Primary memory (RAM and ROM) is the working memory of a computer that holds the data and instructions currently being processed. It is volatile and has limited capacity. Secondary memory (HDD, DVD, etc.) is used for permanent storage of large amounts of data and retains data even when powered off. RAM is faster than ROM but volatile, while ROM is non-volatile but slower and used for startup processes. Primary memory is accessed directly by the CPU while secondary memory requires data to be copied to primary memory first before CPU can access it.

1. Types of Memories
Presented By :- Mrs. Surkhab Shelly

2.  Memory unit is the amount of data that can be stored in the
storage unit. This storage capacity is expressed in terms of
Bytes.

3. COMPUTER
MEMORY
PRIMARY
MEMORY
RAM
ROM(NON-
VOLATILE)
SECONDARY
MEMORY
HDD
FLOPPY
DISK
MAGNETIC
DISK
PENDRIVE

4. 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.

5. Random Access Memory (RAM) –
• It is also called as read write memory or the main memory or the primary
memory.
• The programs and data that the CPU requires during execution of a program
are stored in this memory.
• It is a volatile memory as the data loses when the power is turned off.
• RAM is further classified into two types- SRAM (Static Random Access
Memory) and DRAM (Dynamic Random Access Memory).

6. Read Only Memory (ROM) –
 ROM Stores crucial information essential to operate the system, like the program
essential to boot the computer.
 It is not volatile.
 Always retains its data.
 Used in embedded systems or where the programming needs no change.
 Used in calculators and peripheral devices.
ROM is further classified into 4 types- ROM, PROM, EPROM, and EEPROM.
 Types of Read Only Memory (ROM) –
 PROM (Programmable read-only memory) – It can be programmed by user. Once
programmed, the data and instructions in it cannot be changed.
 EPROM (Erasable Programmable read only memory) – It can be reprogrammed.
To erase data from it, expose it to ultra violet light. To reprogram it, erase all the
previous data.
 EEPROM (Electrically erasable programmable read only memory) – The data can
be erased by applying electric field, no need of ultra violet light. We can erase only
portions of the chip.

7. Writing Data is
Faster
Temporary
Storage
Store Data in
MBs
Volatile
Used in normal
operations
RAM
Writing Data is
Slower
Permanent
Storage
Store Data in
GBs
Non Volatile
Used for startup
process of
Computer.
ROM

8. 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

9. Parameter Primary memory Secondary memory
Nature The primary memory is
categorized as volatile &
nonvolatile memories.
The secondary memory is
always a non-volatile memory.
Alias These memories are also called
internal memory.
Secondary memory is known as
a Backup memory or Additional
memory or Auxiliary memory.
Access Data is directly accessed by the
processing unit.
Data cannot be accessed
directly by the processor. It is
first copied from secondary
memory to primary memory.
Only then CPU can access it.

10. Formation It's a volatile memory meaning
data cannot be retained in case
of power failure.
It's a non-volatile memory so that
that data can be retained even
after power failure.
Storage It holds data or information that
is currently being used by the
processing unit. Capacity is
usually in 16 to 32 GB
It stores a substantial amount of
data and information. Capacity is
generally from 200GB to
terabytes.
Accesses Primary memory can be accessed
by the data bus.
Secondary memory is accessed by
I/O channels.
Expense Primary memory is costlier than
secondary memory.
Secondary memory is cheaper
than primary memory.