Wide web. </li></ul></ul><ul><ul><li>It makes requests to web servers throughout the Internet. </li></ul></ul><ul><ul><li>Netscape Navigator and Microsoft Internet Explorer are the only two browsers that the vast majority of Internet users are likely to use. </li></ul></ul><ul><ul><li>The notion of a browserless web describes communication over the World Wide web between programs rather than between people using browsers and web servers and does not involve an interactive user. </li></ul></ul>
123. 123. 6 Using Networks 6.3 Hardware & Software Factors <ul><li>6.3.5 Network Operating Systems </li></ul><ul><ul><li>Server runs a specialised NOS </li></ul></ul><ul><ul><ul><li>Windows NT, Server 2000, Server 2003 </li></ul></ul></ul><ul><ul><ul><li>Unix based variations including Linux (open source). </li></ul></ul></ul><ul><ul><li>Workstations run client based O/S </li></ul></ul><ul><ul><ul><li>NT for Workstations, Widows 98, 2000, XP </li></ul></ul></ul><ul><ul><ul><li>Server can cope with mixture of client O/S on the network (inc Mac OS) </li></ul></ul></ul><ul><ul><li>Transparency needed e.g. </li></ul></ul><ul><ul><ul><li>Printing or Saving a file should be the same operation whether locally or on the network. </li></ul></ul></ul><ul><ul><ul><li>Achieved using a network driver called a Redirector </li></ul></ul></ul>
124. 124. 6 Using Networks 6.4 Technical Factors Affecting Communications The technical factors which have led to the growth of computer networks have emerged in parallel with t he economic factors which have driven the research into networking technology. As the economic demand or networking technology has grown, the trend has been for equipment prices to fall and performance to increase. Although still in its infancy, the development of wireless networking is likely to follow the same pattern.
125. 125. 6 Using Networks 6.4.1 Cabling <ul><li>Cabling can affect bandwidth and different cabling is used in different situations. </li></ul><ul><ul><li>As more networks are installed the cost of cabling has fallen. </li></ul></ul><ul><ul><li>Different cables used in different situations (even on one network) </li></ul></ul><ul><ul><ul><li>Ethernet uses UTP cabling (developed by Xerox) running at 100Mb/sec. </li></ul></ul></ul><ul><ul><ul><li>Fibre Optic cable used to join areas of the network to the server. Very fast (e.g. 2Gb/sec) allowing many stations to share the bandwidth. Connects Hubs/Switches to a server. </li></ul></ul></ul>
126. 126. 6 Using Networks 6.4.2 Bandwidth <ul><li>The term bandwidth describes the rate at which data can be transmitted over a segment of a network. </li></ul><ul><li>As users share networks the Bandwidth available to each user depends on the number of users. To maximise bandwidth either increase overall or reduce the demand. </li></ul><ul><ul><li>Reducing the demand </li></ul></ul><ul><ul><ul><li>Data Compression – remove redundant information </li></ul></ul></ul><ul><ul><ul><li>Caching – Commonly viewed or used data stored locally to avoid transmission e.g. Internet home page. Most of a network profile. </li></ul></ul></ul><ul><ul><ul><li>Broadcasting - - if data such as video or audio is transmitted live, then although the user only has one chance of viewing it, the bandwidth requirements will be a lot less than if users are continually downloading their own copy of the data. </li></ul></ul></ul><ul><ul><li>Increasing capacity </li></ul></ul><ul><ul><ul><li>Fibre Optic and satellite links on a LAN, ISDN and ADSL on the Web. </li></ul></ul></ul>
127. 127. 6 Using Networks 6.4.3 Wireless <ul><li>Features </li></ul><ul><ul><li>Slower than conventional cabling. </li></ul></ul><ul><ul><li>Convenience of being able to move around rooms and buildings. </li></ul></ul><ul><ul><li>Quick and easy to install </li></ul></ul><ul><ul><li>Bluetooth allows devices such as mobile phones, printers and laptops to form a mini network when they are in close proximity. </li></ul></ul><ul><ul><li>Mobile phones can access the Internet via Wireless Application Protocol (WAP) </li></ul></ul>
128. 128. 6 Using Networks 6.5.1 Misuse of Networks – Social Issues <ul><ul><li>Personal privacy </li></ul></ul><ul><ul><ul><li>The monitoring of individuals’ Internet and email use is a contentious issue. Many governments would like to have access to this sort of information. Many individuals would not like them to have this kind of access. With modern communications networks it is theoretically possible to trace the movements of any individual around the world - they use cash machines, pay with credit cards, use the Internet, use mobile phones, appear on surveillance cameras, and may use electronic road tolling systems. All of these systems could be combined to track an individual’s movements. </li></ul></ul></ul><ul><ul><ul><li>Even organisations who manage LANs are becoming concerned about the security and employment issues surrounding email, and are starting to monitor all email activity on their networks to make sure that their employees are not divulging company secrets or using the network facilities for their own personal use. </li></ul></ul></ul>
129. 129. 6 Using Networks 6.5.1 Misuse of Networks – Social Issues <ul><li>Encryption </li></ul><ul><ul><li>Encrypting data is a method of coding it, in order to make it difficult or even impossible for someone to read it unless they have authorisation from you. Some governments make encrypting data illegal, others regard it as an individual right. T here is a trade-off between security and convenience. </li></ul></ul><ul><ul><li>Encryption is classified according to the number of bits needed for the key used to encode the data. The more bits that are used, the longer it takes for the code to be cracked. As computers increase in power, the time and resources needed to crack such codes decreases, so the minimum encryption key size needs to increase as computer technology improves. </li></ul></ul><ul><ul><li>At the moment email on most networks is un-encrypted and insecure, as messages are sent as plain ASCII text. One popular and free encryption system currently available is Pretty Good Privacy (PGP), although until recently PGP was regarded as “ mutinous “ by the USA government and its inventor was prosecuted for allowing details of how his system worked to be posted on the Internet. </li></ul></ul>
130. 130. 6 Using Networks 6.5.1 Misuse of Networks –Disconnection <ul><li>Disconnection </li></ul><ul><ul><li>Many people feel that the Internet has accentuated the difference between the rich and the poor. People in western countries are described as &quot;Information rich&quot; whereas most people in the Third World are &quot;Information poor&quot;, since connecting to to the Internet requires expensive equipment and access to a networking infrastructure which does not exist in many poor countries. </li></ul></ul>
131. 131. 6 Using Networks 6.5.1 Misuse of Networks – Social Isolation <ul><ul><li>Social isolation </li></ul></ul><ul><ul><ul><li>There is a fear that the increased use of electronic communication will mean that many people will become physically more isolated from each other. The Internet encourages the creation of global communities, but may result in neighbours not seeing each other for weeks on end. </li></ul></ul></ul>
132. 132. 6 Using Networks 6.5.2 Misuse of Networks – Ethical Issues <ul><li>Netiquette </li></ul><ul><ul><li>There are several conventions and a whole new vocabulary which has developed with regard to how you should behave on Internet newsgroups, using email, etc. Simple rules such as not sending &quot; spam &quot; (unsolicited commercial email), not shouting (writing in capital letters) and respecting people’s privacy may seem obvious, but it is easy to make mistakes without realising it. The best policy when subscribing to a newsgroup or joining a list server is to &quot;listen&quot; quietly for a while to see how others behave before you submit any contributions yourself. </li></ul></ul>
133. 133. 6 Using Networks 6.5.2 Misuse of Networks – Ethical Issues <ul><li>Misrepresentation </li></ul><ul><ul><li>The ability to post messages on newsgroups or discussion lists anonymously means that offensive statements can be made without the person making them being held to account. </li></ul></ul>
134. 134. 6 Using Networks 6.5.2 Misuse of Networks – Ethical Issues <ul><li>Surveillance and monitoring </li></ul><ul><ul><li>The email you send and receive, the pages you view and the files you download via the Internet can all be logged by a number of organisations. These organisations may not always have your best interests at heart. </li></ul></ul>
135. 135. 6 Using Networks 6.5.2 Misuse of Networks – Ethical Issues <ul><li>Chatrooms </li></ul><ul><ul><li>A re popular with young people who use the Internet as they enable users to communicate in real time with others from all over the world. A chatroom on the Internet is an area where users can type messages which can be read immediately by anyone else connected to the same server. Communication is slow because of the need to type the messages, but this disadvantage is outweighed by the immediacy of the system. One problem with chatrooms is that there is no way of verifying that the person you are communicating with is who they say they are. They may have lied about their age, their sex, or why they are interested in chatting with you. </li></ul></ul>
136. 136. 6 Using Networks 6.5.3 Misuse of Networks – Network Etiquette <ul><li>Netiquette </li></ul><ul><ul><li>While there are no international standards of behaviour on networks, there is an accepted code of conduct often referred to as netiquette. </li></ul></ul><ul><ul><li>Netiquette is usually just common sense. Network administrators are the only users of a network who have access to all the files on a network - it is considered unprofessional for a network administrator to access any personal file unless they are required to do so to perform their job. </li></ul></ul>
138. 138. 6 Using Networks 6.5.3 Misuse of Networks – Network Etiquette 2 <ul><li>Some network rules of etiquette on a WAN are: </li></ul><ul><ul><li>Avoid wasting bandwidth by sending unnecessary emails, attaching uncompressed files or creating web pages with large or unnecessary graphics on them; </li></ul></ul><ul><ul><li>Be aware that the Internet is used by people with a large variety of different machines running different operating systems and different browsers. If you want other users to access information, try to store the files in a format which is going to be easy to read for everyone. ASCII code is the simplest format for text. CSV is the simplest format for a database; </li></ul></ul><ul><ul><li>Try to create web pages which are readable no matter what resolution your monitor is set to use. </li></ul></ul>
139. 139. 6 Using Networks 6.5.3 Misuse of Networks – Network Etiquette <ul><li>Email etiquette </li></ul><ul><ul><li>email messages should be concise and to the point; </li></ul></ul><ul><ul><li>remember to make the subject line relevant to the message you are sending. </li></ul></ul><ul><ul><li>do not repeat email messages. Give the recipient time to read your email and to respond to it; </li></ul></ul><ul><ul><li>be professional and careful what you say about others. </li></ul></ul><ul><ul><li>email is not a secure means of communication as it is transmitted without encryption. </li></ul></ul><ul><ul><li>when being humorous, use emoti c ons to express humor. (Tilt your head to the left to see the emoti c on smile) :-) means happy face; </li></ul></ul><ul><ul><li>typing mail messages all in upper case is considered SHOUTING! and rude; </li></ul></ul><ul><ul><li>do not send people chain letters or hoax virus warnings. Such email just reduces the bandwidth available for everyone; </li></ul></ul><ul><ul><li>avoid sending anyone spam ; </li></ul></ul><ul><ul><li>do not attach large files to an email message without asking the recipient’s permission first. </li></ul></ul>
140. 140. 6 Using Networks 6.5.3 Misuse of Networks – Network Etiquette <ul><li>Usenet etiquette </li></ul><ul><ul><li>All of the email etiquette rules apply to Usenet. </li></ul></ul><ul><ul><li>remember to be courteous and respect others: </li></ul></ul><ul><ul><li>when quoting someone else, remove what is not directly applicable to your reply. </li></ul></ul><ul><ul><li>Do not automatically quote the entire body of messages you are replying to when it is not necessary. Leave only the minimum necessary to provide context for your reply. </li></ul></ul><ul><ul><li>it is extremely rude to forward personal email to mailing lists or a newsgroup without the original author’s permission. only messages meant to be read by the entire group should go to the list. Send a personal mail message aimed at one person to that person. </li></ul></ul><ul><ul><li>posting an advertisement in news groups, unless it is specially chartered for that purpose like the for-sale newsgroup, or sending unsolicited advertisements with email is considered rude. </li></ul></ul>
141. 141. 6 Using Networks 6.5.3 Misuse of Networks – Network Etiquette <ul><li>Listserver etiquette </li></ul><ul><ul><li>All of the Usenet etiquette rules apply to listservers, though as your messages will arrive as emails to the members of the list, it is best to be even more careful than when posting to a newsgroup. Some list servers generate large amounts of email every day. It is often wiser to receive the messages in digest form as one single email containing all the messages posted that day. </li></ul></ul><ul><ul><li>Here are a few guidelines: </li></ul></ul><ul><ul><ul><li>when signing up for a group, save your subscription confirmation email for reference, so that if you go on holiday or no longer wish to receive the list messages, you will have the subscription address for suspending mail; </li></ul></ul></ul><ul><ul><ul><li>if you lose interest in a list-server, un-subscribe from it so that the messages being sent to you do not clog up the network. </li></ul></ul></ul>
142. 142. 6 Using Networks 6.5.3 Misuse of Networks – Network Etiquette
143. 143. 6 Using Networks 6.5.4 Hacking <ul><li>Controlling access to the network </li></ul><ul><ul><li>The network operating system is responsible for security on the network. The most obvious example of this is when a user logs on. The user must supply an identity and a password. The operating system compares the data entered with the identities and passwords in its database and if the two do not match up then it will not allow that user any access to the resources on the network. </li></ul></ul><ul><ul><li>If the identity and password do match, then the resources which the user has access to will depend on the level of access that user has been given by the network manager. </li></ul></ul><ul><ul><li>The access a user has to resources depends on that user’s level of permissions . </li></ul></ul>