A
memory is just like a human brain. It is used to store data and instructions.
Computer memory is the storage space in the computer, where data is to be
processed and instructions required for processing are stored. The memory is
divided into large number of small parts called cells. Each location or cell
has a unique address, which varies from zero to memory size minus one. For
example, if the computer has 64k words, then this memory unit has 64 * 1024 =
65536 memory locations. The address of these locations varies from 0 to 65535.
Memory is primarily of three types −
- Cache Memory
- Primary
Memory/Main Memory
- Secondary
Memory
Cache Memory
Cache memory is a very high speed semiconductor memory which can
speed up the CPU. It acts as a buffer between the CPU and the main memory. It
is used to hold those parts of data and program which are most frequently used
by the CPU. The parts of data and programs are transferred from the disk to
cache memory by the operating system, from where the CPU can access them.
Advantages
The advantages of cache memory are as follows −
- Cache memory
is faster than main memory.
- It consumes
less access time as compared to main memory.
- It stores the
program that can be executed within a short period of time.
- It stores data
for temporary use.
Disadvantages
The disadvantages of cache memory are as follows −
- Cache memory
has limited capacity.
- It is very
expensive.
Primary Memory (Main
Memory)
Primary memory holds only those data and instructions on which
the computer is currently working. It has a limited capacity and data is lost
when power is switched off. It is generally made up of semiconductor device.
These memories are not as fast as registers. The data and instruction required
to be processed resides in the main memory. It is divided into two
subcategories RAM and ROM.
Characteristics of Main Memory
- These are
semiconductor memories.
- It is known as
the main memory.
- Usually
volatile memory.
- Data is lost
in case power is switched off.
- It is the
working memory of the computer.
- Faster than
secondary memories.
- A computer
cannot run without the primary memory.
Secondary Memory
This type of memory is also known as external memory or
non-volatile. It is slower than the main memory. These are used for storing
data/information permanently. CPU directly does not access these memories,
instead they are accessed via input-output routines. The contents of secondary
memories are first transferred to the main memory, and then the CPU can access
it. For example, disk, CD-ROM, DVD, etc.
Characteristics of Secondary Memory
- These are
magnetic and optical memories.
- It is known as
the backup memory.
- It is a
non-volatile memory.
- Data is
permanently stored even if power is switched off.
- It is used for
storage of data in a computer.
- Computer may
run without the secondary memory.
- Slower than
primary memories.
