Computer Hardware

Basic components in a computer system are central processing unit (CPU), memory, the input device and output device.
System types
We can classify systems into the following categories:

  • 8-bit, example : 8085 microprocessor
  • 16-bit, example : 8086, 286, 386 processor
  • 32-bit , example : 486
  • 64-bit, example : Pentium – II

This gives us two basic system types or classes of hardware.

  1. 8-bit ( PC/XT) class systems
  2. 16/32/64 (AT) class systems

PC stands for personal computers, XT stands for eXTended PC, and AT stands for an advance technology PC. The XT basically was a PC system that included a hard disk for storage in addition to the floppy drive found in the basic PC system. These systems has an 8-bit processor and an 8-bit INDUSTRY STANDARD ARCHITECTURE (ISA) bus for system expansion. Bus is the name given to expansion slots in which additional plug in circuit board can be installed. 16-bit and greater systems are said to be AT class. 16-bit (and latter 32 and 64 bit) processors and expansion slots are included. The first AT class systems had a 16-bit version of the ISA bus which is an extension of the original 8-bit ISA bus found in the PC/XT class systems. Afterwards several expansion slots were developed for AT class systems.

  • 16/32 bit PS/2 microchannel architecture (MCA) bus.
  • 16-bit PC card (PCMCIA) bus
  • 16 bit ISA bus
  • 16/32 bit Extended ISA(EISA) bus
  • 32/64 – bit card Peripheral Component Interconnect (PCI) bus.

The easiest way to identify a PC/XT system is by the 8-bit ISA expansion slots regardless of the processor present in the system. AT systems can be similarly identified by having 16-bit of greater slots of any type (ISA, EISA, PCI) slots.


Motherboard is the important component of the computer as everything else is connected to it. And it controls everything in the system. Motherboard are available in several different shapes.Motherboard usually contain the following individual components.
1) Processor slot
2) Processor voltage regulators
3) Motherboard chipset
4) Level 2 cache
5) Memory SIMM or DIMM sockets
6) Bus slots
8) Clock / CMOS battery
9) Super I/O chips


The processor is often thought as the engine of the computer. Then the processor reads the commands from the memory and then executes them. the processor is one of the most expensive parts of the computers and is also one of the smallest parts.

The main component of any motherboard is the main processor chip which controls all the inner functions of the system. The CENTRAL PROCESSING UNIT(CPU) functions as the brain of every PC. It is usually inserted into the socket and is not soldered onto the motherboard as many other chips are normally done, this makes its replacement, in case of any problem, very easy. Some of the common CPU chips are:
8088,8086,80286,80386,80486, Pentium, Pentium MMX, Pentium–II, Pentium III, Pentium–IV, Intel i3 etc.


Memory is the place where computer stores the program(set of instructions telling ehe computer what to do), and data that help the program in carrying out its operations. For example, a marks sheet printing program will require students rollnumber, name and marks obtained in various subjects etc. as data. There is basically two type of memory used in a computer.

  1. RAM memory
  2. ROM memory

RAM memory:

RAM or random access memory is a read/write type of memory which is used by the processor to keep program, data and intermediate results during program executions. It is VOLATILE type of memory, which lose ists content when the power supply to it is switched off. The physical installation of RAM memory on the motherboard can take place in various ways.

  1. DIP(dual In-line Pin) memory chips were used on initial motherboards.
  2. Later SIMM ( single inline memory modules) became common.
  3. Currently DIMM(dual inline memory modules) are most common memory module.
  • Bit is a binary digit that is either 0 or 1.
  • Nibble is collection of 4 bits.
  • Byte is collection of 8 bits.
  • Kilobyte is 1024 bytes
  • Megabyte is 1024 Kilobytes
  • Gigabyte is 1024 Megabytes

Read Only Memory(ROM)

ROM or Read Only Memory, as its name suggest is a read only type of memory it cannot be written. Data is written into it by the manufacturer.

  • On major advantage with the ROM is, ROM is Non-Volatile type of memory i.e it does not lose its content when the power supply to it is switched off.
  • A motherboard normally contains one or more of these ROM chips.
  • The memory capacity of a ROM varies from one type of system to another.64 KiloByte (KB) was normally sufficient for a XT system, whereas as AT system requires 256KB of ROM.


BIOS is an abbreviation if Basic Input Output System. It is one of the most important program stored in the ROM. BIOS program lets your application program and the hardware such as floppy disk, hard disk, video adapter etc. communicate with each other.
The BIOS also contains a program called Power-On-Self-Test or POST. This post program checks the motherboard and other devices connected to the computer during the system power-on time. IBM made the original BIOS for their copyright product, but many compatible BIOS program BIOS program are available from Award, Phoenix, American Megatrends Inc. (AMI) etc. various manufacturers.

CMOS(Complementary Metal Oxide Semiconductor) Memory

In old IBM XT or compatible system, BIOS, with the help of jumpers, detected what all components are connected to the computer system.

  • IBM AT and higher systems do not contain these jumper switches and instead use a CMOS memory to store the system configuration, date, and time etc. information.
  • This CMOS memory receives power from a battery accompanying it, this battery helps it retains the information stored in it even when the system is switched off. When an AT or higher system is switched on, BIOS matches the information stored inside the CMOS with the components connected to the system and if it finds some mismatch or error, the BIOS displays some error message, explaining the problem.

There can be several programs in the system, which cannot be stored in RAM, so we need a very huge non-volatile memory, which can be used for storing all the programs, and data when the system is not in use are called as Hard disks.

CD-ROM drive

CD-ROM stands for compact disk read only memory. It consists of small disks similar to the gramophone records to hold digital information. As the name applies they are read only medium. With the advancement in technology writable CD’s are also available.

Floppy Disk Drive

Floppy disks are the slowest and the smallest form of secondary storage. They provide a simple way to carry information from one place to another, and backup small amount of files. In modern days floppy drive component is not as important as it was years ago. All PC’s made in the last 10 years use a standard 3 ½inch, 1.44 MB capacity floppy drive.


The keyboard is the main input device for most computers. It is used to input text or enter commands into the PC. Nowadays keyboards with additional features are available like multimedia keyboard, wireless keyboard.


With the invention of graphical user interface mouse is used to input information into the computer. Users simply point and click to enter information. The main advantage of mouse over keyboard is simplicity. And there are many operations that are much easier to perform with a mouse then a keyboard.


The monitor is the specialized high-resolution screen similar to a television. The video card sends the contents of its video memory to the monitor at a rate of 60 or more time per second. The actual display screen is made up or red, green and blue dots that are illuminated by electron beam from behind. The video card DAC chip controls the movement of the electron beam, which then controls what dots are turned on and how bright they are. Which then determines the picture you see on the screen.

Power supply

SMPS(Switch Mode Power Supply): The power supply supplies power to every single part in the PC. The main function of the power supply is to convert the 230 V AC into 3.3 V, 5 V and 12 V DC power that the system requires for the operations. In addition to supplying power to run the system, the power supply also ensures that the system does not run unless the power supplied is sufficient to operate the system properly. The power supply completes internal checks and tests before allowing the system to start. If the tests are successful, the power supply sends a special signal to the motherboard called Power_Good. If this signal is not present continuously, the computer does not run. Therefore, when the AC voltage dips and the power supply becomes stressed or overheated, the Power_Good signal goes down and forces a system reset or complete shutdown.

Peripheral Devices

Any external device, which is not necessary to perform the basic operation of computer, is called as peripherals. They provide additional computing capabilities. For example : Printers, Modems, Speakers etc.


Modem (Modulator and Demodulator) is typically used to send digital data over a phone line. The sending modem converts digital data into analog data, which can be transmitted over telephone lines, and the receiving modem converts the analog data back into digital form. This is used to connect to Internet. Modems are available in different capacities.

  • 300 bps – 1960s through 1983 or so
  • 1200 bps – Gained popularity in 1984 and 1985
  • 2400 bps
  • 9600 bps – First appeared in late 1990 and early 1991
  • 19.2 kilobits per second (Kbps)
  • 28.8 Kbps
  • 33.6 Kbps
  • 56 Kbps – Became the standard in 1998
  • ADSL, with theoretical maximum of up to 8 megabits per second (Mbps)


The capability to produce a printed version often called a hard copy of a document is the primary function of a printer. Different types of printers are 1) Laser 2) Inkjet 3) Dot-Matrix.