Computer Peripheral Devices and Their Functions Explained

This tutorial explains computer peripheral devices and their function in details with examples. Learn how computer peripheral devices (such as RAM, ROM, processor, input and out device, motherboard and storage device) work with functions and specifications.

Bits & Bytes

Computers are devices powered by electricity, which has two discrete states: On or Off.

  • To be processed, all data in a computer system (words, symbols, pictures, videos, sounds) must be reduced to a string of binary digits.
  • A binary digit 1 or 0 is called a bit,
  • Eight bits grouped together as a unit are called a byte, which provides enough combinations of 0s and 1s to represent 256 individual characters, including numbers, upper and lower case alphabet letters, punctuation marks and other characters
Name Abb Approx. Bytes Exact Bytes Approx. Pages of Text
Byte B One 1 One character
Kilobyte KB (or K) One thousand 1,024 One-half page
Megabyte MB One million 1,048,576 500 pages
Gigabyte GB One billion 1,073,741,824 500,000 pages
Terabyte TB One trillion 1,099,511,627,776 500,000,000 pages
Coding Schemes

Define the patterns of bytes

Coding schemes, such as ASCII, EBCDIC, and Unicode, provide the means to interact with a computer

When a letter is pressed on a keyboard, the electronic signals are converted into binary form and stored into memory.

The computer processes the data as bytes of information and converts them to the letters we see on the monitor screen or on a printed page.

computer coding

The System Unit

The System Unit houses the central processing unit, memory modules, expansion slots, and electronic circuitry as well as expansion cards that are all attached to the motherboard; along with disk drives, a fan or fans to keep it cool, and the power supply.

All other devices (monitor, keyboard, mouse, etc., are linked either directly or indirectly into the system unit.

Front of the System Unit

Drives are housed in drive bays which are accessed at the front of the case.

Internal drives, such as the hard disk drive, are installed in internal bays that are not typically as accessible as the external drives pictured here.

front pannel

System Unit cases come in a huge array of types and styles, depending upon hardware needs.

Types of Ports

serial port

Serial ports

transmit data one bit at a time, like the picture on the left illustrates.

Parallel ports

transmit more than one byte at a time.

These types of port designs are based on whether or not fast data transmission rates are required by the device or not.

Most computers come with basic types of ports (serial, parallel, keyboard, mouse, and USB); and expansion cards allow you to expand the available types needed by specific devices.

Different Types of Connectors


Understanding the differences among connector types is useful and important, as the cable required to attach a device to your computer is specific to its connector, not to mention the port on the computer.

Non-Volatile Storage Devices

Disk drives

  • Internal & External
  • Hard drives
  • Removable disk drives
  • Floppy disks (1.4 MB)
  • ZIP disks (100/250 MB)
  • CD-ROM (700MB), DVD-ROM (~5GB/side)
  • read only (-ROM), write once (-R), re-writeable (-RW)
  • Combination drive

Many other forms
Memory Stick, MultiMediaCard, CompactFlash, and SmartMedia

Hardware components

Input devices -

accept data or commands in a form useable by computers

Output devices

display the processed information - printers, monitors, speakers.

Processing devices

in system unit and are comprised of circuitry.

Storage devices -

Drives read from and write to storage media (the physical material that can store data and programs).

Communication devices

provide connections between computers and communication networks, allowing for exchange of information and data with other computers via transmission media such as cables, telephone lines, and satellites


Input Devices
  • Keyboards
  • Pointing Devices mouse, trackballs, joysticks, touchpads and light pens
  • Source Entry devices Scanners, Audio input devices, video input devices, digital cameras
Output Devices

Monitor /Display Screens CRT and Flat Panel (LCD), EL and gas plasma

Monitor /Display Screen clarity

refers to the number of dots displayed in the X (across) and Y (down) co-ordinates.
expressed in terms of horizontal pixels X vertical pixels.
Typical screens are capable of displaying 640x480 dots

Dot Pitch
measurement of how close together the pixels, or phosphor dots, are that make up an image.
The smaller the dot pitch, the crisper the image,0.31 or less provides a sharp image, especially when displaying text.

Refresh rate
the vertical frequency, or the rate at which each pixel on a screen is re-drawn. A low refresh rate results in an image that flickers, resulting in eye-strain.
A refresh rate of 60Hz means the images is redrawn 60 times a second. Typical refresh rates are 60Hz, 72Hz and 75Hz.

Video Display Adapters

Display graphics - Visual output from your system.
Works between the system's processor and monitor
Relays the information received from the programs and applications running on the system to the monitor

VDAs come with their own memory chips (RAM or VRAM for video RAM) which determines how fast the card processes images, the resolution, and how many colours it can display.
VDA embody certain standards.
Todays PCs commonly use VGA and SVGA standards

Hardcopy Output : Printers
Impact Printers

The general features of impact printers are uses force by applying hammer pins to strike the paper

  • slow speed
  • prints on most paper types
  • transparencies not supported
  • multiple copies may be printed at once

Advantages : Less expensive, Fast (some types) , Can make multiple copies with multipart paper

Disadvantages : Noisy! Print quality lower in some types. Poor graphics or none at all.

Dot-Matrix and Daisy-Wheel.

Dot matrix printers form characters using row(s) of pins, 9, 18, or 24 which impact the ribbon on top of the paper.

Daisy wheel printers use a spoked wheel with characters placed at the end of each spoke. A print hammer is used to strike the desired character onto the ink ribbon and then the paper.

Hardcopy Output : Printers
Non Impact Printers

General features print head does not make contact with the paper

  • higher speed in characters per second is possible
  • prints on most paper types but better quality obtained with better paper
  • transparencies usually supported
  • Uses ink spray or toner powder
  • Offer superior quality and greater options (in terms of the number of fonts and quality of graphic pictures)

Disadvantages : more expensive.

The three main types of non-impact printers are laserjet, inkjet and thermal

Characters of printers

Speed: The speed of a printer is measured in: cps= characters per second, lpm= lines per minute ppm= pages per minute The faster the printing, the more expensive the printer.

Resolution: A more numerical measure of print quality is printer resolution. Measured in dots per inch (dpi), this determines how smooth a diagonal line the printer can produce.

Cable connection:

Serial Cables- send data only 1 bit at a time- Distance from PC 1000 ft

Parallel Cables- send data 8 bits at a time. Distance from PC 50 ft.- Most popular - USB cable which has a maximum data transfer speed of 12 megabits/s (1.5 MBYTES/s).

The Motherboard

The motherboard is the main circuit board of a computer. It contains the central processing unit (CPU), the Basic Input/Output System (BIOS), memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers for standard peripheral devices like the keyboard, disk drive and display screen.

The chipset and other motherboard circuitry are the "smarts" of the motherboard. Their job is to direct traffic and control the flow of information inside the computer.

The chipset is a critical part of any computer, because it plays a big role in determining what sorts of features the computer can support.


  • BIOS stands for Basic Input/Output System.
  • lowest-level software in the computer
  • Acts as an interface between the hardware (especially the chipset and processor) and the operating system.
  • The BIOS provides access to the system hardware and enables the creation of the higher-level operating systems that you use to run your applications.
  • The BIOS is also responsible for allowing you to control your computer's hardware settings, for booting up the machine when you turn on the power or hit the reset button, and various other system functions.
ROM: Read Only Memory
  • ROM is nonvolatile. ROM chips contain permanently written data, called firmware (your BIOS lives here).
  • ROM contains the programs that direct the computer to load the operating system and related files when the computer is powered on.
  • ROM chips are usually recorded when they are manufactured.

PROM -Programmable Read Only memory chip cannot be changed to update or revise the program inside

EPROM Erasable Programmable Read Only memory Data can be erased and chip can be reused Can be erased by shining high intensity UV light through the window

EEPROM Electrical Erasable Programmable Read Only memory under high voltage

FROM -Flash ROM is reprogrammable memory using normal voltage inside the PC- You can upgrade the logic capabilities by simply downloading new software. This saves the expense of replacing circuit boards and chips.

Processing Devices

Processing Devices


Pronounced cash.

It is a small, high-speed memory area that is placed between the processor and the system memory.

The value of the cache is that it is much faster than normal system memory.

The most frequently used instructions are kept in cache memory so that the CPU can look in there first - allows the CPU to run faster because it doesn't have to take time to swap instructions in and out of main memory.

Large, complex programs such as complex spreadsheets or database management programs benefit the most from having a cache memory available. Pentium II processors generally come with at least 512 KB of cache memory.

Random Access Memory (RAM)
  • RAM is Primary Storage, also called internal storage.
  • Serves as computers workspace, storing all or part of the program that is being executed, as well as data being used by the program.
  • RAM provides instructions and data to the CPU.
  • These instructions/data are coded in bytes.
  • Each byte is placed in a precise location in memory, called an address.
  • To access data or instructions in memory, the computer references the addresses containing the bytes.
  • The amount of memory available is therefore measured in bytes


  • RAM chips consist of millions of switches that are sensitive to changes in electric current.
  • RAM chips are typically packaged on small circuit boards called memory modules, which are inserted into special slots on the motherboard.
  • RAM is Volatile storage: Power goes, data goes!
  • Data/instructions are copied into memory as needed.
  • Not enough memory or corruption of data/instructions in memory can cause crash.
  • On booting, operating system files are loaded from a storage device (the hard disk, usually) into RAM, and they remain there as long as your computer is running.
  • RAM contents changes as programs are executed.
  • RAM chips consist of millions of switches that are sensitive to changes in electric current.
  • RAM chips are typically packaged on small circuit boards called memory modules, which are inserted into special slots on the motherboard.
  • On booting, operating system files are loaded from a storage device (the hard disk, usually) into RAM, and they remain there as long as your computer is running.
  • RAM contents changes as programs are executed.
  • The amount of RAM needed depends on the types of applications you intend to run on the computer. S/w indicate the minimum amount of RAM required to run.

Two basic types of RAM are Dynamic RAM (DRAM), and Static RAM (SRAM).

Most computers today use DRAM, which are also of two types:

  • SDRAM Synchronous Dynamic RAM runs at the same pace as the system clock runs
  • DDR SDRAM DDR stands for Double Data Rate - runs at double the pace the system clock runs - available in speeds from 266 MHZ upto 600MHZ
  • DDR2 SDRAM runs at four times the pace the system clock runs - available in speeds from 400 MHZ upto 800MHZ

Most desktops and notebooks use one of the three most popular types of synchronous dynamic random access memory (SDRAM) for the main system memory. Single data rate (SDR) SDRAM is the older type of memory, commonly used in computers prior to 2002. Double data rate (DDR) SDRAM hit the mainstream computer market around 2002, and DDR2-based systems hit the market in mid-2004.

DDR SDRAM is a straightforward evolution from SDR SDRAM. The big difference between DDR SDRAM and SDR SDRAM is that DDR reads data on both the rising and falling edges of the clock signal, so the DDR module can transfer data twice as fast as SDR SDRAM.

While DDR has a limited clock rate, the evolutionary changes to DDR architecture enable DDR2 to achieve speeds beyond of DDR, delivering bandwidth of 5.3 GB per second and beyond! Because DDR2 is able to operate with faster bus speeds, your memory doesn't hold back the performance of your processor.

Generally speaking, motherboards are built to support only one type of memory. You cannot mix and match SDRAM, DDR, or DDR2 memory on the same motherboard in any system. They will not function and will not even fit in the same.

Why is RAM so important?

Aside from the processor, the two most important factors affecting a PC's performance are RAM and hard disk capacity.

Hard disks are typically huge, so the primary limiting factor is the amount of installed RAM.

Without enough RAM, the operating system must swap out storage space with the hard disk. The OS creates a Paging File (swap file) to supplement RAM (workspace). This is Virtual Memory.

Virtual memory is inherently slow! RAM speed can typically be 120,000 times FASTER than the hard disk so the less you must rely on virtual memory (swapping files between RAM and hard disk), the faster your system will perform.

  • Heart and brain of the PC
  • One electrical circuit in control of another
  • Successive generation of processors
  • 80286,80386,80486 -32 bit interface
  • Pentium family P1, P2, P3, P4 64 bit interface
  • Dual-core technology is like having two processors - A dual core processor is a CPU with two separate cores residing on the same chip
  • Hardware (H/w) All machinery & Equipments Computer & Peripherals
  • Peripherals Any piece of hardware connected to the PC
  • Software (S/w) programs- tells the Computer how to perform a task
    • Systems Software (S/w) For managing internal activities & run applications s/w Interpreter bet S/w & H/w
    • Application Software (S/w) - to perform a specific task Custom or Packaged

ComputerNetworkingNotes Networking Tutorials Computer Peripheral Devices and Their Functions Explained