1. What is Computer?
Computer is an electrical machine which accepts data and figures and after processing provides
correct information.
Computer is an electrical machine that can solve a no of problem in seconds.
Components of Computer
1. Hardware
2. Software
Hardware
All those part of computer system which can be seen and touched are called hardware. For example
Keyboard, Mouse, CPU, Speaker, Monitor etc.
Two parts of hardware
1. Input Hardware
2. Output Hardware
Input  Processing  Output
Input
All the fact and figures given to the computer for processing is called input
Input Devices
All devices which are used to enter data in the computer are called input devices.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Mouse
Keyboard
Scanner
Micro phone
Digital camera
Joy stick
Trac ball
Bar Code Reader
Light Pen
Touch Screen
1. Mouse
This is a pointing device which contains a roller in its base. When the mouse is moved on any surface,
the pointer on the screen is also moved.
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2. 2. Keyboard
This is most commonly used device which acts as input device. Its structure is like typewriter.
Used for typing document applications.
3. Scanner
The scanner is an input device like the photocopier machine which makes the electronic copy of the
picture or document
4. Microphone
An instrument that converts sound waves into an electric current, usually fed into an amplifier, a
recorder. That used to enter sound in a computer.
5. Digital Camera
A camera that records and stores digital images.
6. Joy Stick
A joystick is a cursor control device used in computer games.
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3. 7. Track ball
A trackball is a computer cursor control device used in many notebook and laptop computers. The
trackball is usually located in front of the keyboard toward the user.
8. Bar Code Reader
It is a device which is used to read the code from the products
which are usually in the form of Bars. It contains a light sensitive
detector which identifies the values of the bars on the product &
converts them into numeric code.
9. Light Pen
It is a pointing device which contains a photocell mounted at its
tip. It senses the light from the screen when it becomes closer to
the screen, & generates a pulse. So for identifying a particular
location on the screen these light pens are very useful.
10. Touch Screen
A touch screen is a computer screen or other screen that you can touch with your finger to enter
information. Examples of touch screens include a smart board, a microwave, a dishwasher, or an ATM
at a bank.
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4. Output
The information obtain from computer after processing is called output
Output Devices
All those devices which are used to obtain information from the computer are called output devices.
1. Monitor
2. Speaker
3. Printer
1. Monitor
A computer monitor is defined as being a piece of electrical equipment that displays images without
producing a permanent record. A monitor consists of the display device, electronic circuitry, and a
case that it all goes into. Computer monitors can be CRT, LCD, or Plasma.
2. Speaker
Speakers are popular output devices used with computer systems. They receive audio input from the
computer's sound card and produce audio output in the form of sound waves. Most computer speakers
are active speakers, meaning they have an internal amplifier which allows you to increase the volume,
or amplitude, of the sound.
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5. 3. Printer
A printer is a device that accepts text and graphic output from a computer and transfers the
information to paper, usually to standard size sheets of paper. Printers are sometimes sold with
computers, but more frequently are purchased separately. Printers vary in size, speed, sophistication,
and cost. In general, more expensive printers are used for higher-resolution color printing.
Software
All those part of a computer which can be seen but not touched are called software. For example
Windows.
Proper definition of software
A set of instructions given to the computer for specific purpose is known as software.
Parts of software
1. System/Operating Software
2. Application Software
1. System & Operation software
The software which is necessary to run or operate a computer system are called operating or system
software such as
Dos
Windows
Linux etc.
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6. 2. Application Software
The software which is not necessary to run or operate a computer system but it is used for user
application and requirement are called application software such as
Ms. Office
Typing Master
In page
Games etc.
Types of Computer
Computer types can be divided into 3 categories according to electronic nature. Types of
computers are classified according to how a particular Computer functions. These computer
types are
· Analogue Computers
· Digital Computers
· Hybrid Computers
Analogue Computers
Analogue types of Computer uses what is known as analogue signals that are represented by a
continuous set of varying voltages and are used in scientific research centers?, hospitals and
flight centers
With analogue types of computer no values are represented by physical measurable quantities
e.g. voltages. Analogue computer types program arithmetic and logical operations by measuring
physical changes i.e. temperatures or pressure.
Digital Computer type
With these types of computers operation are on electrical input that can attain two inputs, states
of ON=1 and state of OFF = 0. With digital type of computers data is represented by digital of 0
and 1 or off state and on state. Digital computer type recognizes data by counting discrete signal
of (0 0r 1), they are high speed programmable; they compute values and stores results. After
looking at the Digital computer type and how it functions will move to the third computer type as
mentioned above.
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7. Hybrid type of Computer
Hybrid computer types are very unique, in the sense that they combined both analogue and
digital features and operations. With Hybrid computers operate by using digital to analogue
convertor and analogue to digital convertor. By linking the two types of computer above you
come up with this new computer type called Hybrid.
Classification of Computer’s on the base of size & power
Computers can be generally classified by size and power as follows, though there is considerable
overlap:
Supercomputer:
An extremely fast computer that can perform hundreds of millions of instructions per second.
Mainframe:
A powerful multi-user computer capable of supporting many hundreds or thousands of users
simultaneously.
Minicomputer:
A multi-user computer capable of supporting up to hundreds of users simultaneously.
Workstation:
A powerful, single-user computer. A workstation is like a personal computer, but it has a more
powerful microprocessor and, in general, a higher-quality monitor.
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8. Personal computer:
A small, single-user computer based on a microprocessor.
Personal Computer Types
Tower model
The term refers to a computer in which the power supply, motherboard, and mass storage devices
are stacked on top of each other in a cabinet. This is in contrast to desktop models, in which
these components are housed in a more compact box.
Desktop model
A computer designed to fit comfortably on top of a desk, typically with the monitor sitting on top
of the computer. Desktop model computers are broad and low, whereas tower model computers
are narrow and tall. Desktop models designed to be very small are sometimes referred to as slim line
models.
Notebook computer
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.
Laptop computer
A small, portable computer -- small enough that it can sit on your lap. Nowadays, laptop
computers are more frequently called notebook computers.
Subnotebook computer
A portable computer that is slightly lighter and smaller than a full-sized notebook computer.
Typically, subnotebook computers have a smaller keyboard and screen, but are otherwise
equivalent to notebook computers.
Hand-held computer
A portable computer that is small enough to be held in one’s hand. Although extremely
convenient to carry, handheld computers have not replaced notebook computers because of their
small keyboards and screens. The most popular hand-held computers are those that are
specifically designed to provide PIM (personal information manager) functions, such as a
calendar and address book.
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9. What is C.P.U (Central Processing Unit)
The Central Processing Unit (CPU), also known as CPU, is the main
processing chip of a computer. This chip processes the information that the
various components in the computer pass to it. In current times the speed of
the CPU is rated in MHz or Hz. For example 760MHz and 2.40GHz.
Types of CPU
The Central Processing Unit (CPU) has 2 parts, the Control Unit(CU) and the Arithmetic Logic Unit
(ALU)
1) Arithmetic Logic Unit (ALU)
Its divided into two parts AU (Arithmetic unit) and LU (Logic Unit)
AU (Arithmetic unit)
Its performed all mathematical operations such as (+,-,*,/) For example 2+2=4, 5*2=10
LU (Logical unit)
Its tell us the answer is true or wrong. For example 2+2=4 True and 5*2=7 Wrong.
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10. 2) Control Unit (CU)
Its control and manage all the process performed in CPU and Can execute or store the results coming
out of the ALU.
Computer Storage Devices
 Primary Storage Devices
 Secondary Storage Devices
Primary Storage Devices
Internal memory and main memory, primary storage is a storage location that holds memory
for short periods of times while the computer running. For example, computer RAM and ROM
are both examples of a primary storage device.
 ROM (Read only Memory)
 RAM (Random Access Memory)
ROM (Read only Memory)
Short for Read-Only Memory, ROM is a type of "built-in"
memory that is capable of holding data and having that data
read from the chip, but not written to. Unlike Random
Access Memory (RAM), ROM is non-volatile which means
it keeps its contents regardless if it has power or not. A good
example of ROM is EEPROM, which is a programmable
ROM used for the computer BIOS, as shown in the example
picture to the right.
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11. RAM (Random Access Memory)
RAM is an acronym for random access memory, a type of computer memory that can be
accessed randomly; that is, any byte of memory can be accessed without touching the preceding
bytes. RAM is the most common type of memory found in computers and other devices, such as
printers.
Ram is a temporary memory all programs are loading in ram and then display. If computer is off
all data running in ram is loss
.
Types of RAM
There are two different types of RAM:


DRAM (Dynamic Random Access Memory)
SRAM (Static Random Access Memory).
The two types of RAM differ in the technology they use to hold data, with DRAM being the
more common type. In terms of speed, SRAM is faster. DRAM needs to be refreshed thousands
of times per second while SRAM does not need to be refreshed, which is what makes it faster
than DRAM.
DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as
10 nanoseconds. Despite SRAM being faster, it's not as commonly used as DRAM because it's
so much more expensive.
Secondary Storage Devices





Store most of the information the computer uses
Locate outside the primary storage area
Non-volatile
Retains data even when the computer is turned off
Used for relatively long term storage of data out side the CPU
1.
2.
3.
4.
5.
6.
7.
Disk drive
Hard disk
Floppy disk
Magnetic Taps
CD (Compaq disk) or Optical Disk
DVD (Digital Video Disk)
USB/ Flash Memory
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12. 1) Disk Drive
 The device in which the disk is made rotating
 Reads data from or writes them onto the disk
 Reading or writing is done via read/write heads
2) Hard Disk
 The main secondary storage device of a
computer system.
 Available in 40 GB, 80 GB, 320 GB,500GB
and even more capacities.
 Composed of a pack of disks mounted on to
the disk drive.
 There is one read write head per each
surface.
3) Floppy Disk
 Can be insert into and remove from its drive whenever needed
 Can be used
 For transferring data from computer to computer.
 As a backup media The size of today’s most popular type.


Length and width (both) = 3.5 inch
Capacity
= 1.44 MB
 Not reliable and easily damageable.
 . Used in desktop and laptop computers.
 Storage capacity and the access rates are lower than hard disks.
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13. 4) Magnetic Taps
 An older storage technology.
 Still employed for secondary storage of large
quantities of data, needed rapidly but not
instantly.
 Relatively very inexpensive and stable.
 Stores data sequentially.
 Relatively very slow compared to other
secondary storage media.
5) CD (Compaq disk) or Optical Disk




Also called compact disks.
Store massive quantities of data in a highly compact form.
Available for both PCs and large computers.
A 4.75-inch compact disk for PCs can store up to 700
MBs of data.
 Nearly 500 times more than the capacity of a high-density
floppy diskette.
 They are also suitable for applications combining text,
sound, and image.
6) DVD (Digital Video Disk)
 Digital video disks (DVDs), are optical disks having the
same size as CD-ROMs but of even higher capacity.
 Can hold a minimum of 4.7 GBs of data.
 DVDs are enough to store full length, high quality motion
pictures, movies and multimedia applications.
7) USB( Universal Serial Bus) or Flash Memory
 The flash drive is removable and portable.
 The drive and the storage device both are compactly built into a single small unit.
 Available in 1 GB, 2 GB, 4 GB, 8 GB, 16 GB or even more .

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14. Storage measuring units
 8 bits
 1024 bytes
 1024 KB
 1024 MB
 1024 GB
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1 Byte
1 Kilo byte (KB)
1 Megabyte(MB)
1 Gigabyte (GB)
1 Terabyte (TB)
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15. System Buses
A bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can be
shared by multiple hardware components in order to communicate with one another.
The purpose of buses is to reduce the number of "pathways" needed for communication between
the components, by carrying out all communications over a single data channel. This is why the
metaphor of a "data highway" is sometimes used.
There are three types of system buses.
1. Data Bus
2. Address Bus
3. Control Bus
1. Data Bus
A bus which carries data from one part of computer to another part is caller data bus
2. Address Bus
A bus which carries address at which the data needs to be placed is called address bus
3. Control Bus
A bus which helps the control unit to control all the functions and operation of the computer is
called control bus.
Bus Throughput
To get the total throughput capability of the bus, multiply the bus clock speed in hertz
times the number of bits 'wide' the bus is. Data Busses are almost always a multiple of 8
bits wide (8, 16, 32, 64 etc.)
For instance:
33 MHz x 32 bits = 1,056 mbps/sec
200 MHz x 64 bits = 12,800 mbps/sec (12.8 gbps)
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