Tuesday, April 17, 2012
RAM
The read and write memory (R/W) memory
of a computer is called RAM. The users can write information into RAM and read
information from it.
- It possesses random access property. In a random access memory any memory location can be accessed in a random manner without going through any other memory location. The access time is same for each memory location.
- RAM is a volatile memory. The information written into it is retained in it as long as the power supply is on. As soon as the power supply goes off its stored information is lost. The programmer has to reload his programs and data into the RAM when the power supply is resumed.
There are two types of RAM
Static RAM:
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It is also known as SRAM.
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Static RAMs retain stored information only as long as the power supply is
on.
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Static RAMs are costlier.
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It consumes more power.
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They do not need refreshing circuitry.
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They have higher speed than dynamic RAMs.
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Static RAM being faster is used in cache memory.
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Static RAM holds information in a flip-flop circuit consisting of two
cross-coupled inverters. Six transistors are needed per memory cell in a static
RAM.
Dynamic RAM
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It is also known as DRAM.
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Dynamic RAM loses its stored information in a very short time even though
the power supply is on.
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Dynamic RAMs have to be refreshed periodically, generally every 2
milliseconds.
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The dynamic RAMs are cheaper and have high packing density and moderate
speed.
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They consume less power.
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They are used where large capacity of memory is needed.
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Dynamic RAM being cheaper is used for main memory.
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Dynamic RAMs require less number of transistors per memory cell because
information is stored on stray capacitors. Only one transistor is needed to
form a memory cell of the dynamic RAM.
