Computer Skills 1

Definition of computer:

An automatic electronic device for making calculations or controlling operations that

are expressible in numerical or logical terms.

Functionalities of a computer:
Any digital computer carries out five functions in gross terms:
 Takes data as input.
 Stores the data/instructions in its memory and use them when required.
 Processes the data and converts it into useful information.
 Generates the output
 Controls all the above four steps.

Characteristics of computer:

 High speed
 Accuracy
 Storage Capability
 Diligence
 Versatility

Usage of computers:

 Commercial
 Education
 Entertainment
 Military
 Industry
 Communications

COMPUTER GENERATIONS:

Generation Time- Technology Operating Example

Period System
First Generation 1940s – 1950s Vacuum Tube None Mark1
Second 1950s – 1960s Transistor None IBM 1401,ICL
Generation 1901
Third Generation 1960s – 1970s Integrated Yes IBM 360,
Circuit HP 9810

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Fourth Generation 1970s – Microprocessor Yes IBM PC,

Present Apple
Macintosh
Fifth Generation Present – Artificial Yes Desktops,
Future Intelligence laptops,
tablets,
smartphones,
etc.

Classification of Computers:

Supercomputer
Supercomputer is the most expensive and fastest type of computer that
performs at or near the currently highest operational rate for computers. A Cray
supercomputer is a typical example. These are employed for specialized applications
that require immense amounts of mathematical calculations such as weather
forecasting, nuclear energy research, and petroleum exploration etc.

Mainframe
A mainframe computer supports a vast number of users to work simultaneously
and remotely. These computers are very large in size, and expensive. The main
difference between a supercomputer and a mainframe is that a supercomputer can
execute a single program faster than a mainframe, whereas a mainframe uses
its power to execute many programs concurrently. The IBM 370 and IBM 3090 are
examples of mainframe computers.

Minicomputers

A minicomputer is powerful enough to be used by multiple users (between 10 to

100) but is smaller in size and memory capacity and cheaper than mainframes. Two
classic examples were the Digital Equipment Corporation vAX and the IBMAS/400.

Microcomputers
The microcomputer has been intended to meet the personal computing needs of
an individual. It typically consists of a microprocessor chip, a memory system,
interface units and various I/O ports, typically resided in a motherboard.
There are many types of microcomputers available.
Desktop computer A microcomputer sufficient to fit on a desk.
Laptop computer A portable microcomputer with an integrated screen and
keyboard.
Palmtop computer/Digital diary/Notebook/PDAs A hand sized microcomputer
having no keyboard. The screen serves both as an input and output device.

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A computer system:

A computer system can be divided into two components which are responsible for
providing the mechanisms to input and output data, to manipulate and process data,
and to electronically control the various input, output, and their storage. They are
known as hardware and software. The hardware is the tangible parts of the
computer. Whereas, the software is the intangible set of instructions that control
the hardware and make it perform specific tasks. Without software, a computer is
effectively useless.

Hardware
Hardware is the physical components of a computer that includes all mechanical,
electrical, electronic and magnetic parts attached to it. A computer consists of the
following major hardware components:
Input and output devices
Central processing unit (CPU)
Memory unit and storage devices
Interface unit

Input Unit(input devices)

This unit contains devices with the help of which we enter data into computer. This
unit makes link between user and computer. The input devices translate the
information into the form understandable by computer.

 Keyboard , Joy Stick , Light pen , Track Ball , Mouse , Scanner , microphone

Output Unit(output devices)

Output unit consists of devices with the help of which we get the information from
computer. This unit is a link between computer and users. Output devices translate
the computer's output into the form understandable by users.

 Monitor , Printer , speaker

CPU (Central Processing Unit)

CPU is considered as the brain of the computer. CPU performs all types of data
processing operations. It stores data, intermediate results and instructions
(program).It controls the operation of all parts of computer.
The CPU itself can be divided into different functional units which are described
below:

registers These are high-speed storage devices. In most CPUs, some registers
are reserved for special purposes. For example, the Instruction Register (IR) holds
the current instruction being executed. The Program Counter (PC) is a register that
holds the address of the next instruction to be executed.

Arithmetic logic unit (ALU) It is the part of the CPU that performs arithmetic
operations, such as addition and subtraction as well as logical operations, such as
comparing two numbers to see if they are the equal or greater or less.

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Control unit (Cu) The control unit coordinates the processing by controlling the
transfer of data and instructions between main memory and the registers in the CPU.
It also coordinates the execution of the arithmetic logic unit (ALU) to perform
operations on data stored in particular registers.

Nowadays, a high-speed memory, called cache memory, is embedded with the CPU
chip. This improves the computer performance by minimizing the processor need to
read data from the slow main memory.

Memory unit:
A storage area is needed in a computer to store instructions and data, either
temporarily or permanently, so that subsequent retrieval of the instructions and data
can be possible on demand. Data are stored in memory as binary digits, called
bits. Data of various types, such as numbers, characters, are encoded as series of
bits and stored in consecutive memory locations. There are mainly two types of
memory that are used in a computer system. One is called primary memory and the
other secondary memory.

Primary memory:

Primary memory is the area where data and programs are stored while the
program is being executed along with the data. This memory space, also known
as main memory, forms the working area of the program. This memory is accessed
directly by the processor.

There is another kind of primary memory increasingly being used in modern

computers. It is called cache memory (pronounced as “cash”). It is a type of high-
speed memory that allows the processor to access data more rapidly than from
memory located elsewhere on the system. It stores or caches some of the contents
of the main memory that is currently in use by the processor.

All modern computers use semiconductor memory as primary memory. One of the
important semiconductor memories used in desktop computers is Random Access
Memory (RAM). Here “random access” means that any storage location can be
accessed (both read and write) directly. This memory is faster, cheaper, and provides
more storage space in lesser physical area.

The only drawback of semiconductor memory is that it is volatile, i.e., it loses its
contents whenever power is switched off. RAM holds the data and instructions waiting
to be processed by the processor. In addition to data and program’s instructions,
RAM also holds operating system instructions that control the basic functions of a
computer system. These instructions are loaded into RAM every time the computer is
turned on, and they remain there until the computer is turned off. There are two
types of RAM used in computer systems– dynamic and static.

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There are several popular types of dynamic RAM used in computers. They are SDRAM
(Synchronous Dynamic RAM), RDRAM (Rambus Dynamic RAM) and DDR RAM
(Double Data Rate RAM).

Read Only Memory (ROM)

It is another type of memory that retains data and instructions stored in it even when
the power is turned off. ROM is used in personal computers for storing start-up
instructions provided by the manufacturer for carrying out basic operations such as
bootstrapping in a PC, and is programmed for specific purposes during their
fabrication. ROMs can be written only at the time of manufacture.

Types of ROM:

Programmable ROM (PROM), is also non-volatile and can be programmed only

once by a special device.

EPROMs (Erasable Programmable Read Only Memories).

Electrically Erasable Programmable Read Only Memory (EEPROM)

Secondary memory:

Secondary memory provides large, non-volatile, and inexpensive storage for

programs and data. However, the access time in secondary memory is much larger
than in primary memory. Secondary storage permits the storage of computer
instructions and data for long periods of time. Moreover, secondary memory, which is
also known as auxiliary memory, stores a huge number of data bytes at a lesser cost
than primary memory devices.

There are four main types of secondary storage devices available in a computer
system:
Disk drives, CD drives (CD-R, CD-RW, and DvD) , Tape drives , USB flash drives

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Unit of Memory:

The memory’s interface circuit is designed to logically access a byte or a multiple of a

byte of data from the memory during each access. The smallest block of memory
is considered to be a byte, which comprises eight bits. The total memory space
is measured in terms of bytes. Thus, the unit of memory is a byte. The capacity of
memory is the maximum amount of information it is capable of storing. Since
the unit of memory is a byte, the memory’s capacity is expressed in number of bytes.
Some units used to express the memory capacity are as follows:
Kilobyte (KB) = 1024(210) bytes(B)
Megabyte (MB) = 1024(210) KB = 220 B
Gigabyte (GB) = 1024(210) MB= 220 KB= 230 B
Terabyte (TB) = 1024 (210) GB= 220 MB= 230 KB =240 B
Petabyte (PB) = 1024 (210) TB= 220 GB= 230 MB =240 KB =250 B
Exabyte (EB) = 1024 (210) PB = 220 TB= 230 GB =240 MB =250 KB =260 B
Zettabyte (ZB) = 1024(210) EB = 220 PB= 230 TB =240 GB =250 MB =260 KB =270B
Yottabyte (YB) = 1024 (210) ZB= 220 EB= 230 PB =240 TB =250 GB =260 MB =270 KB
=280 B

Memory hierarchy The various types of memory used in a computer system differ
in speed, cost, size, and volatility (permanence of storage). They can be
organized in a hierarchy. The memory hierarchy in the computer system is depicted
in Fig below:

Interface unit:
The interface unit interconnects the CPU with memory and also with the various
input/output (I/O) devices. The instructions and data move between the CPU and
other hardware components through interface unit. It is a set of parallel wires or
lines which connects all the internal computer components to the CPU and main
memory. Depending on the type of data transmitted, a bus can be classified into the
following three types:
Data bus The bus used to carry actual data.

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Address bus memory or Input/output device Addresses travel via the address
bus.
Control bus This bus carries control information between the CPU and other devices
within the computer.

Motherboard
All the components in the computer system are mounted and connected together by
an electronic circuit board called motherboard or main board.
To make all these things work together the motherboard provides some kind of
physical connection among them. (See Fig below)

System unit
The System Unit holds all the system components in it. It is sometimes called
cabinet. The main components like motherboard, processor, memory unit, power
supply unit, and all the ports to interface computer’s peripherals. Inside the unit all
the components work together to give the service that the user needs. Based on its
use, cabinets are of two types.
(i) AT cabinets (or mini-tower)
(ii) ATX cabinets

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AT cabinets are smaller and cheaper than ATX cabinets and are popularly called
mini-tower cabinets. They are used for older processors and smaller motherboards.
ATX cabinets, on the other hand, are marginally larger in size than AT cabinets and
are more expensive as they come with more features such as powered sliding front
panels and extra disk storage compartments.

Software
Software provides the instructions that tell the hardware exactly what is to be
performed and in what order. This set of instructions is sequenced and organized in a
computer program. Therefore, a program is a series of instructions which is intended
to direct a computer to perform certain functions and is executed by the processor.
In a broader sense, software can be described as a set of related programs.

Software is generally categorized as system software or application

software or utility software.

System software
System software is designed to facilitate and coordinate the use of the computer by
making hardware operational. It interacts with the computer system at low level.
Examples of such software include language translator, operating system, loader,
linker, etc.

Application software
Application software is designed to perform specific usages of the users. Microsoft
Word, Microsoft Excel, Microsoft Power Point, Microsoft Access, Page Maker, Coral
Draw, are some of the examples of application software. There are two categories of
application software, custom software and pre-written software packages.
Software that is developed for a specific user or organization in accordance with the
user’s needs is known as custom software.
A pre-written software package is bought off the shelf and has predefined generic
specifications that may or may not cater to any specific user’s requirements. The
most important categories of software packages available are as follows:

*Database management software, e.g. Oracle, DB2,

*Microsoft SQL server, etc.

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*Spreadsheet software, e.g. Microsoft Excel.

*Word processing, e.g. Microsoft Word, Corel Wordperfect and desktop
publishing (DTP), e.g. Pagemaker.
*Graphics software, e.g. Corel Draw.
*Statistical, e.g. SPSS and operation research software, e.g. Tora.

Operational Overview of a CPU:

Any processing executed by central processing unit is directed by the instruction. The
processing required for a single instruction is called an instruction cycle. The four
steps which the CPU carries out for each machine language instruction are fetch,
decode, execute, and store The steps involved in the instruction cycle while
executing a program are described below.
The Program Counter (PC) is the register that keeps track of what instruction
has to be executed next. At the first step, the instruction is fetched from main
memory and loaded into Instruction Register (IR), whose address is specified by
PC register. Immediately the PC is incremented so that it points to the next instruction
in the program. Once in IR, the instruction is decoded to determine the actions
needed for its execution. The control unit then issues the sequence of control signals
that enables execution of the instruction. Data needed to be processed by the
instructions are either fetched from a register from RAM through an address register.
The result of the instruction is stored (written) to either a register or a memory
location. The next instruction of a program will follow the same steps. This will
continue until there is no more instruction in the program or the computer is turned
off, some sort of unrecoverable error occurs.

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