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Computer Memory


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Computer Memory

The computer memory refers to the physical device which is used to store the programs or data. The data can be stored temporarily or on permanent basis. This data and programs can be used further for several purposes. Two main types of memory in a computer are:

  • Primary Memory: This memory is used to store data in the physical systems from where data can be accessed quickly. For example: RAM. The primary memory is easily accessible to CPU. The CPU continuously read and writes the data from primary memory. It is also known as main memory and internal memory.
  • Secondary Memory: This memory is not directly accessible to CPU. These are the physical storage devices which store all the programs and data of a computer. This memory also provides very large storing space for storing the data (as compared to primary memory). For example: hard disk.

When we talk about "Storage", it often refers to external storage device such as tape, floppy, optical disks and magnetic disks. But when we talk about "Memory", it often refers to internal memory of computers which is semiconductor memory in the form of integrated circuits and consisting of silicon transistors.

Semiconductor memory is of two types:

  • Volatile memory:

This memory requires continuous power supply to maintain the stored information. Till the power is ON, it will retain the data which is stored in it, but as the power is turned OFF, it will lose the data which is in it. It includes the primary memory of computer.

History Of Volatile Memory:

Volatile memory was in the form of following devices:

  • William Killburn Tubes: These tubes were used in 1946 and 1947 as primary memory in a computer. It consisted of cathode ray tube which stores the binary data electronically.
  • Delay Line Memory: It was used as primary memory in computers in 1947. It was refreshable memory.
  • Selectron Tubes: These tubes were used in computers as primary memory in 1953. These tubes works on the principle of William tubes, but these tubes were much more advanced as compared to william tubes.

Present Of Volatile Memory:

When concept of RAM came, it replaced all prior technologies. Following are some different types of RAM:

1. Static RAM: It stores current data, but do not lose it, till the power is on.

2. Dynamic RAM: It stores current data but it loses its data after a short time, even when power in on. It needs to be refreshed after a short interval.

There are also many other types of RAM. But i have focused mainly on two major types.

Future Of Volatile Memory:

Following are in development volatile memory devices:

T-RAM: It is combination of SRAM and TRAM. It provides high density as well as high speed.

Z-RAM: It is called Zero capacitor RAM. It uses the It uses the floating body effect.

TT-RAM: It is known as Twin Transistor RAM. It uses two transistors instead of one transistor and one capacitor (as used in DRAM).

  • Non-Volatile Memory:

This memory does not require continuous power supply to maintain the stores information. The data once stored in it, will remain safe even if the power is turned OFF.

History Of Non-volatile Memory:

Following are the devices that had been used as non-volatile memory in past.

  • Drum Memory: It was a magnetic data storage device that was used from 1932 till 1950's.
  • Magnetic Core Memory: It used magnetic rings as core to store the data.
  • Plated Wire Memory: It was a modified form of magnetic core memory.
  • Twisted Memory: It was also a modified form of core memory.
  • Bubble Memory: It uses a thin film of magnetic material to store the data.

Present Of Non-volatile Memory:

Following are some of hardware that are being used as non-volatile memory in current era.

ROM(Read Only Memory):

It is a memory in a computer which can be read but (unlikely RAM) it is very difficult to write. It has following types:

  • Mask ROM: In this ROM, contents of the memory are programmed by integrated circuit manufacturer.
  • P-ROM: This ROM can be programmed after its construction.
  • EP-ROM: The data in this ROM, can be erased and re-programmed.
  • EEP-ROM: It can be modified by the user.

NV-RAM:

It is the RAM which is able of retaining its data even if the power is turned OFF.

Future Of Non-volatile Memory:

Following are the hardware of non-volatile memory which are in development.

CB-RAM:

It is also known as programmable metallization cell (PMC). It works on the principle of relocation of ions in an electrolyte.

SONOS:

It is Silicon oxide-Nitride oxide-Silicon. It is similar as flash memory but it uses the silicon nitride instead of poly-silicon for storing the data.

R-RAM:

It is known as resistive random access memory. It is a combination of CB-RAM and Phase change memory.

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