Computer Memory (RAM, ROM, PROM, EPROM, floppy disk, CD ROM, CD writer, DVD, Hard disk, pen drive)

The computer stores the data in an area known as memory. It can be compared to thousands of registers and files maintained in an office. The computer stores data in the forms of binary digits (0s and 1s) or Bits. The units are

• 8 Bits :1Byte
  1024 Bytes :1Kilo Byte (KB)
  1024 KB :1 Mega Byte (MB)
  1024 MB :1 Giga Byte (GB)
  1024 GB :1 Tera Byte (TB)

Memory can be classified into two types, namely

• Primary Memory
• Secondary Memory

PRIMARY MEMORY
Primary Memory or Main Memory is used to hold the program being executed and any other data currently in use. It is of two types namely:

Random Access Memory (RAM). Random access memory is Volatile Memory. It is also called Read/Write Memory. When the computer is switched off, information stored on the RAM is lost. Hence it is also known as Volatile Memory.

Read Only Memory (ROM). There are certain functions that the computer must perform when it is switched on. For example, connections have to be established within the various components if the computer and its peripherals. A series of programs are required to perform these functions. These programs are hardwired into the ROM Chips at the time of manufacture. ROM is non-volatile. When the computer is switched off, the data on these chips is not lost. Hence it is known as Non Volatile memory.

Programmable Read Only Memory (PROM). A variation of the ROM chip is PROM. PROM can be programmed to record information using a facility known as PROM Programmer. If the chip is programmed, the recorded information cannot be changed and PROM becomes ROM. This is also Non-volatile.

Erasable Programmable Read Only Memory (EPROM). Information in these chips can be erased by exposing them to ultra-violet rays. The chip can then be programmed afresh to record different information.


SECONDARY MEMORY

Secondary Memory or Auxiliary Memory is the area in which the processed data or information can be stored. The devices used are known as secondary storage devices.

Floppy Disk. It is a flexible plastic disk coated with a thin layer of Iron Oxide. They are available in three sizes viz. 31/2, 51/4 and 8 inches. The commonly used is the 31/2” floppy disk. The storage capacity of these disks is limited (1.44 MB).

CD ROM. CD ROM (Compact disk- Read Only Memory) has larger storage capacity. However to transfer information from your computer to the CD, you require a device known as a CD Writer. The CD can hold data amounting to 700 MB. A more advanced version is the DVD which can hold data anywhere between 1 GB and 16 GB.

Hard Disk. The Hard Disk is another storage device, which is fitted to the computer so that the processed data can be stored and accessed easily. The software required to run the computer and any additional software or programs are stored in the hard disk. The new version computers are equipped with 40, 80 or 160 Giga Bytes Hard disk.


Pen Drive. It is a small, dust proof, shock proof, very light weight storage device, used to transfer files between USB compatible systems conveniently. It is available in a range of capacities even up to 8 GB or more.

Input and output devices of a computer

The devices that help the user to communicate with the computer are input devices. Once the data is fed into the computer, it works on the data, processes it and provides the results to the user. The devices that help the user to get the output from the computer are output devices.

Input devices
Input devices are those devices that are used to feed data and programs into a computer.

• Keyboard: the keyboard of a computer resembles a typewriter with a few additional keys to handle various functions. A computer keyboard has three categories of keys:
  Alphanumeric keys: Alphabets, numbers, characters.
  Special keys: enter, backspace, Del, esc, Ctrl, alt.
  Function keys: (f1 to f 12) for selected operations.
• Mouse: the mouse is one of the most popular input devices. This device helps you to manipulate a pointer or an arrow on the screen. The pointer moves according to the movement of the mouse on a flat surface.
• Light pen: helps in identifying bar codes.
• Scanner: scans documents and photos and transmits them to the computer.
• Microphone: helps to record sounds to the computer and extensively used to talk through the internet.
• Web camera: Also called webcam is a small low resolution digital video camera. Web accessible cameras upload images to a web server.
• Joystick: used mainly to play games.

Output devices
These are the devices that are useful in receiving information or processed data from the computer. Some of the commonly used output devices are

• Visual display unit: the unit that resembles a TV screen and commonly referred to as ‘Monitor’. This unit informs us about the activities performed by the computer.
• Printers: printers are the primary output device used to prepare permanent documents. The printers that are widely used are Dot Matrix, LaserJet and Inkjet.
• Plotters: plotters are used for high quality diagrams. A pen is mounted on an arm, which moves along the paper with the help of motors. This is used in making high-resolution sketches and maps.
• Speakers: helps in listening to music and soundtracks of applications.

Input/output devices
The information in the disks is read by a disk drive. It is this same drive, which helps in writing or recording information to the disks (hard disk, floppy disk, CD R/RW). Hence, the disk drive is called an input/output device.