Computer : Memory


Computer memory is any physical device capable of storing information temporarily like RAM (random access memory), or permanently, like ROM (read-only memory). Memory devices utilize integrated circuits and are used by operating systems, software, and hardware.

Types of Memory

types of memory

Primary Memory

RAM (Random access memory) – Random Access Memory (RAM) is a type of data storage used in computers that is generally located on the motherboard. This type of memory is volatile and all information that was stored in RAM is lost when the computer is turned off

There are two types of Random access memory

  • Dynamic RAM – dynamic indicates that the memory must be constantly refreshed (reenergized) or it will lose its contents.
  • Static Memory – A computer memory that contains fixed information and retains its programmed state as long as the power is on.

Virtual memory is a feature of an operating system (OS) that allows a computer to compensate for shortages of physical memory by temporarily transferring pages of data from random access memory(RAM) to disk storage.

ROM (Read only memory) – Once data has been written onto a ROM chip, it cannot be removed and can only be read. Unlike main memory (RAM), ROM retains its contents even when the computer is turned off.ROM is referred to as being nonvolatile.

There are three types of Read only memory (ROM)

  • PROM – PROM stands for Programmable Read Only Memory. This form of ROM is initially blank. The user or manufacturer can write data/program on it by using special devices. However, once the program or data is written in PROM chip, it cannot be changed. If there is an error in writing instructions or data in PROM, the error cannot be erased. PROM chip becomes unusable.
  • EPROM – EPROM stands for Erasable Programmable Read Only Memory. This form of ROM is also initially blank. The user or manufacturer can write program or data on it by using special devices. Unlike PROM, the data written in EPROM chip can be erased by using special devices and ultraviolet rays. So program or data written in EPROM chip can be changed and new data can also be added. When EPROM is in use, its contents can only be read.
  • EEPROM – EEPROM stands for Electrically Erasable Programmable Read Only Memory. This kind of ROM can be written or changed with the help of electrical devices. So data stored in this type of ROM chip can be easily modified.


type of memory

A cache is a place to store something temporarily in a computing environment. Cache memory, also called CPU memory, is random access memory (RAM).

Memory units

Nibble<Bit < Byte < KB < MB < GB < TB < PB < XB < ZB < YB 

1 4 bit Nibble
2 8 bit 1 byte
3 1024 B 1 KB
4 1024 KB 1 MB
5 1024 MB 1 GB
6 1024 GB 1 TB
7 1024 TB 1 PB
8 1024 PB 1 XB
9 1024 XB 1 ZB
10 1024 ZB 1 YB

Secondary memory

Secondary memory – Secondary memory is a computer memory that is not directly accessed by the central processing unit (CPU) of a computer and is usually available as non-volatile memory. One of the most common forms of this memory is the hard drive of a computer, which is used to store the operating system (OS) and other programs. Example: DVD, CDs, Floppy Disk etc.

  • Hard Drive – a rigid non-removable magnetic disk with a large data storage capacity.
  • Floppy disk- A floppy disk, also called a diskette or just disk, is a type of disk storage composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. Floppy disks are read and written by a floppy disk drive (FDD).
  • Magnetic Tape – Magnetic tape used in recording sound, pictures, or computer data.
  • Flash memory – a kind of memory that retains data in the absence of a power supply.
  • Optical disk – an electronic data storage medium that can be written to and read using a low-powered laser beam.

CD-ROM: “Read Only” (used for distribution of commercial software, for example)Standard storage capacity is 640MB.

CD-R (or CD-WORM): “Write Once, Read Many” times

CD-RW: rewritable multiple times

DVD: similar to CD, but with significantly larger storage capacity (4.7GB)

Mother board – A motherboard is the main circuit board inside a computer that connects the different parts of a computer together. It has sockets for the CPU, RAM and expansion cards (e.g. discrete graphics cards, sound cards, network cards, storage cards etc)… and it also hooks up to hard drives, disc drives and front panel ports with cables and wires. Also Called as mainboard, system board.

Read More Computer Awareness Study Notes


Leave a Reply