Is a Term used for organized collections of computer data and instructions.
Computer programs are also usually referred to as computer
Software. A Computer Program is a set of instructions given to the computer to solve
Particular problem. Computer program specify a sequence of operations that
Computer will perform.
Computer Software is further divided into two major categories
- System Software
- Application software
System Software refers to the programs that are responsible for controlling and
Managing the actual operations of the computer hardware. Generally system software
Consists of an operating system and some fundamental utilities such as disk formatters,
Managers, display managers, user authentication (login) and network control
Application Software is used to accomplish tasks specified by the user. Application
May consist of a single program, such as an image viewer or a collection of
Programs (called software package) that work together to accomplish a task. e.g.
Word processors, spreadsheet, database etc.
Organization of Computer
A computer performs the following five major functions:
- Accepts data or instructions from input device
- Stores data
- Processes data as required by the user
- Gives results in the form of output
- Controls all operations inside a computer.
In order to perform above mentioned operations; the computer system is divided
Into three units. These are
- Central processing unit (CPU),
- Memory unit
- Input / Output units
Central Processing Unit (CPU)
He Central Processing Unit (CPU) is generally referred to as the brain of the
Computer. The primary work of CPU is to convert data from Input, process the data and output in useful information that can be used by either user or other
Programs. Central processing unit (CPU) is a highly complex set of electronic
Instructions. It is like a really fast
Calculator that has the ability to recall
Numbers from various locations in
Memory, perform arithmetic and logical
Operations with them, such as addition
Or multiplication, and then store the
All computers must have a
Central processing unit. As Figure 2.3
Shows, the central processing unit
Consists of two main parts: The control
Unit, arithmetic and logic unit. Each part
Has a specific function.
Arithmetic and Logic Unit (ALU)
The Arithmetic and Logic Unit (ALU) consists of electronic circuitry that
Executes all arithmetic and logical operations.
The arithmetic and logic unit can perform the following operations, like:
- Logical Operations
A logical operation is usually a comparison of numbers, letters, or special
Characters. The computer can then take action based on the result of the comparison.
This is a very important capability. It is by comparing that a computer is able to tell,
For example, whether there are available seats on train, whether mobile phone
Customers have exceeded their pre-paid credit limits etc.
Logical operations can test for three conditions:
- Equal-to condition: The arithmetic and logic unit compares two values to
Determine if they are equal. For example, if the number of tickets s d
Equals the number of seats in the hall, then no more tickets are available
Less-than condition: The computer compares values to determine if one
Less than another. For example, if the hours a person worked this week
Are less than 35, then some fine is deducted from his salary.
The computer determines if one value is greater
Than another. For example, if the hours a person worked this week are
Greater than 40, then he gets bonus for working overtime.
Control Unit (CU)
The Control Unit consists of circuitry that generates signals to direct the entire
Computer system to carry out or execute the programs. The control unit itself does not
Execute program instructions; rather, it directs other parts of the system to do so. The
Control unit must communicate with the arithmetic and logic unit, memory and other
Of computer system.
It also controls the flow of information through the processor, and coordinates
Activities of the other units. This unit also provides clock pulses. Clock pulses are
In addition to the ALU and CU (Control Unit), the processor has a number of
Locations to store information that is currently being processed. These are
Registers. These are temporary storage areas for instructions or data. Registers
Managed by the control unit to accept, hold, and transfer instructions or data and
Arithmetic or logical comparisons at high speed.
The CPU must be able to communicate with all devices. The devices are
Together by a communications channel called a bus. A ‘bus is composed of
“f communication lines or wires. It is used to move large amount of bits in the
Electrical pulses from a specified source to a specified destination. The bus is
- Central Processing Unit
* Control Unit
* Arithmetic and Logic Unit
Main memory (RAM, ROM)
- Input / Output Devices
Bus is the common path which is used to send /receive data and commands
To / from CPU and memory and all input / output devices. It is also used to send /
Receive data from secondary storage. The capacity of a bus depends upon the number
Of data lines it contains. Bus with 16 lines can carry 16-bits (2 Bytes) at a time where
Bus with 32 lines can carry 32-bits (4 Bytes) at a time and so on. There are three
Different buses in the computer system.
- Data Bus
- Address Bus
- Control bus
The most common bus is the data bus. A data bus carries data. It is
Electrical path that connects the central processing unit (CPU), memory, input / output
Devices and secondary storage devices. The bus contains parallel group of lines. The
Number of lines in the bus affects the speed at which the data travels between
Different components. Just like the number of lanes on a motorway affect the amount
Of number of lanes on road means more cars can pass through it.
More lines are present in the bus, it can carry more data. E.g. a bus with 16 lines c
Carry 16 bits (2 bytes) and a bus with 32 lines can carry 32 bits (4 bytes) of data.
Busses are designed in such a way that they can communicate with the
Components in an efficient way. In old computers buses were able to carry only on
Byte of data but with the improvement in technology the busses present in todays
Computer can carry multiple bytes at one time thus improving the speed an
Performance of computers.
An address bus carries address information. It is a set of wires similar to the
Data by but it only connects central processing unit (CPU) and memory. Whenever
The processor needs data from the memory, it places the address of data on the address
Bus. The address is carried to the memory where the data from the requested address
Is fetched and placed on the data bus. The data bus carries it to the processor.
The reason for the importance of address bus is that the number of lines in
The address bus determines the maximum number of memory addresses, if an address
Bus has 8 lines, the maximum number of memory locations that can be addressed
Are 28 256. Today’s computers have 32 bit address lines so they can access
4GB (Giga Byte) of memory.
The control bus carries control information from the control unit to the other
Units. The control information is used for directing the activities of all units. The
Control unit directs the transfer of data to the ALU from the memory. This data is
The functioning of other
Units e.g. . Input/output devices, secondary storage etc.,
Computer storage is also referred to as computer memory. Computer
IS used to store programs and data, There are two types of computer memory.
- Main Storage or Main Memory
- Secondary Storage or Secondary Memory
Main memory is accessible directly by the processing unit. RAM is an
Example of main memory. As soon as the computer is switched off the contents of the
Memory are lost you can store and retrieve data much faster with main memory
Compared to secondary memory, the reason is that the main memory is present on
Mother board. Secondary memory such as floppy disks, magnetic disk. Etc. is
Located outside the motherboard. Main memory is more expensive than secondary
Memory. That is why the size of main memory is less than that of secondary memory.
As the storage capacity of the main memory is limited and often it is
Necessary to store hundreds of millions of bytes of data for the CPU to process,
2-refore, additional memory is required in all the computer systems. This memory is
Secondary memory or secondary storage.
Input / Output Devices
A computer is only useful when it is able to communicate with the external
Environment. When we work with the computer, we feed data and instructions
Sough some devices to the computer. These devices are called input devices,
Similarly computer, after processing data and instructions, gives output through some
Devices called output devices. Input/output devices •are also known as peripheral
A port can be defined as a socket that enables an external device such as a
26nter to be attached to the computer”, All communication between a computer and
External devices is the result of properly connected ports. On every computer, a port’s
Connectors are attached to a motherboard. There are three basic types of ports:
- Serial port
- Parallel port
- USB (Universal Serial Bus) port
‘Today’s computers have all these types of ports with each type doing a different
A serial port allows a serial hardware device to communicate with th-
Computer by transmitting one bit of information at a time. Serial devices, such a
Mouse, modems, and keyboards, do not require fast data transmission rates. Serial
Ports often referred to as communications (COM) ports. It is an external port on thx
Back of the computer that attaches directly to the PC’s motherboard. These ports wer
One of the early ports put on computers. Older serial ports also used 25-pir
Connector for their serial port, but most new computers with serial ports feature onh
A parallel port lets an external parallel device communicate with the computer
by transmitting more bits (Such as 8 or 25) of data at a time there fore, it is much faster
Than a serial port. Most devices that send or receive large amounts of data, such as
Printers and scanners, use parallel ports. Parallel ports are often referred to as Line
Printer (LPT) ports. The parallel port is the largest port on the rear of your PC,
Comprising 25 lines that include 17 signal lines and eight ground lines.
USB (Universal Serial Bus) is€ a plug-and-play hardware interface for
Peripherals such as the keyboard, mouse, joystick, scanner, printer and modem. USB
Has a maximum bandwidth of 12 Mbits /sec and up to 127 devices can be attached.
With USB, a new device can be added to the computer without having to
Add an adapter card. It typically is located at the back PC and looks as in the following (sometimes positioned vertically). Sometimes it has the USB symbol next to it.