RAM
A
RAM constitutes the internal memory of the CPU for storing data, program and
program result. It is read/write memory. It is called random access memory
(RAM).
Since
access time in RAM is independent of the address to the word that is, each
storage location inside the memory is as easy to reach as other location &
takes the same amount of time. We can reach into the memory at random &
extremely fast but can also be quite 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 remains applied. 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 have to
be refreshed on a regular basis.
Because of the extra space in the
matrix, SRAM uses more chips than DRAM for the same amount of storage space,
thus making the manufacturing costs higher.
Static RAM is used as cache memory
needs to be very fast and small.
Characteristics of the Static RAM:
- It has long data lifetime
- There is 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 for it 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 because it is cheap and small. All DRAMs are
made up of memory cells. These cells are composed of one capacitor and one
transistor.
Characteristics of the Dynamic RAM:
- It has short data lifetime
- Need to refresh continuously
- Slower as compared to SRAM
- Used as RAM
- Lesser in size
- Less expensive
- Less power consumption
