Computer: Definition A computer is a machine that can be programmed to manipulate symbols. Its principal characteristics are: It responds to a specific set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a program). It can quickly store and retrieve large amounts of data. Therefore computers can perform complex and repetitive procedures quickly, precisely and reliably. Modern computers are electronic and digital. The actual machinery (wires, transistors, and circuits) is called hardware; the instructions and data are called software. All general-purpose computers require the following hardware components: Central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions organized in programs ("software") which tell the computer what to do. Memory (fast, expensive, short-term memory): Enables a computer to store, at least temporarily, data, programs, and intermediate results. Mass storage device (slower, cheaper, long-term memory): Allows a computer to permanently retain large amounts of data and programs between jobs. Common mass storage devices include disk drives and tape drives. Input device: Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer. Output device: A display screen, printer, or other device that lets you see what the computer has accomplished. In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.

1. Types of computers
Prepared by Anju A

2. The personal computer (PC)
 A personal computer is a general-purpose, cost-effective
computer that is designed to be used by a single end-user.
 A desktop PC (Personal Computer) is a computer meant for
a desk or a home, it is not wireless or portable.
 Desktop pc’s have a mouse, a keyboard and a base unit
which includes the computers components.
 Desktops are generally cheaper than laptops and have a
longer life span.
 An example of a Desktop is an Apple Mac.

3. The personal computer (PC)
 In the mid 1960s and into the 1970s, computers
occupied entire rooms and were only affordable
by large universities and enterprises.
 In its earlier days PCs were bulky and expensive.
 In 1981, IBM came into the arena by introducing
its first personal computer, termed as the IBM PC.
The IBM PC rapidly became popular in the market.

4. The personal computer (PC)
 Only a few companies could survive the popularity of IBM
PCs, including Apple, which remained a leading provider
in the PC market.
 Later, other manufacturers adapted to the PC trend
advanced by IBM by developing IBM clones. Clones were
PCs with almost the same configurations as IBM PCs, but
at a lower price. Gradually, IBM lost their dominance in
the PC arena.
 Presently (as of 2011), the realm of PCs is mainly divided
between Apple Macintoshes and PCs from other
manufacturers.

5.  PCs usually consist the following parts:
 Computer case
 Power supply
 Motherboard
 Random access memory (RAM)
 Hard disk(s)
 CD/DVD drives/writers
 Various external devices, such as a visual display,
keyboard, printer and pointing device

7. Laptop
 A laptop is a portable wireless PC, it can do everything a
desktop can do, but it can do it on the move which makes
laptops generally more popular because you can use a
Laptop anywhere in the home.
 Laptops are generally more expensive than desktops and
netbooks.
 Instead of a mouse, laptops have touchpads which is built in
with the integrated keyboard.
 An example of a Laptop is the Dell Inspiron and Apple Mac.

9. Netbook/Notebook
 A Notebook or Netbook, which is what it is
sometimes known as, is a PC that is similar to a
laptop but is cheaper, lighter and a lot small (e.g
small like a notebook)
 Netbooks are great for business men because they
can use them on the move and they can also
easily put them in a brief case or shoulder bag
without taking up too much space.

10.  An extremely lightweight personal computer.
 Notebook computers typically weigh less than 6 pounds and are small enough to fit easily in
a briefcase.
 Aside from size, the principal difference between a notebook computer and a personal
computer is the display screen.
 Notebook computers use a variety of techniques, known as flat-panel technologies, to
produce a lightweight and non-bulky display screen.
 The quality of notebook display screens varies considerably.
 In terms of computing power, modern notebook computers are nearly equivalent to personal
computers.
 They have the same CPUs, memory capacity, and disk drives.
 However, all this power in a small package is expensive. Notebook computers cost about
twice as much as equivalent regular-sized computers.
 Notebook computers come with battery packs that enable you to run them without plugging
them in.
 However, the batteries need to be recharged every few hours.

11. What is a netbook?
 The term "netbook" is a perfect description of the
product: a small laptop PC intended mostly for using
internet-based tools and services -- surfing the web,
running lightweight apps, saving files to the cloud, and so
on.
 Built with less costly components and fewer optional
features, netbooks were designed to be affordable
systems for casual personal or family use, limited-duration
business work, or as an easily portable travel companion.

12. Advantages of a netbook:
 Less costly than most laptops or tablets
 Convenient to hold, carry and pack
 Extremely light weight
 Physical keyboard for email and business apps
 Long battery life (generally)

13. Disadvantages of a netbook:
 Slower processors and less RAM (generally)
 Small screen size
 Limited internal storage
 Keyboard may be smaller than typical ones
 Few peripheral options (DVD drives, etc.)

14. netbooks have some major differences
compared to laptops:
 Processor:
 Netbook processors need to operate within even smaller spaces
than laptop processors, so netbooks typically use low-voltage,
low-power CPUs similar to those used in tablet PCs.
 This limits their cycle times to the range of 1 GHz to 2 GHz and
makes advanced spreadsheet or photo editing programs slower
than on other systems.

15. netbooks have some major differences
compared to laptops:
 Storage:
 To achieve their light weight (typically about 2 lbs.), netbooks
contain much smaller hard drives and, therefore, less storage
space.
 Capacities vary widely, from smartphone-like 32-64 GB models
to ones with 150 GB or more.
 Systems with solid-state drives offer higher capacities but the
cost of the drives pushes them to the upper half of the netbook
price range.

16.  Features:
 Like tablets, netbooks are built to use the internet for accessing
and using remote services, saving data to the cloud, and so on.
So, you won't find a DVD drive on most netbooks.
 There are still multiple ports to attach USB devices, external
monitors, etc., but the number and type of ports typically goes
down along with the price of the system.
 As with most consumer products, if you're willing to pay more,
you can find netbooks with comparatively faster processors, more
storage capacity and additional features such as touch screens,
handles, Bluetooth connectivity, and so on.

18. PDA
 A PDA (Personal Digital Assistant) is a phonelike device
that manages information.
 Most modern PDAs can access the internet and can
operate like phones so they are now commonly know as
Smartphones.
 PDA’s are becoming uncommon mainly because phones
can do all the things PDA’s can do, but they can also do
more.

19. PDA
 A personal digital assistant (PDA), also known as a
handheld PC, is a variety mobile device which functions as
a personal information manager.
 PDAs have been mostly displaced by the widespread
adoption of highly capable smartphones, in particular
those based on iOS and Android.
 PDAs are also called palmtops, hand-held computers and
pocket computers.

20.  Short for personal digital assistant, a handheld device that combines
computing, telephone/fax, and networking features.
 A typical PDA can function as a cellular phone, fax sender, and
personal organizer. Unlike portable computers, most PDAs are pen-
based, using a stylus rather than a keyboard for input.
 This means that they also incorporate handwriting recognition
features. Some PDAs can also react to voice input by using voice
recognition technologies.
 The field of PDA was pioneered by Apple Computer, which introduced
the Newton MessagePad in 1993.
 Shortly thereafter, several other manufacturers offered similar
products.
 To date, PDAs have had only modest success in the marketplace, due
to their high price tags and limited applications.
 However, many experts believe that PDAs will eventually become
common gadgets.

21. GAME CONSOLE

22. GAME CONSOLE
 The purpose of a games console is to play video games.
 Like most modern devices you can now access the
internet, play other types of media (DVD & Iplayers) and
talk with friends.
 An example is the PS3 and the Xbox 360.
 The PS3 and Xbox are 4th generation games consoles.

24. Tablet
 A tablet is a wireless phone-like computer with a touch
screen.
 The touch screen enables you to control the pointer by
moving your finger around the screen, this is instead of
using a mouse.
 You also use a virtual keyboard rather than a physical one.
 Tablets are bigger than PDA’s and Mobile Phone’s and are
more limited to what they can do compared to a Laptop or
Notebook.
 An example of a Tablet is the Ipad.

25. MAINFRAME

27. MAINFRAME COMPUTER
 Are less powerful than super computers but are capable of
great processing speed, multi tasking capability and high
data storage.
 They are used by most banks to process information of
depositors and millions of daily bank transactions.
 Insurance companies use them for their policy holders
database.
 These computers have specialized wiring system and
usually occupies a big room with temperature control.

28.  Mainframe was a term originally referring to the cabinet containing the central
processor unit or "main frame" of a room-filling Stone Age batch machine.
 After the emergence of smaller "minicomputer" designs in the early 1970s, the
traditional big iron machines were described as "mainframe computers" and
eventually just as mainframes.
 Nowadays a Mainframe is a very large and expensive computer capable of
supporting hundreds, or even thousands, of users simultaneously.
 The chief difference between a supercomputer and a mainframe is that a
supercomputer channels all its power into executing a few programs as fast as
possible, whereas a mainframe uses its power to execute many programs
concurrently.
 In some ways, mainframes are more powerful than supercomputers because
they support more simultaneous programs. But supercomputers can execute a
single program faster than a mainframe.
 The distinction between small mainframes and minicomputers is vague,
depending really on how the manufacturer wants to market its machines.

29.  Mainly used by large companies and orgaizations
to perform critical tasks that involve bulk data
processing like transaction processing, census
information, statistical data and so on.
 They consist of extensive input and output
facilities are very stable and dependable and
handle millions of transactions every day.

30. SUPER COMPUTER

32.  Are the most powerful available.
 These computers are high capacity computers
that run continuously and are being used by very
big organizations mostly big corporations and
government institutions.
 Users of super computers include NASA and US
government, some big schools of companies.

33.  Supercomputer is a broad term for one of the fastest
computers currently available.
 Supercomputers are very expensive and are employed for
specialized applications that require immense amounts of
mathematical calculations (number crunching).
 For example, weather forecasting requires a
supercomputer.
 Other uses of supercomputers scientific simulations,
(animated) graphics, fluid dynamic calculations, nuclear
energy research, electronic design, and analysis of
geological data (e.g. in petrochemical prospecting).
 Perhaps the best known supercomputer manufacturer is
Cray Research.

34. supercomputer
 It is used for sensitive and calculation-intensive
work such as scientific research, physical
simulation, climate studies, oil and natural gas
exploration, weather forecasting, quantum
physics etc.

35. WORKSTATION

37. Workstation
 A workstation is a special computer designed for
technical or scientific applications.
 It is a desktop which is larger, consists of a more
powerful processor, greater memory space and
extra ability to do specific kind of work.
 Such a computer is used by programmers, game
developers, video or sound editors and graphic
designers.

38.  It is a type of computer used for engineering applications
(CAD/CAM), desktop publishing, software development, and other
types of applications that require a moderate amount of computing
power and relatively high quality graphics capabilities.
 Workstations generally come with a large, high-resolution graphics
screen, at large amount of RAM, built-in network support, and a
graphical user interface.
 Most workstations also have a mass storage device such as a disk
drive, but a special type of workstation, called a diskless
workstation, comes without a disk drive.
 The most common operating systems for workstations are UNIX and
Windows NT. Like personal computers, most workstations are single-
user computers.
 However, workstations are typically linked together to form a local-
area network, although they can also be used as stand-alone
systems.