Memory || Introduction Of Computer System || Bcis Notes


Computer memory is any physical device capable of storing the data or information for temporarily or permanently. In a computer system there are two types of memory they areas:

  • Primary memory(storage)
  • Secondary memory(storage)

Primary memory(storage)

  • This is the category of computer storage often called main memory.
  • It has three functions :
  • Stores all or part of the program that is being executed.
  • Stores the operating system programs that manage the operation of the computer.
  • Holds data that the program is using.

Modem primary storage devices include:

  • RAM
  • ROM

Random-access memory(RAM)


  • It is used for short term storage of data or program instructions.
  • It is volatile. Its contents will be lost when the computer’s electric supply is disrupted by a power outage or when the computer is turned off.
  • It is memory chips that can be read from and written to by processer.
  • The more RAM a computer has, the faster it responds.

There are two types of basic RAM chips:

  1. Dynamic RAM (DRAM)


  • It is the most common type.
  • It must be re-energized constantly
  1. Static RAM (SRAM)


  • It is faster and more reliable than DRAM.
  • It doesn’t have to be re-energized as often as DRAM.

Newer type: magnetoresistive RAM (MRAM).

Read-only memory(ROM)


  • It can only be read from; cannot be written too.
  • ROM chips come from the manufacturer with programs already burned in, or stored.
  • It is used in general-purpose computers to store important or frequently used programs such as computing routine for calculating the square roots of numbers.
  • It is a memory chip that stores permanent data and instructions.
  • It is a non-volatile memory, it is not lost when the computer power is turned off.

There are three types of RAM they are:

  1. Firmware: it is manufactured with permanently written data, instruction or information.
  2. PROMC(programmable read memory): chip onto which a programmer can write permanently.
  3. EEPROM(electrically erasable programmable read-only memory): it is a type of PROM containing microcode programmer can erase.

Secondary storage

  • It is used for relatively long term storage of data outside of the CPU.
  • Secondary storage is non-volatile and retains data even when the computer is turned off.
  • The most technologies are a magnetic disk, optical disk, and magnetic storage. Storage is the places of holding data, instructions, and information for further use. A storage medium is a physical material used for storage.
  • The storage medium is non-volatile contents are retained when power is off.
  • Memory is volatile it holds data and instructions temporarily.

There are various types of secondary memory or storage devices, they are a magnetic disk, optical disk, magnetic tape, etc.

A.Magnetic disk 

  • It permits direct access to individual records so that the datastore on the disk can be directly accessed regardlessly to the order in which the data were originally recorded.
  • Disk storage is often referred to as a direct access storage device (DASD).

There are two kinds of the magnetic disk:

1.Floopy disk

  • It is a portable, inexpensive storage medium which is also called distal. (thin, circular, flexible frim, enclosed in 3.5 wide plastic shell).
  • The device that reads from and writes to floppy disk is called floppy disk drive.

2.Hard disk


  • It is a high capacity storage system.
  • It consists of several inflexible, circular patterns that store items electronically.
  • Its components are enclosed in airtight, sealed case for protection.
  • The track is a narrow recording band that forms a full circle on disk.
  • Sectors stores up to 512 bytes of data.
  • Formatting prepares a disk for use and marks bad stores as unusable.

B.Optical disk

  • It is also called compact disks or laser optical disks as it uses laser technology to store data at densities many times greater than those of magnetic disks.
  • The most common optical disk system used with PCS is called CD-ROM(compact disk read-only memory)
  • It is a flat, round, portable metal discs made of metal plastic and lacquer.
  • It can be read-only or read and write.
  • In an optical disk, a tract is divided into evenly sized sectors that store items in them.

There are two types of an optical disk, they are:

1.CD-ROM(compact disk read-only memory)

  • Its contents cannot be erased or modified.
  • Typically it holds 650MB to 1GB data.
  • It is commonly used to distribute multimedia and complex software.

2.DVD-ROM(digital versatile disk-ROM or digital vide disk-ROM)

  • It stores database, music, complex software and movies.
  • Its contents can be erased or modified.
  • The high capacity disk is capable of storing 4.7GB to 17GB.
  • The computer must have a DVD-ROM drive or DVD player to read DVD ROM.

C.Magnetic tape

  • Magnetic tape is an older storage technology that is still used for secondary storage of a large volume of information.
  • The tape is magnetically coated plastic ribbon capable of storing large amounts of data at low costs. It is primarily used for backup.
  • Its advantages are its inexpensiveness, irrelative stability and ability to store very large quantities of information.
  • Its disadvantage is it sequentially stores data and its relative slowness compared to the speed of secondary storage media.


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