Computer Hardware & Software

Computer Hardware & Software

In this post we will tell you that What is the difference between computer hardware and computer software, and each topic will be in full detail. Computer hardware , all the parts of a computer that you can touch that called computer hardware, for example: CPU, RAM, Hard Disk, Power Supply, etc., and all the computer programs that you work on, but can’t touch them called computer software. For example: Windows, MS Word, Excel, Adobe Photoshop, Corel DRAW etc.
Now there are following tell you in detail about computer hardware & computer software.a

Computer Hardware

Basic Architecture of Computer System

Different computers have different architecture. However the basic organization remains the same for all computers systems. The Central Processing Unit (CPU) used in microcomputers is also called microprocessor. Main memory and CPU are mounted on a single board called the motherboard. There are basically three parts of a digital computer named CPU, Memory, and Input/ Output Devices.

CPU (Central Processing Unit)


CPU stand for central processing using. It is the brain of computer. It is also called processor. A computer cannot work without CPU. Each CPU has a set of pins through which all its communication takes place with the other devices. Some pins are used to carry the output signals from the CPU and others accept signals from the outside world. CPU consists of three units named ALU (Arithmetic and Logic Unit), CU (Control Unit), and MU (Memory Unit). CPU is located on the motherboard. 

1. Arithmetic and Logic Unit (ALU)

It is the part of CPU all types of data is processed. All arithmetic and logical operations are performed in arithmetic and logic unit. Arithmetic operations such as addition, subtraction, multiplication, division and logical operations such as less than, greater than and equality are performed in the ALU. Apart from the numeric data alphabetic data can also be compared according to an assigned sequence. When data is transferred using input devices to the primary storage, it will be there in primary storage until it is needed to the ALU where processing takes place. No processing occurs in primary storage. Intermediate results generated in the ALU are temporarily transferred back to the primary storage until needed at a later time. 

Data my thus move from primary storage to ALU and back again to storage any times before the processing is finished. Once complete, the final results are released to an output storage section and from there to an output device. The engineering design of ALU determines the type and number of operation that it can perform. 

To perform arithmetic and logic operations many hardware components are used like encoder, decoder, binary adder-subtractor, multiplexer, de-multiplexer, AND, OR, NOT gates etc. These components are combined to form ALU. Some of them are briefly described below:


It is circuit and used to convert one type of data into another. 


A decoder is a combinational circuit that converts binary information from n input lines to a maximum of 2n unique output lines.


Adder is used to add two numbers. The adder is part of the ALU, and some ALU contain multiple adders. in cases where two’s complement is being used to represent negative numbers it is trivial to modify an adder into an adder-subtractor.


A multiplexer or mux is a device that encodes information from two or more data sources into a single channel. They are used in situation where the cost of implementing separate channels for each data source is more expensive. 


A de-multiplexer is a circuit that receives information on a single line and transmits this information on one of 2n possible output lines. It has select lines as well. 


It is a circuit which gives output 1 if and only if all inputs are 1 otherwise it gives output 0. 


It is circuit which gives output 1 if and only if all inputs are 1 otherwise it gives output 0.


It is a circuit which converts 0 input to 1 and vice versa. 

Arithmetic Circuit

The basic component of arithmetic unit is adder. It is constructed with a number of full adder circuits. By controlling the data inputs to the parallel adder it is possible to obtain different types of arithmetic operations. 

Logic Unit

The logic micro operations manipulate the bits of the operands separately and treat each bit as a binary variable. Since all logic operations can be obtained by means of AND, OR, and NOT operations it may be more convenient to employ a logic circuit with just these operations.

2. Control Unit (CU)

It is an important component of CPU. It acts as a supervisor of the computer. By selecting , interpreting and seeing to the execution of program instructions the control unit of the CPU maintains order and directs the operation of the entire system. It provides the clock pulses that are used to control and manage the system. Although the control unit doesn’t process data, it acts as a central nervous system for the other data manipulating components of the computer. 

At the beginning of processing the first program instruction is selected and fed into the control unit from the program storage area. There it is interpreted, and then from there signals are sent to other components to execute the necessary action. Further program instructions are selected and executed one after another until the processing is complete. 

3. Memory Unit (MU)

CPU has its own memory to store data. Instructions are also stored in this memory. This memory area is called MU (Memory Unit) or CPU Registers. These are the fastest storage area in a computer. Few most commonly used registers of a CPU are AX, BX, CX, and DX. These registers are available in different sizes like 16, 32 and 64 bits. 


Memory can be classified into two types:

  • Random Access Memory (RAM)
  • Read Only Memory (ROM)

Random Access Memory (RAM)


Modern types of writable RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (Static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM). Some types have circuitry to detect and/or correct random faults called memory errors in the stored data, using parity bits or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask to permanently enable . disable selected transistors, instead of storing a charge in them. 

SRAM and DRAM are volatile, other forms of computer storage, such as disks and magnetic tapes, have been used as persistent storage in traditional computers. Many newer products instead rely on flash memory to maintain data when not in use, such as PDAs or small music players. Certain personal computers, such as many rugged computers and notebooks, have also replaced magnetic disks with flash drives. 

Similar to a microprocessor. a memory chip is an integrated circuit (IC) made of millions of transistors and capacitors. In the most common form of computer memory, dynamic random access memory (DRAM), a transistor and a capacitor are paired to create a memory cell, which represents a single bit of data. The capacitor holds the bit of information 0 or 1. The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state. 

Most of today’s computers use CMOS (Complementary Metal Oxide Semiconductor) technology for RAM. A state of the art CMOS memory chips about one eight the size of a postage stamp can store about 4,000,000 bits or more than 400,000 characters of data. Memory chips are installed on single inline memory modules or SIMMs. SIMMs are circuit board, which can hold a group of memory chips. 


The features of RAM are:

  • It is volatile 
  • It is costly 
  • It is temporary in nature 
  • It has unique addresses to store data.
  • It stores data in the form of 0’s and 1’s. 
  • It is available in larger size.
  • It is available in different sizes and speeds.
  • It is easier to replace in a computer.

Read Only Memory (ROM)

Pronounced ROM, acronym for read-only memory, computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read. 

Unlike main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile. Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs.  

Types of ROM

There are three types of ROM.


Data are written into a ROM at the time of manufacture. However, a programmable ROM (PROM) allows the data to be loaded by the user, by connecting a fuse between the emitter and the bit-line. PROMs provide flexible and economical storage for fixed programs and data, where high production volumes are involved. Initially, if the PROM contains all 1’s, then at the required location the user can insert 0’s, by burning out the fuses using high current pulses, this process is irreversible. However, the storage in ROMs will be very expensive when only a small number is required. Thus, PROMs provide a faster and less expensive approach for storing. 


The Erasable PROM chip allows the stored data to be erased and new data can be reprogrammed. It provides more flexibility during the development phase of digital system. With resemblance to the dynamic memory cell, information is stored in a capacitor is very well insulated and its rate of discharge is low. Hence it retains the stored information for more than a year. Due to high insulation, the process of writing new information into a cell involves the application of a higher voltage. The high voltage is used to cause a temporary breakdown in insulation and allow charge to be stored in the capacitor. the contents of EPROM cells can be erased by increasing the discharge rate of the storage capacitors. This can be accomplished by exposing the chip to ultraviolet light. All cells in the chip are erased at the same time. 


In an electrically erasable PROM, the contents of cells can be erased by the application of a high voltage. Advantages with EEPROMs are: it need not be physically removed for reprogramming and the process can be make selective since electrical erasure is used. 

EEPROM Features

The features of ROM are:

  • It is non-volatile 
  • It is cheaper than RAM 
  • It is static and will retain its contents.
  • It is more reliable than RAM as their circuit is simple
  • It is available in larger sized than RAM
  • It is not easy to replace in a computer

Computer Bus

A collection of wires through which data is transmitted form one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to internal bus. This is a bus that connects all the internal computer components to the CPU and main memory. There’s also an expansion bus that enables expansion boards to access the CPU and memory. 

The size of a bus, known as its width, is important because it determines how how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bit of data.

Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs the old ISA bus is being replaced by faster buses such as PCI. 

Nearly all PCs make today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor. Several different types of buses are used on Apple Macintosh computers. Older Macs use a bus called NuBus, but newer ones use PCI. 

There are three types of buses commonly used in computers. 

  • Data Bus
  • Address Bus 
  • Control Bus  

Data Bus

It is used to carry data signals, e.g. numbers which we want to add or the string which we want to compare. Data bus is also used to transfer data from main memory to CPU and then from CPU to any other output or storage device. 

Address Bus

It is used to carry address signals, e.g. address of a memory location or a port where an input or output device is attached. 

Control Bus

It is used to carry control signals. Control signal are used to control all the activities of the computers system.  Examples of control signals are read / write . enable / disable etc. 

Computer Software

Set of ordered instructions that enable a computer to carry out a specific task. A program is prepared by first formulating the task and then expressing it in an appropriate programming language. 

Following are the basic types of software:

  • System Software 
  • Application Software 
  • Utility Programs

System Software

System software, which consists of programs that control the operations of the computers and its devices, serves as the interface between user and the computer’s hardware. These programs do not solve specific problems. They are general programs written to assist humans in the use of the computer system by performing tasks such as controlling all operations required to move data into and out of a computer and all the steps in executing as application programs. Types of system software are the operating system and language processors etc. 

Operating System or Operating Software

An operating system is an integrated set of programs that is used to manage the various resources and overall operations of a computer system. It is designed to support the activities of a computer installation. Its prime objective is to improve the performance and efficiency of a computer system and increase facility and ease with which a system can be used. It also makes the computer system user friendly. 

Every general-purpose computer must have an operating to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such disk drives and printers. 

Operating systems can be classified as follows:

Multi User: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. 

Multiprocessing: Supports running a program on more than one CPU. 

Multitasking: Allows more than one program to run concurrently.

Multithreading: Allows different parts of a single program to run concurrently.

Real Time: Responds to input instantly. General purpose operating systems, such as DOS and UNIX , are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and and Windows, but others are available, such as Linux. 

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands some of them are given below.

Commands Usage
DIR This command is used to display the list of all the directories and sub-directories available.
CLS This command is used to clear the screen.
MD This commands is used to make a directory.
CD This command is Used to change the directory.
EDIT This command is used to invoke a text editor.
COPY We use COPY commands to copy some directory or file from one place to another place.
XCOPY We use XCOPY command to copy all the files of a folder from one place to another place.
DATE DATE command is used to display the current date.
TIME TIME command is used to display the current time.
VER VER command is used to display the version number of DOS.
RENAME RENAME command is used to rename a file or directory.

The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical User Interface (GUI) allow you to enter commands by pointing and clicking at objects that appear on the screen.

Languages Processors

These are the programs used to translate high level language program into low level language program. 


A program that translates code into object code. The 

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