Computer memory can be divided into three types: cache memory, primary/main memory, and secondary memory. Primary memory is directly accessible by the CPU and stores active data and instructions but loses data when powered off, consisting of RAM and ROM. RAM is read-write volatile memory for active data and programs while ROM is permanent read-only memory for firmware. Secondary memory is non-volatile storage like hard disks that the CPU accesses indirectly via primary memory and is used for permanent storage. Cache memory is very fast memory between the CPU and primary memory for frequently used data and instructions.

1. Computer Memory
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.

2. Types Of Memory
Basically there are three types of memory:-
• Cache Memory
• Primary Memory/Main Memory
• Secondary Memory

4. 1.Primary Or Main Memory
Primary memory holds only those data and
instructions on which the computer is currently
working and it is directly accessed by CPU. 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.

5. Types of Primary or Main
Memory
There are two types of memory:-
A-RAM(random access memory)
B-ROM(read only memory)

6. A.RAM
• 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. RAM is volatile, i.e. data stored in it is
lost when we switch off the computer or if
there is a power failure. There are two types of
RAM:-
• Static RAM (SRAM)
• Dynamic RAM (DRAM)

7. B.ROM
• ROM, which stands for read only memory, is a
memory device or storage medium that stores
information permanently. It is also the primary
memory unit of a computer along with the random
access memory (RAM). It is called read only
memory as we can only read the programs and
data stored on it but cannot write on it. It is
restricted to reading words that are permanently
stored within the unit.
• There are two types of ROM
1.PROM(programmable read only memory)
2.MROM(masked read only memory)

8. 2.Secondary Memory
• The secondary storage devices which are built into the
computer or connected to the computer are known as a
secondary memory of the computer. It is also known as
external memory or auxiliary storage.
• The secondary memory is accessed indirectly via
input/output operations. It is non-volatile, so permanently
stores the data even when the computer is turned off or
until this data is overwritten or deleted. The CPU can't
directly access the secondary memory. First, the secondary
memory data is transferred to primary memory then the
CPU can access it.
• Example:-Hard Disk, Pen Drive ,USB.

9. 3.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.