Computer Memory Unit | Computer Memory

Computer Memory Unit

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  • The Memory Unit is the part of the computer that holds data and instructions for processing.
  • Unit of computer system which stores the information on temporary or permanent basis is called memory. Mainly memory is of two types one is primary and the other is secondary.

computer memory unit

Primary Memory-

  • Primary Memory is used for immediate access of data by the processor.
  • Most computer systems around the world use primary memory.
  • Primary memory can be divided into two types.
    •  RAM (Random Access Memory)
    • ROM (Read Only Memory)

RAM (Random Access Memory)

  • Random Access Memory is the central storage unit in a computer system.
  • The information stored in the RAM is typically loaded from the computer’s hard disk, and includes data related to the operating system and certain applications.

There are primarily two forms of RAM

  • Static RAM (SRAM)
  • Dynamic RAM (DRAM)


  • Static RAM (SRAM)- This is most expensive among other forms of RAMs, but is generally faster and requires less power than DRAM and, in modern computers, is often used as cache memory for the CPU.
  • Dynamic RAM (DRAM) – Widely used in modern computers as primary memory, DRAM is slower than SRAM, but is inexpensive due to its one transistor-one capacitor paired assembly of memory storage.

Read Only Memory(ROM)

Read only memory is a chip in which information is stored by the manufacture. ROM chip is not volatile and cannot be changed by the user. Read only means cpu can read the data and program saved on  ROM chip, but cannot change the information or instruction given in computer ROM.

Types of ROM

  • PROM – Programmable Read Only Memory
  • EPROM – Erasable Programmable Read Only Memory
  • EEPROM – Electrically Erasable Programmable Read Only Memory


  • PROM Stands for “Programmable Read-Only Memory,” and is pronounced “p-rom,” not “prom“.
  • PROM is a type of ROM that is programmed after the memory is constructed.
  • While PROM cannot be erased, two other versions of PROM have been developed that can be erased and reprogrammed.


  • EPROM stands for Erasable Programmable Read-Only Memory.
  • This type of memory uses floating-gate transistors and can be erased by strong ultraviolet light.


  • EEPROM stands for Electrically Erasable Programmable Read-Only Memory.
  • EEPROM can be erased with an electrical charge and is used in flash memory.

Secondary Memory (Secondary Storage Device)

  • Secondary memory is used to storing the information in the computer system.
  • It may also refer to removable storage media, such as USB flash drives, CDs, and DVDs.
  • Secondary memory is much slower than primary memory, it typically offers a far greater storage capacity
  • Secondary memory includes Floppy disk,Hard disk drive,Optical disk,USB thumb drive


  • These are small removable disks that are plastic coated with magnetic recording material.
  • This portable storage device is a rewritable media and can be reused a number of times.

Computer Memory Unit

Hard Disk Drive

  • A hard disk consists of one or more rigid metal plates coated with a metal oxide material that allows data to be magnetically recorded on the surface of the platters.

Optical disk

  • An Optical disk is any storage media that hold content in digital format and is read using a laser assembly is considered as optical media.
  • The most common types of optical media are Blu-ray, CDs, and DVDs.
  • CDs can store up to 700 megabytes (MB) of data.
  • DVDs can store up to 8.5 GB of data.
  • Blu-ray discs, which are the newest type of optical media, can store up to 50 GB of data.

USB thumb drive

  • A USB flash drive is a data storage device that includes flash memory with an integrated Universal Serial Bus (USB) interface.
  • USB flash drives are typically removable and rewritable, physically much smaller than an optical disc.

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