Random
Access Memory
RAM (Random Access Memory) is the internal memory of the CPU for
storing data, program, and program result. It is a read/write memory which
stores data until the machine is working. As soon as the machine is switched
off, data is erased.
Access time in RAM is independent of the address, that is, each
storage location inside the memory is as easy to reach as other locations and
takes the same amount of time. Data in the RAM can be accessed randomly but it
is very expensive.
RAM is volatile, i.e. data stored in it is lost when we switch
off the computer or if there is a power failure. Hence, a backup
Uninterruptible Power System (UPS) is often used with computers. RAM is small,
both in terms of its physical size and in the amount of data it can hold.
RAM is of two types −
- Static RAM
(SRAM)
- Dynamic RAM
(DRAM)
Static RAM (SRAM)
The word static indicates that the memory retains its
contents as long as power is being supplied. However, data is lost when the
power gets down due to volatile nature. SRAM chips use a matrix of
6-transistors and no capacitors. Transistors do not require power to prevent
leakage, so SRAM need not be refreshed on a regular basis.
There is extra space in the matrix, hence SRAM uses more chips
than DRAM for the same amount of storage space, making the manufacturing costs
higher. SRAM is thus used as cache memory and has very fast access.
Characteristic of Static RAM
- Long life
- No need to
refresh
- Faster
- Used as cache
memory
- Large size
- Expensive
- High power
consumption
Dynamic RAM (DRAM)
DRAM, unlike SRAM, must be continually refreshed in
order to maintain the data. This is done by placing the memory on a refresh
circuit that rewrites the data several hundred times per second. DRAM is used
for most system memory as it is cheap and small. All DRAMs are made up of
memory cells, which are composed of one capacitor and one transistor.
Characteristics of Dynamic RAM
- Short data
lifetime
- Needs to be
refreshed continuously
- Slower as
compared to SRAM
- Used as RAM
- Smaller in
size
- Less expensive
- Less power
consumption
