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Introduction to Computer

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The word “Computer” is derived from the word “compute” which means to calculate. In the past, the computer was normally considered to be a calculating device used to perform arithmetic operations. But today, computer is used in every field of daily life to solve problems of different kinds. So computer can be defined as:

“Computer is a modern electronic machine that is used to solve different kinds of problems according to a set of instructions given to it.”

A computer can perform the following functions:-

➢ Accepts data and instructions as input

➢ Processes or manipulates the data according to the given instructions

➢ Produces results known as output

➢ Stores results for later use

➢ Retrieves results or information when required

Today, computer is playing very important role in every field of life. Small computers are also fitted (embedded) into many other electronic devices such as mobile phones, toys, microwave ovens and MP3 players etc.


Data & Information

The word ‘data’ refers to facts concerning things, people, objects, events etc. Therefore, a collection of raw facts and figures is called data. The word ‘raw’ means unprepared or unprocessed. Data can also be defined as: “an unarranged, unprocessed and meaningless fact about an entity is called data.” Data may consist of text, numbers, images, audio, and video. Data is collected for different purposes. It does not give clear and proper meanings. So it cannot be used directly for decision-making.

A list of class students, showing students roll numbers, names, obtained marks etc. is an example of students’ data.

Suppose four students in a class who have appeared in an examination. The names and marks obtained by students are shown below.

Aqsa          62             63            64

Barira       50            75             70

Hadia        90            80             70

Rashid       75           80             60

The above list of names and numbers represent data of students. This data is in raw form. It does not convey the proper meaning.


The processed data is called information. The processed data (information) gives clear and proper meanings. So it can be used for decision-making.


Data processing

A process to convert data into information is called data processing. Different operations are performed on data to convert it into useful information. These operations may include arithmetic data sorting and data formatting etc.

Data can be processed manually or by using computer. Today, data is processed using computer. Data and instructions are given to the computer. It processes data according to the given instructions and converts it into required information or results. Suppose the above data of four students is processed to get the information as follows:

Result Sheet of Class Student

Sr.No Name English Chemistry Computer Total
1 Aqsa 61 65 66 192
2 Barira 74 58 79 211
3 Hadia 82 73 71 226
4 Rashid 78 86 76 240


The above processed data conveys the clear and proper meaning.

Levels of Data Processing

The data processing is divided into three categories or levels:

  • Manual Data Processing
  • Mechanical Data Processing
  • Electronic Data Processing


  1. Manual Data Processing

In manual data processing, data is processed manually without using any machine or tool. All types of calculations and other operations are performed by human beings. Similarly, data is manually transferred from one place to another. This method of data processing is very slow and errors may occur in the output. This type of data processing was used before the invention of computer and other machines. In Pakistan, data is still processed manually in many small business firms as well as government offices and institutions.

Example: A clerk in a college performs following tasks by hand at the end of month on his register with the pen:


Information Processing cycle (IPC)

Different activities are performed in data processing to convert data into information. Data and instructions are given to a computer. Computer processes into date according to given instructions and converts it into information. Data is the input while information is the output of data processing. A computer often stores data information, and instructions for later use. “A series of steps used to convert data into useful information is known as information processing cycle”.

Different steps in information processing cycle are as follows:

  • Input: In this step, a computer accepts data and instructions via input device such as keyboard or mouse or scanner.
  • Processing: In this step, a computer converts data into information according to the given instructions (It means computer processes data).
  • Output: In this step, a computer provides the results to the users through output device such as monitor or printer.
  • Storage: In this step, a computer stores results permanently on storage devices such as hard disk or CD/DVD or USB flash memory.


Cloud Computing

The delivery of computing services over the Internet is called cloud computing. These services include storing, managing, processing and accessing data online. Companies offering these computing services are called cloud providers. We can use these services (cloud computing) instead of buying and installing our own computer system.

Cloud computing consists of a front-end and a back-end, connected to each other through a network. The front-end consists of hardware and software through which a user interacts to access the cloud. For example, a user might access resource on the cloud through a browser on smart phone or laptop computer. The back-end consists of the servers and storage devices that manage and store data and applications (resources) accessed by the users.



A system that enables engineers and architects to design models of the pr ducts, new vehicles, aircrafts, bridges, buildings and many other things is called Computer-Aided Design (CAD). It is a combination of hardware and software.

CAD system allows engineers / architects to view a designed model from any angle. The designed model can be changed/ modified very easily. When an engineer changes one value, all other values that depend on it are automatically changed accordingly.


Computer-Aided Manufacturing (CAM)

A system that is used to control the machine tools and related machinery in manufacturing process of the product is called Computer-Aided manufacturing (CAM). It is a combination of hardware and software. In this system, computers control all steps of the product manufacturing. Often, robots carry out processes in a CAM environment. CAM is used in different industries, including oil drilling power generation, food production, and automobile manufacturing. For example, in an automobile plant, robots are used for assembling cars.

CAM system has the following benefits:

* Product can be made very accurately and quickly.

* Product design can be modified very easily.

* It requires small number of persons for labor in the production manufacturing process.

* Produced product is much cheaper.


Computer-Integrated Manufacturing (CIM)

A computer-automated system that controls all activities/functions related to designing and manufacturing of products is called computer integrated manufacturing (CIM).

Computer Integrated Manufacturing includes different combinations oil, such as Computer Aided Design (CAD), Computer Aided Engineering (CAE), Computer Aided Manufacturing (CAM), robotics, and Manufacturing Rest Planning (MRP-II). Its objective is to streamline the manufacturing processes and to integrate them with other business functions (such as accounting, financing, distributing, marketing).

The heart of computer integrated manufacturing is CAD/CAM technology. This technology has been applied in many industries for designing manufacturing of products. CAD makes use of computer systems in creation, modification, analysis and optimization of design.



Representation and manipulation of graphics through the use of computer system is known as computer graphics. The combination of picture, images, text & colors that gives any type of information is called graphics. Computer-graphics system is used for creating and manipulating graphics. It consists of computer hardware and software:

Computer hardware includes a computer, various input and output devices. The mouse, scanner, light pen, digital camera etc. are input devices that help for drawing and entering image/graphics data into computer. The graphics monitors, laser printer /inkjet printer, plotters etc. are output devices that help for displaying and printing graphics.

Computer software includes graphics packages/applications that enable a computer to process graphics. Many graphics packages /applications are available that are used to draw and manipulate images. All CAD/CAM systems support graphics. Many software applications also include graphics components. For example, most of the word processors support graphics because they provide feature to draw or import pictures.



A computer simulation is a special type of computer model or program, used to represent the real world system. In other words, computer simulation is artificial system, which represents the working of an actual system. Simulations often used to train the people or students when:

* is impossible to build a system due to economic problems.

* Direct experimentation is impossible in real life due to dangerous system

* System is not available in real time.



The computer has changed our society today as the industrial revolution changed society in the eighteenth and nineteenth centuries. Computer has affected all aspects of people’s lives. It has become a need in our daily activities. Like other electronic devices at home, computers also have become need of every person, for entertainment as well as to perform jobs very quickly.

In the twentieth century, mobile phone and television progressed in the field of communications. In this century, computer has changed the style of our daily activities. In near future, we shall totally depend upon this machine (i.e. computer). Today in Europe, most of the systems are controlled by the computers. In the near future, the advancement in computer technology will occur in the following areas:

* Hardware * Software * Communications and networks * Robotics



Computer is playing a vital role in today’s modem world. The field of information technology is offering great opportunities of jobs to IT-skilled people. There are many careers in IT which can be adopted by the computer professionals (or IT professionals). Different IT careers are discussed as under:

System Analyst

A person who analyzes a complex process or operation in order to improve its efficiency, especially by applying a computer system is called system analyst. He/she is specializes in analyzing, designing and implementing information systems or computer systems.

A system analyst selects and configures computer systems for an organization or business. He/she must understand the general objectives of the organization as well as what each individual user’s job requires. Once the system analyst has determined the general and specific needs of the organization, he/she can choose appropriate system that will help to accomplish the goals of the business.


Computer Programmer

A person who writes software code is called computer programmer. Computer programmer is also known as software developer or coder. He/she writes software code on the basis of system’s analysis and design. He/she tests and debugs the software code. He/she also modifies the software code to meet the new requirements of the users or organization.


Software Engineer

A person who applies the software engineering principles to design, develops, maintenance and testing software is called software engineer. He/she also applies software engineering principles to all the systems -where there is any role of information technology.


Web Designer

A person who designs, develops and modifies websites is called designer. He/she is an IT professional. He/she is involved with the technical and graphical aspects of a website; how the website works and how it looks. He/she also be involved with the maintenance and update of an existing website. The designer must have good knowledge about modern web programming languages and web development tools.


Multimedia Designer

A person who produces multimedia products such as animation, audio, text and graphics etc. is called multimedia designer. Multimedia products are mostly used ill video games, websites and many other interactive applications.


Input/ Output Register (I/O)

Input/output register is used to communicate with the input/output devices. The data and instructions from input devices are first transferred to this register. Similarly, information is transferred to output devices through this register.


Stack Control Register

A stack represents a set of memory blocks. The data is stored in and retrieved from these blocks in an order. This order is called Last In and First Out (LIFO). Stack control register is used to manage the stacks in memory. For example, undo and redo operations in different application software are managed by stack. Stack control register is also known as stack pointer register.


Flag Registers

Flag registers are used to indicate occurrence of a certain condition during an operation of the CPU. Some flag registers are Zero flag, Carry flag, Parity flag, Overflow flag and Sign flag. The size of a flag register is one byte or two bytes. Each byte of a flag register is further divided into eight bits. Each bit of the flag register indicates a flag or condition. For example, if zero value is put into an arithmetic register (accumulator) as a result of an arithmetic operation or a comparison then the zero flag will be raised by the CPU.



A processor contains small, high-speed storage locations. These storage locations are called registers. The registers are used during program execution. They temporarily hold instructions, data, or intermediate results of calculations. The size of these registers is 2 or 4 or 8 bytes. The large sizes of registers increase the performance of CPU. For example, a computer having 32-bit (4-bytes) registers means the CPU can process four bytes of data at a time.

A processor has different types of registers. Each register is used for a specific purpose. Following are the main functions of registers:

* Storing the location of instruction from where it was fetched from memory.

* Storing an instruction while the control unit decodes it.

* Storing the results of a calculation.


Memory Buffer Register (MBR)

Memory Buffer Register (MBR) holds the contents of data or instruction red e from, or written in memory. It means that this register is used to store data/instruction coming from the memory or going to the memory.


Program Counter (PC)

Program Counter register controls the sequence in which the instructions are fetched from the n,, awry. It holds the address of the next instruction to be fetched for execution. Contents of PC are loaded into MAR to fetch an instruction from memory. After fetching an instruction from memory, the value of PC is incremented. After the instruction is fetched, PC points to the next instruction in the sequence. Thus this register always points or holds the address of next instruction that is to be fetched. This register is also known as Instruction Pointer Register’s


General-Purpose Registers

General-purpose registers of CPU store data (operands), addresses of data and intermediate results of operations. These registers are used for arithmetic and logical operations on data and for data movement from one part of the computer to the other. These registers are the part of ALU. The important general-purpose registers are as follows:

Accumulator Register (AC)

The accumulator register is used during arithmetic & logical operations of ALU. This register holds the initial data to be operated upon, the intermediate results, and the final result of operation. The final result is transferred to main memory through MBR. Modern computer systems often have multiple general purpose registers that operate as accumulators, and the term is no longer as common as it once was. However, a number of special-purpose processors still use a single accumulator for their work, in order to simplify their design.


Processor Cooling

When a processor is working, it also generates small amount of heat. This heat may burn up the processor chip. In a system unit, a cooling system is used for providing proper cooling to the processor. It may consist of heat sink, cooling fat heat pipe, and liquid cooling system. Today, in many PCs heat sink is used to absorb heat generated by processor chip. Heat sink is a small ceramic or metal component. It is installed on the top or side of the processor chip. In some processors, heat sinks are built in the processor chips. Heat pipe is another component, which is also used to absorb heat. Its size is smaller than heat sink. It is normally used in notebook computers.

Small mobile computers and devices use very low voltage to operate. The processor chips of these computers or devices do not require additional cooling system.


Instruction Register (IR)

Instruction register stores the recently fetched instruction from the memory for execution. The control unit decodes the instruction in this register and executes it by sending control signals to the appropriate component of computer to carry out the task.

Memory Address Register (MAR)

Memory Address Register holds the address of memory where CPU wants to read or write data. When CPU wants to store some data in the memory or reads the data from the memory, it places the address of the required memory location in the MAR.



System Clock

It generates regular electronic pulses or ticks. It is just like your heart. It controls timing of all computer known as heart of the computer. It controls the functions of the computer using – ticks/pulses.

System clock can generate pulses/ticks from millions to billions per second. Each tick or pulse is known as clock cycle. The clock speed is measured by the number of clock cycles or ticks per second. In the past, processors used on or off more clock cycles to execute each instruction. Nowadays, processors can execute more than one instruction per clock cycle. For example, today PCs have clock speeds up to GHz (Giga hertz, where Giga means billion and unit of cycle per second is hertz). Thus, one gigahertz is equal to one billion cycles or ticks per second. The speed of processor depends upon the clock speed. A processor can execute many instructions per second if clock speed is faster. Today, the speed of PCs is up to 3 GHz or more. So the speed of system clock is one of the factor that affects the performance of the computer. However, speed of the system clock has no effect on the input/output devices and storage devices.


Segment Registers

A block of memory is called a segment. The segment registers are used to store the addresses of the memory blocks that are being currently used by CPU Segment registers are also known as address registers. There are four segment registers named as CS, DS, ES and SS. Each has size of 2-bytes. These registers are used with IP register or with two index registers DI and SI to address various area or blocks of computer memory. A brief description of segment register is as


Base Register (BR)

Base register is used during arithmetic, logic and data movement operations. It stores memory addresses of data. It is also known as Index Register.


Counter Register (CR)

Counter register is used for counting purpose. It acts as counter for loops.


Data Register (DR)

Data register temporarily stores data (values) during arithmetic operation. The values are loaded into this register from memory through data bus. This register can only receive data from memory and cannot send data back to the memory.



Motherboard is the main circuit board of the system unit. It is also known as system board or main board. It is the most important circuit board inside the system unit. Many electronic components are connected to the motherboard and some components are built into it. The processor chip and memory chips are plugged (installed) into the motherboard. The motherboard contains sockets or slots in which electronic components are installed. You can say that motherboard is the master circuit board in a computer.

Arithmetic & Logic Unit (ALU)

Arithmetic & Logic Unit or simply ALU is another important component of CPU. It performs the arithmetic and logical operations on the data. When the control unit decodes an instruction related to perform arithmetic or logical operation on data, it sends instruction and data to the ALU.

* In arithmetic operations, ALU performs the addition, subtraction, multiplication and division.

* In logical operations, ALU compares the numerical data as well as alphabetic data. For example, it checks whether first number is greater than second, less than second or equal to second etc. Some of the logical operations can be done on text data. Similarly, to search a word in a document, the ALU matches each word of the document with the given word. Actually, the ALU compares each word of document with the given word.


CPU Socket

The CPU socket is the connector on the motherboard. The processor (CPU) is connected to a motherboard through this connector. CPU socket contains one or more small components that provide mechanical and electrical connections between CPU and motherboard. CPU sockets are mostly used on the motherboard in desktop and server computers.


Control Unit (CU)

The control unit is the most important component of the CPU. It controls and coordinates most of the operations in the computer. It acts as a central nervous system for the other components of the computer.

The Control unit Controls or directs different components of the computer by issuing control signals. For example, the control unit receives the data and instructions from the input device and stores them in the main memory. Similarly, i sends output to the output unit.

The control unit also controls the execution of instructions of the program. I fetches the instructions and data from the memory unit. It decodes and executes the instructions one by one. In case of arithmetic or logical operation, control unit issues command signal to arithmetic and logic unit (ALU). ALU performs the required operation on data. Control unit also provides clock pulses that are used to regulate and control all operations in the computer.




The system unit is main body o of the computer. It is a case that contains different electronic Components of the computer. These components include central processing unit, memory (i.e. disk drives, power supply, computer fan and other electronic components. All these components are connected to the motherboard inside the system unit. The case of the system unit is made of metal or plastic that protects the internal electronic components from damage. All computers and mobile devices have a system unit. The input/output devices and some storage devices such as USB flash drive are connected with the system unit. Different types of computers have system units of different shapes and sizes. In notebook or laptop computers, the keyboard and pointing device are built on the top of system unit. The display screen is attached to the system unit with hinges. In all-in-one desktop computer, both system unit and monitor are combined in a single device. Similarly, in mobile devices and many other mobile computers, display screen and keyboard are often built on the system unit. The examples of these mobile devices and mobile computers are smart phone, PDA, Ultra-Mobile PC, anti Tablet PC.



Central Processing Unit is simply called as CPU. It is the most important component of the computer. It is also known as processor. CPU is considered as the brain of the computer. It performs different operations on the data according to the given instructions. It also manages other operations of the computer.

CPU used in personal computer is known as microprocessor. It consists of a single chip. It is located on the motherboard inside the system unit. All other components of computer are connected to it through the Bus interconnection.

Today most of the processor chip manufacturers providing multi-core processors. A multi-core processor is a single chip that contains two or more separate processors. The most common multi-core processors are dual-core processors and quad-core processors. The dual-core processor chip contains two separate processors, while quad-core processor chip contains four separate processors. Multi-core processor typically increases the overall performance of the computer system.


Types of Processor Architecture

There are two types of processor’s architecture or design: CISC and Risc.

CISC Architecture

CISC stands for Complex Instruction Set Computer or Computing. CISC is a traditional architecture of CPU that supports a large number of complex instructions at the assembly language level. A single instruction can execute several low-level operations such as a load from memory, an arithmetic operation, and a memory store etc.

CISC architecture is complex because of the instructions used at the hardware level. CISC processors were developed by Intel. Today, these processors are mostly i used in personal computers. Examples of CISC processors are the Intel 486 series and Pentium series. AMD is another popular manufacturer of CISC processors.

RISC Architecture

RISC stands for Reduced Instruction Set Computer or Computing. It is considered new architecture of CPU that supports limited numbers of simple instructions. A single instruction can be executed within one clock cycle, so RISC processor executes simple instruction more quickly than CISC processor. Therefore, RISC processor is -Ty fast. RISC CPUs are used in workstations, mobile phones,


Parallel Processing

A method in which multiple processors are used simultaneously to execute a program is called parallel processing. In parallel processing, are divided among multiple processors. It means that program instructions run a multiple processors. Parallel processing makes a program run faster because there are multiples processors running it.

Today, some personal computers implement parallel processing with multi core processors. Supercomputers use parallel processing for complex applications such as artificial intelligence and weather forecasting. The parallel processing in supercomputers is usually known as massively parallel processing. It is a large scale parallel processing that involves thousands of processors.



An instruction consists of a group of bits that tells the computer to specific operation. The group of bits of an instruction is logically divided into different parts. Each part is used to perform a specific action. This Structure of instruction is called the instruction code format.

A computer has a variety of instruction code formats. The control unit is responsible to interpret the instruction code. The control unit also provides the necessary control function that needs the instruction to execute.

The instruction code format for a general-purpose computer consists of 16 bits. It has two parts:

1) Opcode (operation code) ii) Addresses of operands



The process by which CPU obtains a program instruction from memory decodes & executes it, and stores result in memory (if necessary), is called machine cycle. It is also known as instruction cycle. CPU performs the following bas operations to take action on each instruction of the program:



In fetch operation, the control unit obtains an instruction (or data item) from memory for taking action on it. The control unit performs the following steps to fetch an instruction:

* It gets the memory address of instruction to be executed from Program Counter (PC) register.

* It sends the memory address of instruction through address bus and read command through control bus for reading instruction.

* It places the instruction into the IR (instruction register) inside the processor (CPU).



In decode operation, the control unit (or instruction decoder which is a part of control unit) translates the instruction so that the computer can understand it. The control unit analyzes the op code of the instruction to determine the type of action to be performed. The control unit also reads any required data from main memory to be processed.



In execute operation, the control unit takes action on the decoded instruction, after decoding the instruction and getting the required data, the control unit execute. The instruction by using the activated circuits. The control unit generates control, signals needed to execute the instruction and sends these signals to the relevant unit that perform the actions required by the instruction. For example, control unit passes data and decoded instruction to ALU, which performs mathematical or logic operations on data according to instruction code.



CPU processes the data according to the instructions and stores result to the memory. The process of writing the result to the memory is called store.



A set of all instructions that a CPU can execute to perform different operations on data is known as the instruction set. Different types of CPUs have different instruction set. Usually, a modern CPU can execute 80 to 120 instructions.

Types of instructions

Generally, CPU provides the following types of instructions:

  • Data Transfer Instructions
  • Arithmetic & Logical Instructions
  • I/O Instructions
  • Control Transfer Instructions


Data Transfer Instructions

The instructions used to transfer data from one unit of computer to another during program execution are called Data Transfer Instructions, All CPUs provide different instructions for the transfer of data: data. These instructions can be used to transfer data:

* between main memory (RAM) and registers

* between registers and registers

* from input devices to main memory

* from main memory to output devices

Arithmetic and Logical Instructions

The instructions used to perform arithmetic operations on the data are called Arithmetic Instructions. The arithmetic operations may be addition, subtraction, multiplication or division. The arithmetic instructions are executed by the ALU.

The instructions used to perform logical operations on the data are called Logical instructions. Logical operation includes comparing two data values. Logical instructions are also executed by the ALU


I/O Instructions

The instructions used to write and read data to and from the h I/0 devices are called I/O Instructions. I/O devices are also known as peripheral devices. The peripheral devices may include keyboard, monitor, and disks etc.


Control Transfer Instructions

The instructions used to transfer the execution control from One part, program to another during program execution are called Control T; Instructions. These instructions may be used to execute or ignore a set of instructions after testing a condition. Similarly, these instructions may be used to execute a. instructions repeatedly for a specified number of times.


Parallel Processing

A method in which multiple processors are used simultaneously program is called parallel processing. In parallel processing, are divided among multiple processors. It means that program instructions run a multiple processors. Parallel processing makes a program run faster because there are multiples processors running it. Today, some personal computers implement parallel processing with multi core processors. Supercomputers use parallel processing for complex applications such as artificial intelligence and weather forecasting. The parallel processing in supercomputers is usually known as massively parallel processing. It is a large scale parallel processing that involves thousands of processors.



In some computers, the processor takes action (such as perform machine cycle) on only one instruction of program at a time. The processor waits until an instruction completes its all four steps or stages of machine cycle before beginning work on the next instruction.

Most of the modern computers support the concept called pipelining. In pipelining, the processor begins a new machine cycle before the current cycle is completed. The processors that use pipelining are faster because they do not have to wait for completing a machine cycle on an instruction. They can take actions on multiple instructions at the same time.



A component of the computer that is used to store data and instructions is called memory. Usually, it consists of one or more chips on the motherboard or some other circuit board in the computer. For example, personal computer contains a main memory. Before processing data, the control unit must load data and instructions in main memory.

Memory stores the following items:

  1. The operating system and other system software that control or maintain the computer and its devices.
  2. The application programs that are used to perform specific tasks. For example, to prepare a document, Microsoft Word program is loaded into memory.
  • Data to be processed by application program. After processing data, results are also stored in memory.

Storing data and programs in memory is known as stored program concept.


Memory Access Time

The amount of time required by a processor to read data or instruction from memory is called access time. Usually access time is measured in nanosecond (ns). A nanosecond is one billionth of a second. Some manufacturers state access time in megahertz (MHz). The access time affects the overall performance of the computer. The control unit can access any byte of data from the main memory by specifying its address. Different bytes from main memory can be accessed directly (or randomly). Accessing any part of the memory takes equal amount of time. It is very fast as compared to other storage devices such as hard disk and optical disk. For example, accessing data from main memory is more than 200,000 times faster than accessing data from hard disk. It is because; main memory does not involve any mechanical movement in accessing data or instruction.

Memory Size

The storage capacity of the memory is expressed in terms of number of bytes. The data and program sizes are also measured in bytes. Today, computer memories are available up to terabyte. In near future, memories will be available up to yotta bytes (YB). Following table shows the relationship between different memory measuring units:


Types of Memories

Computers or mobile devices contain two types of memories: volatile non-volatile.

Volatile Memory

A type of computer memory that requires continuous power (electricity) to maintain the stored information is called volatile memory. In this type of memory data and instructions are stored temporarily. It loses its contents (stored information) when computer is turned off. So it is a temporary memory. Examples of volatile memory are RAM, cache memory, and CPU registers.

Non-Volatile Memory

A type of computer memory that can maintain (retain) the stored information even when power supply is off (or interrupted) is called non-volatile memory. In this type of memory, data and instructions are stored permanently. It does not lose its contents when computer is turned off. So it is a permanent memory. Examples of nor-volatile memory are ROM, flash memory, CMOS, and all secondary storage devices.



RAM stands for Random Access Memory. It consists of memory Chips on the motherboard. It is used in a computer for the storage of active programs and data. The processor can directly write and read information (data & instructions) to and from RMVI. RAM is also called read/write memory; because processor can write and read information (data and instructions) to and from it. RAM is a primary memory, Data and instructions are stored in it temporarily.

The processor loads data and instructions in RAM from a storage device such as hard disk. The processor processes the data according to the program instructions by fetching the data and instructions from the RAM. The processor interprets and executes the program instructions while the program is in RAM. During this time, the contents of RAM may change. RAM can hold multiple programs simultaneously, provided the computer has enough RAM to accommodate all the programs. RAM is a volatile memory. It means that data and programs stored in RAM are lost when the power is turned off. The information must be saved on storage devices for later use. The storage capacity of RAM is measured in bytes. In PCs, the size of RAM is 4GB or more. More RAM size means the computer can use powerful program with large size. It also improves the data processing speed of the computer.



DRAM stands for Dynamic Random Access Memory. DRAM is the most common type of RAM used in the computers. In order to maintain information in DRAM chip, it must be refreshed with electric charge frequently (or periodically), otherwise data stored in DRAM will be lost. During refreshing process, CPU has to wait for writing and reading data to and from the DRAM. Therefore, it is slow memory.

Today many variations of DRAM chips exist and most of which are faster than the basic DRAM. The most important are SDRAM (Synchronous Dynamic RAM) and DDR SDRAM (Double Data Rate SDRAM).



It stands for Synchronous Dynamic Random Access SDRAM. SDRAM is an improved form of DRAM. It is much faster than DRAM. SDRAM actually synchronizes itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be read the CPU has not to wait for read write operation in the SDRAM.



DDR stands for Double Data Rate. DDR SDRAM is an advanced version of SDRAM and faster than SDRAM. DDR SDRAM is also called SDRAM II. DDR SDRAM has improved memory clock speed than SDRAM. It can read or write two consecutive words per clock cycle. New types of SDRAMs, known as DDR2, and DDR4 have also come which are used in latest microcomputers. DDR2 can read or write 4 words of data per clock cycle whereas DDR3 can read or write 8 data words per clock cycle. DDR SDRAM also Consumes less power, so it is ideal for notebook computers.



SRAM stands for Static Random Access Memory. It is faster and more reliable than DRAM. The SRAM chip does not have to be refreshed with electric charge frequently. So CPU does not have to wait to access data from SRAM. The SRAM chips utilize less power. The SRAM chip is more expensive than the DRAM chip. Static RAM is used as cache memory in computers.



MRAM stands for Magneto-resistive Random Access Memory. It store information using magnetic charges instead of electrical charges. It has great storage capacity and faster than other types of RAM (i.e. DRAM & SRAM). It also consumes less power. It is non-volatile memory because it does not lose its content (data & instructions) when computer is turned off. MRAM is also known magnetic RAM.



SIMM stands for Single In-line Memory Module. This circuit board (memory module) contains six to nine memory chips with pins that connect it to the motherboard. The storage capacity of memory chips mounted on the SIMM is from 256KB to about 32MB. SIMM has 32-bit bus (data path). SIMMs were used in early computers of 80s and 90s. Today, the SIMM is rarely used in computers because the processors of the modem computers (i.e. Pentium Microprocessor) require a 64-bit memory bus.



DIMM stands for Dual in-line Memory Module. A DIMM is a double SIMM. Like SIMM, this circuit board (memory module) also contains many memory chips with pins that connect it to the motherboard. The storage capacity of memory chips mounted on the DIMM is from 64MB to about 512MB. DIMM has 64-bit bus (data path). So DIMM is faster than SIMM because it enables to transfer more data at a time. SIMMs have been replaced by DIMMs. Nowadays, DIMMs are used in personal computers, workstations, and servers.



ROM stands for Read Only Memory. It is internal memory. The data and instructions stored in ROM can only be read. This is the reason why it is called read only memory. The data and instructions stored in ROM chip cannot be modified or deleted. However, in some types of ROM chips data and instructions and reprogrammed.

When the power is turned off ROM stores data and instructions permanently. The instructions stored in ROM are not lost. The ROM is, therefore, non-volatile memory.

The data and instructions are written into the ROM chip at the time of manufacturing. These ROM chips are called firmware. Mostly, frequently q y used small programs like operating system routines and data, are stored into the ROM. When the computer is switched on, instructions in the ROM are automatically activated, these instructions help the booting process of computer. System (BIOS). It performs the following functions during the booting usually, the set of instructions stored into ROM is called Basic Input computer.

* Checks different units of computer system.

* Loads the operating system into computer memory from disk etc.

Many other devices also contain ROM chips. For example, a printer has a ROM chip that contains data or information for fonts. You can say that each electronic device has ROM chip that contains information about say that each t that device.


Types of ROM

Different types of ROM are PROM, EPROM, and EEPROM.


PROM Stands for Programmable Read Only Memory. This type of ROM is initially blank. The user (programmer) can write data or programs on it according to his/her requirements using special devices. However, once the program or data is written in PROM chip, it cannot be modified. If there is an error in writing program or data in PROM, the error cannot be erased or removed. The PROM chip becomes unusable.


EPROM stands for Erasable Programmable Read Only Memory. This type of ROM is also initially blank. The user or programmer can write programs or data on it according to his/her requirements using special devices. Unlike PROM chip, the programs or data written in EPROM chip can be erased (removed) by using special devices and ultraviolet rays. So programs or data written in EPROM chip can be changed and new data can also be added. EPROMs are generally used in the devices in which information or programs are repeatedly changed (updated).


EEPROM stands for Electrically Erasable Programmable Read Only Memory. In this type of ROM, user can write or change instructions and information with the help of electrical devices. So data stored in this type of ROM chip can be modified easily.

This type of ROM works in a similar way as the flash memory. It is generally used to store a computer system’s BIOS and can be updated without removing from the circuit board. It is also non-volatile in nature.


Cache Memory

The processor obtains data and instructions from RAM during data processing. Often the processor obtains the same data or instructions from RAM again and again (or repeatedly). In this way, a lot of time of processor is wasted for obtaining same data or instructions from memory. So the performance of the processor is affected.

Cache memory is very small but very fast memory. It is used to improve the performance of processor (or computer system). Some cache memories are built inside the processor (CPU) and some are separate chips on the motherboard and are located between RAM and CPU. CPU stores frequently used instructions and data in cache memory. When CPU needs a specific data or program instruction, it quickly obtains from cache memory. So cache memory speeds up the working of CPU.

Types of cache memory

LI Cache

This type of cache memory is built into the processor chip. Its storage capacity is very small, ranging from 8 KB to 128 KB. But in modern PCs, its common size is 32 KB or 64 KB.

L2 Cache

This type of cache memory is also built into the processor chip but it Is slower than L 1 cache. However, its storage capacity is larger than Li cache. Its storage capacity is ranging from 64KB to 16MB.

Today, Advanced Transfer Cache (ATC) is used in processors. It is a type of L2 cache. It is also built into the processor chip. It is very fast memory. In PCs, its size is from 512 KB to 12 MB. In workstations and servers its size is from 12 MB to 16 MB.


L3 Cache

This type of cache memory is not built into the processor chip. It is located on motherboard between processor and RAM. It exists only in computer that use advanced transfer cache (ATC). In PCs, its size is up to 8MB and in servers and workstations, its size is from 8 MB to 24 MB.


Flash Memory

Flash memory is a type of non-volatile memory. It can be erased electronically and rewritten like EEPROM. Most computers use flash memory to store startup instructions. Flash memory chips are also used in mobile computers and peripherals devices to store data and programs. These mobile computers and devices include PDAs, smart phones, tablets, portable media player, printers, digital cameras, digital voice recorders, pagers etc. For example, when you enter names and addresses into a smart phones or PDA, a flash memory chip stores the data. Some portable media players store music on flash memory chip; others store music in memory cards. Memory cards contain flash memory on a removable device instead of a chip.


CMOS stands for Complementary Metal Oxide Semiconductor. It is similar to RAM but it is non-volatile memory. It is a high-speed memory. It uses battery to retain information even when the power to the computer is off. The contents of CMOS can be changed very easily.

CMOS is a special type of memory. It stores the configuration information about the computer such as information about type of disk drives, keyboard, monitor, system current date & time, password, system startup information etc.


A socket on the motherboard in which expansion card (or adapter Card) is inserted (plugged in), is called expansion slot. Different expansion slots are available on the motherboard to insert various expansion cards. For example, video display card, sound card, modem card, memory card and network card are inserted into expansion slots. The memory (RAM) card is inserted into the memory slot to expand the size of memory. Similarly, network interface card is inserted into expansion slot to connect the computer to a network and so on.

In modern computers, the circuitry of many of these cards is integrated in the motherboard to reduce size and cost.

Video Card

The monitor is connected to the system unit through the port (..,f video card. It enables a computer to display output (text, graphics and images) on the monitor screen. It converts computer output into a video signals. These signals travel through a cable to the monitor, which displays an image of output on the screen. A video card is also known as graphics card, display card, video adapter, video board, and video controller.

Sound Card

Sound card is used for input and output audio signals to and from tt computer. It is also known as audio card. The speaker, microphone and headphone are connected to the system unit through the ports of sound card. Sound card enables a computer to input and output sound. With the invention of sound cards in the 19Ks, we can store human voice in the computer through microphone and hear it through the speaker.


Network Interface Card (NIC)

It is commonly known as network card or LAN card. It is an expansion card that provides interface to a local area network (LAN). It enables a computer or device (that does not have built-in networking capability to access a network) to connect and communicate with other computers and devices in the computer network. It is installed in expansion slot on the motherboard. Each computer in the network must have a network card. Modern computers have integrated network interface circuit on the motherboard.

A network card follows the rules (or guidelines) of a particular communication standard, such as Ethernet or token ring. The most popular network interface card is Ethernet card. The data transmission rate of Ethernet card is from 10 Mbps to 100 Mbps.


A Point at which a device peripheral (such as keyboard, mouse, monitor, modem etc.) is connected to the Computer or mobile device is called port. The ports provide standard way of communication between the computer and its peripheral devices. A computer or mobile device has different types of ports to connect different peripheral devices. For example, in a desktop personal computer, the system unit contains different ports on its front and back.


Serial Port

A serial port provides a connection for transmitting data one bit at a time. Serial port is also known as communication (COM) port. The transmission of data through serial port is very slow. Its data transmission rate is 115 Kbps or more. The mouse, keyboard, and modem etc. are connected to the serial port. These devices do not require fast data transmission.

Serial ports were one of the earliest ports used in the computers. A serial connector is used to plug into a serial port. In old computers, serial ports were used with 9 or 25 pin connectors (male connectors), one pin for transmitting data while the other pins  for transmitting Control signals (for controlling the flow of data). In modern computers, serial ports have been replaced with USB ports.


Parallel Port

A parallel port provides a connection for transmitting data multiple bits at a time. The transmission of data through parallel port is faster than serial port. It is up to 12 Mbps or more. The printer and scanner are connected to the parallel port. Parallel ports are also known as Line Printer Ports (LPT).



A computer consists of different components and devices such as CPU main memory, I/0 devices etc. These components and devices are a set of parallel lines or wires. These are electrical paths or channels. A set of electrical paths/channels through which computer (CPU) sends and receives data and instructions (and also sends command signals) to and from different components of computer is called computer bus. The computer bus is backbone of the computer and computer cannot perform any function without it. Various devices or components of computer communicate with each other through buses. For example, buses are used to transfer data from input device to memory, from memory to output device or storage device or between memory and processor. The capacity of a bus depends upon the number of data lines it contains. The amount of data (or number of bits) that a Bus can carry at one time from one component of computer to another is known as bus width. For example, a bus ‘‘ith 32 lines can transfer 32 bits (or 4 bytes) at a time. Similarly, a bus with 64 lines can transfer 64 bits (or 8 bytes) at a time. The larger the number of bits handled by the bus, the faster the data transfer rate of computer.

The speed at which data transfers from one location to another inside the computer is called bus clock speed. Just like the processor, bus clock speed is measured in hertz. Today, bus clock speed is up to 1600 MHz or more (one Mega Hertz is equal to one million ticks per second). The higher the computer bus clock speed, the faster the transmission of data. It means that due to high computer bus clock speed, application running and data accessing speed will be very fast.

Types of Buses

A computer has two basic types of buses: System bus and Expansion bus.


System Bus

A system bus also called the front side bus (FSB). It is the part of motherboard. It connects the processor to main memory and other devices that reside on the motherboard. System Bus is divided into three types: Data Bus, Address Bus and Control Bus.


Data Bus

Data bus is used to transfer data (and instructions) between different components of computer. It connects the CPU, memory unit and other hardware devices on the motherboard. Data bus is bi-directional. It means that data can be sent and received through this electrical path. For example, CPU can vs rite and read data to and from the main memory through data bus.

Data bus consists of 8, 16, 32 or 64 parallel lines. A Data Bus of 64-line can transfer 64-bits (or 8 bytes) of data at a time. The number of lines in Data Bus affects the speed of data transfer between different components of computer.


Address Bus

Address bus is used to carry address information of different components or memory locations of the computer. Address bus is unidirectional. It means that information flows only in one direction. CPU can only send address information and cannot receive any information through address bus.

The components of computer are connected to one another through the address bus. Each component is assigned a unique ID. This ID is called the address of that component. When a computer component needs to communicate with another component, it uses address bus to specify the address of that component. Suppose CPU needs to read data from specific location of memory. It places the address of that memory location on the address bus. The address is carried to the memory. The data from the requested memory location is fetched and placed on the data bus.


Control Bus

A type of system bus through which CPU sends control signals to different components or devices of computer is called control bus. A control signal consists of the timing information and the command signal. The timing information specifies the time for which a device or component can use data bus and address bus. The command signal specifies the type of operation that is to be performed.

The CPU (control unit) controls the functioning of different components or devices of computer through control bus. These components and devices include input/output devices, main memory, secondary storage devices etc. The width of control bus is from 8 to 16 bits.

Suppose CPU wants to read data from the port attached to the keyboard. It will perform this activity as follow:

* sends out the address of keyboard port on the address bus.

* enables keyboard port by sending a signal on control bus.

* reads the data from the data bus. The data is put on data bus by the port.

Similarly, if CPU wants to read data from the main memory. It will use the control bus to send the “memory read” command to the main memory. The control bus is also used to transmit other control signals like ACKS (Acknowledgement signals). When CPU sends a command to the main memory for writing data, the memory sends back an acknowledgement signal to CPU after writing the data successfully.

Expansion Bus

The Computer buses that connect CPU (processor) to the peripheral devices are called expansion buses. The examples of peripheral devices are keyboard, mouse, modem, printer etc.

A peripheral device is connected to the system unit through a port on an adapter card or expansion card. The expansion card is inserted in an expansion slot on the motherboard. The expansion slot is connected to the expansion bus. The expansion bus is connected to the system bus. A processor communicates with the peripheral via expansion bus and system bus. Data transmitted to processor or memory travels from expansion slot through expansion bus and system bus. The width of expansion buses are typically from 16 to 64 bits.



ISA stands for Industry Standard Architecture. It is the most common and slowest expansion bus. It was developed for IBM personal computers. It is used to connect mouse, modem card, sound card, and low-speed network card. Its bus width is 8 or 16 bits.


PCI stands for Peripheral Component Interconnect. PCI is a high-speed expansion bus. It is about 20 times faster than ISA bus. It is used to connect high-speed devices. The video card, sound card, SCSI card, and high-speed network cards can be inserted in a PCI bus expansion slot. Its bus width is 32 or 64 bits. PCI bus was popular from 1995-2005. Today, in modern computers, PCI bus has been replaced with PCI Express bus or USB.


PCI Express (PCIe) Bus

The PCI Express (PCIe) bus is the latest expansion bus. Its data transfer rate is double than original PCI bus. It is used in microcomputers and laptop computers. Usually, it is used for the high speed graphics card and network interface card (NIC).


AGP stands for Accelerated Graphics Port. AGP bus is designed by Intel to improve the transmission speed of video and 3-D graphics. It provides faster, dedicated interface between the video card and memory.

USB & FireWire

USB and FireWire are buses that eliminate the need to install cards in expansion slots. In a computer with a USB/ FireWire, USB/ FireWire devices can be connected to the system unit through USB/FireWire ports.

PC Card Bus

PC Card Bus is used for PC card. Data travels on the PC card bus to the PCI bus.



Following are some important factors that affect processing speed computer. 1- Registers 2- RAM 3- System Clock 4- Computer Bus 5- Cache Memory


  • Registers

The small storage areas or locations inside the CPU are called registers. They store data and instructions during the execution of program. The size of registers is in bytes (which is from one byte to eight bytes). The large sizes of registers increase the performance of CPU. For example, a computer having 32-bit (4-bytes) registers means the CPU can process four bytes of data at a time. So the processing speed of computer is increased.

  • RAM

The RAM plays very important role in data processing. The program and the data must be loaded into RAM before running the program to process the data. The storage capacity of RAM or main memory is measured in bytes. More RAM means the computer can use powerful program with large size. The large RAM size also directly affects processing speed of the computer.

  • System Clock

System clock is an electronic component. It generates regular electronic pulses or ticks and controls all functions of the computer using these clock ticks. It is just like your heart that beats at a regular rate to keep your body functioning. It is because computer clock is known as heart of the computer. A processor can execute many instructions per second if clock speed is faster. Today, the speed of PCs is up to 3 GHz or more.

The pulses or ticks are also called cycles. The speed of microprocessors is measured by the number of cycles per second. If system clock generates more pulses, more instructions will be executed in one second. So system clock speed directly affects processing speed of the computer.

  • Computer Bus

A set of electrical paths through which computer (CPU) sends and receives data and instructions (and also sends command signals) to and from different components of computer is called computer bus.

The capacity of a computer bus depends upon the number of data lines it contains. For example, a bus with 32 lines can transfer 32 bits at a time. The amount of data (or number of bits) that a Bus can carry at one time from one component of computer to another is known as bus width. Bus width increasing the data accessing or processing speed of the computer.


AC Adapter

Some external peripheral devices such as an external modem, speakers etc. have an AC adapter. It is an external power supply which also converts AC power into DC power that the peripheral devices require. It is also used to recharge the battery in a mobile computer (such as laptop or tablet) or device. AC Adapter is also called AC converter or charger. One end of the AC adapter is plugged in the wall outlet and the other end is attached to the peripheral device.



Power supply is an electrical component which supplies power to the computer. It is installed inside the system unit and has its own cooling fan. It is a simple electrical system which converts the AC power into DC power. It takes 240 or 110 AC voltage and converts it into DC voltages of 3V, 6V, 12V and 24V. The low DC voltage is required to operate different components of a computer.



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