Computer memory types and functions

Computer memory types and functions

Memory Unit of computer

Computer memory types and functions :  This unit is responsible to store programs or data on a temporary or permanent basis. It has primary memory (main memory) and secondary memory (auxiliary memory). The input data which is to be processed is brought into main memory before processing. The needed instruction for processing and any kind of intermediate results are also stored in primary memory. Together with these, the final output is also stored in primary memory before transferring it to the output unit. Another kind of memory is referred as secondary memory Poftar computer system. This unit is used to permanently store data,
programs and output. This unit does not deal directly with CPU.

Types Of Computer Memory:

In general the memory is classified into two categories as follows

  1. Primary memory or main memory .
  2. Secondary memory or auxiliary  memory.
  3. Cache memory.

Primary Memory

The memory unit that communicates directly with the CPU is called main memory or the internal memory the primary memory allows the computer to store data for immediate manipulation and to keep track of what is currently being processed . It is volatile in nature It Means that when the power is turned off the contents of the primary memory are lost forever.  Primary memory can be for the classified into two categories which are as follows:-

  • RAM (Random access memory).
  • ROM (Read only memory).

RAM (random access memory)

It is also known as read write memory that allows CPU to read as well as write data and instructions into it . RAM (random access Memory) is used for the temporary storage of input data ,output data and immediate results. There are of two categories of RAM are as follows :-

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

It is made up of memory cells where each cell is composed of one capacitor and one transistor. DRAM must be refreshed continually to store information . DRAM is slower less expensive and occupies less space on the computer’s motherboard.There are three types of DRAM :-

  • SDRAM .
  • RDRAM .
  • DDR -SDRAM .

DDR – SDRAM are of four types:- 

  • DDR 1 .
  • DDR 2 .
  • DDR 3 .
  • DDR 4 .
Static RAM (SRAM)

It retains the data as long as power is provided to the memory Chip . It needs not be refreshed periodically . SRAM uses multiple transistors for each memory cell. It does not use capacitor. SRAM is often used as cache memory due to its high speed. SRAM is more expensive than DRAM.

Advantages of RAM :-
  • It is volatile memory.
  • Fast data access.
  • It can read and write.
  • Stores dynamic data.
  • Improve computer performance.
  • Categorised by architecture and speed.
Disadvantages of RAM:-
  • Stores information temporarily.
  • Should match with compatible motherboards.

ROM (Read only memory):-

It is also known as non volatile memory or permanent storage. It does not lose its content when the power is switched off . ROM (read only memory )has only read capability , no right capability . ROM can have data and instructions written to it only one time. Once a ROM is programmed at the time of manufacturing it cannot be reprogrammed or rewritten. There are three categories of ROM as follows:-

  • Programmable ROM (PROM) .
  • Erasable programmable ROM (EPROM).
  • Electrically erasable programmable ROM( EEPROM).
Programmable ROM (PROM):-

It is also non volatile in nature. Once a PROM has been programmed its content can never be changed. It is one time programmable device. PROM’s are manufactured blank and can be programmed at buffer final test or in system. these types of memories are found in video game consoles, mobile phones, implantable medical device and high-definition multimedia interfaces.

Erasable programmable ROM (EPROM):-

It is similar to  PROM ,but it can be erased by exposure to strong ultraviolet light then rewritten .So it is also known as ultra violent erasable programmable ROM (UVEPROM).

Electrically erasable programmable ROM (EEPROM):-

It is similar to EPROM but it can be erased electrically then read it in electrically and the burning process is reversible by exposure to electric pulses. It is most flexible type of ROM and it is now commonly used for holding BIOS.


  1. Non-volatile memory 
  2. Data remains permanent inside ROM.
  3. ROM forms basics instruction set for operating the hardware .
  4. It can be updated 
  5. Stores programmed BIOS 


  1. If ROM is damaged, the computer system cannot function .


Basics for ComparisonRAMROM
Stands forRandom Access MemoryRead Only Memory
Memory TypeVolatileNon -Volatile
Memory Capacity1 to 256 GB per chip4 to 8 MB per chip
Operation TypeRead and Write bothOnly Read
SpeedFastComparitively slow
Storage TypeTemporaryPermanent
Also Referred as Primary MemorySecondary Memory
Presence of data according to power sourceThe Stored data in RAM lost in case of power failureData retained in ROM even if the power is turned off
Accessibility to processorProcessor can directly access the data in RAMprofessor cannot directly access the data in ROM
CostHighComparitively low

Secondary Memory 

These types of memories are internal or external storage devices are ideal inside or outside the computer. It store programs and data permanently you can assess any time when attached to the computer . You cannot store the data in primary memory permanently and primary memory cost higher than secondary. It is slower but cheaper. Floppy disk, hard drives ,CD ,DVD Pen drive etc are secondary storage devices. The secondary storage can be divided into magnetic device, optical device and flash memory.Some examples of secondary storage device are as follows:- 

  • Floppy disc
  • Hard disk drive 
  • Magnetic tape 
  • Compact disc 
  • Digital video disc (DVD)
  • Blu-ray disc
  • Pen/flash/thumb drive 

Floppy Disc (Diskette)

A Floppy Disk Drive (FDD) is a computer disk drive that enables a user to save data on removable diskettes. This portable storage device is a re-writable media and can be reused a number of times. It is made of plastic with magnetic coating on it. It is round in shape and is covered by square plastic jacket. Floppy disks are commonly used to move files between different computers. Although 8 disk drives made available in 1971 were the first real disk drives, the first widely used floppy disk drives were the 1/4″*5 floppy disk drives, which were later replaced with 3*1”/2 floppy disk drives. However, today these drives are being replaced with CD-R and other writable disc drives and flash drives. 5*1”/4 diameter-floppy has a capacity of 1.2MB. 3*1″/4 has a capacity of 1.44 MB.

Hard Disk Drive 

A hard disk drive (HDD) is a non volatile random access digital data storage device. It is a data storage device used for storing and retrieving digital information using rotating disc (platters) coated with magnetic material. All programs of a computer are installed in hard disk within a particular drive. A hard disk is a magnetic disk is made up of metal and covered with magnetic recording surface. Now a days there are use capacitive hard-disk available in the market to store the data like 500gb, 1TB, 30TB and even greater.

The hard disk has following components:-

  • Platter-The actual fix disk within the hard disk drive there can be several platters within the hard drive.
  • Heads- each side of a platter.
  • Tracks- large sections that completely circle the platter.
  • Sector- section on the track.
  • Cluster- Smallest unit of measurement that a hard drive will read.
  • Cylinder- tracks of the same diameter on each platter.

Magnetic Tape

It is a medium of data storage made up of a magnetic material. It is a storage medium on a large open reel or in a smaller cartridge or cassette (Like a music casset). It is used for those applications that are based on sequential  data processing example it is a sequential data access medium. Due to this (sequential data access) nature, these tapes are not suitable for data files that need to be revised or updated often . They are generally used to store backup data or that type of data which is not frequently used or to transfer data from one system to another.

Compact Disc (CD)

CD is the most popular and the least expensive type of optical disk. A CD Is capable of being used as a data storage device along with storing of digital audio . The files are stored on this particular contagious sector. CD’s are categorized into three main types as follows:-

  1. CD-ROM (Compact disk-read only memory).
  2. CD-R (compact disc- recordable).
  3. CD-RW (Compact disc -rewritable).

Characteristic of compact dick:-

  1. CDROM can store data up to 730 MB.
  2. Data stored can be zipped or unzipped.
  3. Compact in size.
  4. Permanent data storage.
  5. It is non volatile.


  1. It is cheaper.
  2. It is convenient to use.
  3. Compact in size.
  4. Can run in any CD drives.
  5. Supports read/ write format.

Digital video disk (DVD)

DVD is also known as super density disc (SDD) Aur digital versatile disc( DVD). A DVD is an optical disk storage media manufactured by Philips, Sony ,Toshiba and Panasonic in 1995 DVDs of a highest storage capacity than compact disk while having the same dimensions . Depending upon the Disk type DVD can store several gigabytes of data DVDs are primarily used to store music or six movies and can be played back on your television on computer to they are not rewritable media.DVDs come in three varieties as follows:-

  1. DVD ROM (digital video disc- read only memory).
  2. DVD-R (DVD-Recordable).
  3. DVD- RW(DVD- rewritable).

Characteristic of DVD:-

  1. It’s a digital disc.
  2. Compact in size.
  3. Store upto 45 GB .
  4. High reading speed.
  5. Work same as hard disk.


  1. High Data speed.
  2. Store large data.
  3. Good for storing multimedia files.
  4. Compact.
  5. Durable .
  6. High data security.
  7. Cheaper price.

Blu-ray Disk 

It is an optical disk storage medium design to recapture the data normally in DVD format. Bluray disk( BD) contains 25 GB per layers space.The name Blu-Ray Disk refers To the blue laser used to read the disc which allows information to be stored at a greater density e than the longer wavelength red laser used in DVDs. Blu Ray can hold almost five times more data than a single layer DVD. The variations in the formats are as follows:-

  1. BD-ROM(Read only)
  2. BD-R(Recordable)
  3. BD-RW(rewritable)
  4. BD-RE(rewritable)


  1. Large amount of data can be stored.
  2. Data stored is 10 times more than ordinary DVD.
  3. Convenient to record high resolution videos.
  4. Rewrite high-resolution videos.
  5. Not very expensive.

Pen/thumb Drive:-

Pen drive is also known as flash drive. A flash drive is a data storage device that consists of flash memory (key memory) With the portable USB interface. USB flash drives are typically removable, rewritable and much smaller than a floppy disc. Today flash drives are available in various storage capacities as to 256mb, 512MB, 1 GB, 4GB, 16GB up to 64 GB. They are widely used as an easy and small medium to transfer and store the information from their computer.


  1. Compact in size.
  2. Reliable.
  3. Cheaper in price.
  4. Convenient to carry.
  5. Whole data up to 32 GB.
  6. Lightweight.
  7. Used many times to read and write data.

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Pooja Rastogi

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