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1. COMPUTER
SYSTEM
UNIT TWO
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2. Computer system
 It is a system which has its own goal and different interrelated
component that work together for the achievement of common
goals.
It has two main categories
1.Hardware
2.Software
2

3. computer hardware
 Is the physical parts of the computer; the parts that you can see
and touch.
 It can broadly be divided into:
 Input Devices
 CPU/processer
 Memory / Storage Devices
 Output Devices
3

4. Input devices
 It lets us communicate with a computer.
 They are devices used to supply input (data/ instruction) to the
processing unit.
 There are different types of input devices.
 They differ in
 size
 data input method
 format of data entry, etc.
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5. some of the major input devices are:
 Pointing Devices ,
 A keyboard,
 scanner,
 digital camera,
 Microphone and
 Video Capture Card .
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6. Pointing Devices
 It move some object on the screen and can do some action
 Common pointing devices
 Mouse - most common pointing device
 Trackball has the ball on top and you move it with your finger.
 Touchpad allows you to move your finger across a pressure
sensitive pad and press to click.
 Joystick - consists of a handheld stick
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7. Keyboard
 Used to type data into the computer
 The standard keyboard contains 83 keys.
 Recent machines used enhanced keyboard that has up to 105 key.
 On modern key boards there are four major groups of keys
 Function keys usually labeled F1-F12 are used as command buttons for
applications. E.g. F1=HELP F5=REFREASH
 The type writer or alpha numeric keys are the alphabets a to z and the
numbers 0 to 9.
 Numeric key contains numbers, arithmetic operations and cursor movement
keys.
 Special keys include delete, shift, enter, end, control, alt, etc.
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8. Scanner
 It allows us to scan documents, pictures, or graphics and view
them on the computer.
 You can also use software to edit the items you scan.
 Used to put printed pictures and text into a computer
 Converts an image into dots that the computer can understand
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9. Digital Camera
 Used to take electronic pictures of an object
 The pictures taken by a digital camera can be used directly by a
computer
Microphone
 Used to put sound into a computer
 Need sound recording software
 Convert speech (analog s.) to digital form
Video Capture Card
 Use to put video into a computer
 Need a video source, either a video camera or video recorder
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10. The Processor/CPU
 It is a place where every activity of computer system is hold.
 Is considered as brain of computer.
 All the other components RAM, disk drives, the monitor exist
only to bridge the gap between you and the processor.
 Special processors such as that inside the key board also exist to
handle the signal generated whenever you press a key and
releases key.
 The current standard is an Intel Pentium micro processor chip.
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11. The CPU has three components
 The arithmetic logic unit (ALU)
 The control unit (CU)
 The registers
 ALU:
 is the place where the actual execution of the instructions takes place during
data processing operation.
 Is a place where the arithmetic operation and logical operation takes place.
 That is, when the control unit encounters an instruction that involves an
arithmetic operation (such as add, subtract, multiply divide) or a logical
operation (such as less than, equal to, greater than), it passes control to the
CPU.
11

12. Cont.…
 CU:
selects and interprets program instructions and then sees that
they are executed.
It doesn’t perform any actual processing on the data,
It manages and coordinates the entire computer system
including the input and out put units.
It obtains instructions from the program stored in the main
memory, interrupts the instruction, and issues signals that cause
other units of the system to execute.
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13. Cont.…..
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Registers:
 registers are temporary, high speed storage elements inside CPU.
 The length of a register equals the number of bits that it can
store. Thus a register that can store 8 bits is normally refereed to
as an 8 bit register.
 Most CPUs sold today have 32 bit or 64 bit register.

14. Memory
 The system memory is the place where the computer holds programs
and data that are in use.
 The capacity of a storage device is mostly measured in bytes. Other
measurements include:
 Kilo byte (KB) =210 bytes which is equal to 1024 characters.
 Megabyte (MB) = 220 bytes
 Gigabyte (GB)=230 bytes
 The two most important types of memory are:
 Primary memory
 Secondary memory
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15. Primary storage
 Presently known as memory.
 It is the only one directly accessible to the CPU.
 It is directly or indirectly connected to the CPU via BUS.
 It is much faster to access than secondary storage because of the
proximity of the storage to the processor.
 It can be divided into two essential types:
RAM
ROM
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16. Random access memory (RAM)
 It is temporary and volatile.
 It is a computer workspace where data and instruction for
immediate processing are held.
 It is the working area of the computer.
 It is dependent on the power supply.
 When first switched on RAM is empty until a program is loaded
into it.
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17. Read-only-memory (ROM)
 It is permanent
 Booting starts on ROM because it holds special program or
instructions
 POST (Power on Self Test) to make sure all its components are
working properly and to warn you if something is missed.
 It can’t be changed by the computer user.
 If ROM is damaged, the computer system simply can’t function.
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18. Secondary Storage device
 It is also called secondary memory or storage.
 It is not directly accessible by the CPU.
 It can save data, information, and programs for long periods of
time.
 It also can keep them even when the computer is turned off or
unplugged.
 The main types of secondary memory are categorized in to
 magnetic storage devices.
 optical storage devices
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19. Magnetic storage
 Use the principle of magnetism.
 It is non-volatile.
 Magnetic storage will take these forms:
 Magnetic disk
 Floppy disk
 Hard disk
 Magnetic tape used for back up purpose
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20. Optical Devices:
 It uses the principle of laser technology to store data on a hard plastic disk.
 It has three types
 read only storage :
 CD, CD-ROMS, and DVD
 write once :
 CD-R, DVD-R, DVD+R
 Rewrite storage:
 CD-RW, DVD-RW, DVD+RW,
 Special DVD drives are necessary to read information from DVDs.
Fortunately, these drives also read CD-ROMs.
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21. Secondary storage characteristics
 Media ( actual physical material that holds the data and
programs, Example: CD).
 Capacity( measured how much a particular storage medium
can hold)
 Storage devices (are hardware that reads data and program
from storage media)
 Access speed ( measures the amount of time required by
storage device to retrieve data and program).
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22. Output devices
 Output devices display information in a way that you can
understand.
 They are devices that bring information out of a computer.
 Common output formats are
 printed-paper,
 sound,
 video and
 on-screen documents.
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23. Some of the major output devices are:
 Monitors
 Printers
 Plotters
 Speakers
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24. Monitors or Visual Display Units (VDUs):
 It looks a lot a like a TV.
 It produce Soft copy output.
 It allows you to 'see' what you and the computer are doing together.
 It is a device that displays a video signal, similar to a television.
 These are the most common types of Monitors :
Desktop monitors which are also known as Cathode Ray Tube
(CRT)
Liquid Crystal Displays (LCD) which are also known as Thin
Film Transistors (TFT)
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25. Printers
 a peripheral device that produces a hard (usually paper) copy of a
document.
 It takes what you see on the computer screen and prints it on paper.
 There are three types of printers.
 Laser printers: use lasers to print.
 Produce a very high quality output, are very quiet and very fast.
Laser color printers are quite expensive to buy.
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26. Cont.…
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 Ink-jet printers: uses inks to print.
 Offer black and white or color printing with reduced levels of
quality and speed. Color ink jet printers are cheaper to buy than
color laser printers.
 Dot-matrix printers: use hammer to print.
They are comparatively noisy and low quality but are cheap.

27. Plotters
 A plotter can be used to produce high quality, accurate, A3 size or
bigger drawings.
 They are usually used for printing out plans for houses or car
parts.
Speakers
 It allow you to hear sound from your computer.
 It is a device that converts analog audio signals into the
equivalent air vibrations or digital signal in order to make audible
sound.
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28. Factors Affecting a Computer’s Speed
Amount of memory (RAM)
 The more RAM a computer has, the more program instructions and data can be
held in memory
 If a computer does not have enough memory to run a program, it must move data
between RAM and the hard disk frequently.
Processor Speed
 Processor speed represents the number of instructions it can execute per sec.
 The faster a computer's processor is, the more instructions the computer can
execute each second.
 A processor’s speed is measured in Hertz, MHz and GHz .
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29. Cont.….
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Bus Speed
 A bus is a path between the components of a computer.
 Data and instructions travel along these paths.
 The data bus' speed determines how many bits can be
transmitted per second between the CPU and other devices

30. END OF UNIT
TWO
.
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