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Computer Memory


Secondary Memory


Secondary Memory is also used to store data and information just like primary memory. These are used to provide back storage.

Since primary memory are expensive and amount of data that can be stored on it is limited so secondary memory is needed. 

 

More important points 

  • It is not as expensive as Primary memory
  • Its speed is slower than primary memory.
  • We can store programs and data into secondary memory that are not currently in use permanently and cn retrieve them later.
  • The secondary memory in micro-computers are provided by floppy disk and hard disks.

Method of accessing data from Secondary memory

The characteritics of memory can be determined by the order in which information can be retrieved or accessed from it.

There are four methods by which data and informations can be retrieved from the secondary memory.

  1. Sequential access
  2. Direct access
  3. Random access 
  4. Associative

Sequential access

As the name suggests, the data is searched in sequential manner from beginning address till the end untill the data is found.

So the data located at the last address would be found at the last since the search proceeds from beginning. Thus this technique is slow.

 

Example: Magnetic tapes, Magnetic disks, optical memories like CD-ROM

 

Random access

In random access any location of the memory can be accessed randomly.

 

Example: Semiconductor memories like RAM, ROM

 

Direct access

Direct access facilates direct access to the data or information.

This access technology can be considered as the combination of Sequential and Random access.

It allows to go directly to the location where data or information is stored. 

 

Example: Floppy disk, Hard Disk Drive (HDD), CD-ROM, DVD-ROM

 

Associative access

Associative access can be considered as a special type of random access method. 

It allows to make a comparison of required bit location within a word for a specific match.

Thus based on word's content, word is retrieved.

 

Example: Cache memory

 



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