This document discusses different types of computer memory. It describes primary memory (RAM and ROM) and secondary storage. RAM is volatile and includes SRAM and DRAM. ROM is non-volatile and includes PROM, EPROM, and EEPROM. Hybrid memory types like EEPROM, NVRAM and flash have properties of both RAM and ROM by being writable like RAM but retaining data without power like ROM. The document provides details on the characteristics and uses of each memory type.

1. Memory and its Types
Dr. Ghayoor Abbas Bhatti
Lecturer
BS(H)Computer Science, MHPED, BHPED, M.A
Sociology
CPEHSS UoS, Jamshoro

3. Memory Types
I. Secondary Memory
II.Primary Memory
a)RAM
i. SRAM
ii. DRAM
b)ROM
i. PROM
ii. EPROM
c)Hybrid
i. EEPROM
ii. NVRAM
iii. Flash Memory
d)Cache Memory
e)Virtual Memory

4. What is Memory?
• Computer memory is any physical device
capable of storing information temporarily or
permanently. For example, Random Access
Memory (RAM), is a type of volatile memory
that is stores information on an integrated
circuit, and that is used by the operating
system, software, hardware, or the user.

5. Volatile vs. non-volatile memory
• Memory can be either volatile and non-
volatile memory. Volatile memory is a
temporary memory that loses its contents
when the computer or hardware device loses
power. Computer RAM is a good example of a
volatile memory and is why if your computer
freezes or reboots when working on a
program you lose anything that hasn't been
saved.

6. Volatile and non-Volatile
• Non-volatile memory, sometimes abbreviated
as NVRAM, is memory that keeps its contents
even if the power is lost. EPROM is a good
example of a non-volatile memory.

7. Memory is not disk storage
• It is very common for new computer users to
be confused by what parts in the computer
are memory. Although both the hard drive
and RAM are considered memory, it is more
appropriate to refer to RAM as "memory" or
"primary memory" and a hard drive as
"storage" or "secondary storage" and not
memory.

8. Memory is not disk Storage
• When someone asks how much memory is in
your computer, it is likely between 1GB and
8GB of Random Access Memory (RAM) and
several hundred Gigs of hard disk drive
memory (storage). In other words, You will
almost always have more hard drive space
than RAM.

9. Primary Memory (Main Memory)
• Primary Memory
RAM
ROM
Semiconductor Definition:
• A device for storing digital information that is
fabricated by using integrated circuit
technology. Also known as integrated-circuit
memory; large-scale integrated memory;
memory chip; semiconductor storage;
transistor memory.

10. Characteristic of Main Memory
• These are semiconductor memories.
• It is known as main memory.
• Usually volatile memory.
• Data is lost in case power is switched off.
• It is working memory of the computer.
• Faster than secondary memories.
• A computer cannot run without primary
memory.

11. RAM

12. RAM
• RAM is of two types:
• Static RAM (SRAM)
• Dynamic RAM (DRAM)
SRAM is a type of RAM that stores data using a
static method, in which the data remains
constant as long as electric power is supplied to
the memory chip. This is different than DRAM
(dynamic RAM), which stores data dynamically
and constantly needs to refresh the data stored in
the memory. Because SRAM stores data statically,
it is faster and requires less power than DRAM.

13. Dynamic RAM (DRAM)
• 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

14. ROM

15. ROM
• ROM stands for Read Only Memory. It is type of
internal memory. The data and instructions in
ROM are stored by the manufacturer at the time
of its manufacturing. This data and programs
cannot be changed or deleted after wards. The
data or instructions stored in ROM can only be
read but new data or instructions cannot be
written into it. This is the reason why it is called
Read Only Memory. ROM stores data and
instructions permanently. When the power is
turned off, the instructions stored in ROM are not
lost. That is the reason ROM is called non-volatile
memory.

16. Types Of ROM
ROM is divided into following types:
• PROM
• EPROM
• EEPROM

17. PROM
PROM stands for Programmable Read Only
Memory. This form of ROM is initially blank.
The user or manufacturer can write
data/program on it by using special devices.
However, once the program or data is written
in PROM chip, it cannot be changed. If there is
an error in writing instructions or data in
PROM, the error cannot be erased. PROM chip
becomes unusable.

18. EPROM
EPROM stands for Erasable Programmable
Read Only Memory. This form of ROM is also
initially blank. The user or manufacturer can
write program or data on it by using special
devices. Unlike PROM, the data written in
EPROM chip can be erased by using special
devices and ultraviolet rays. So program or
data written in EPROM chip can be changed
and new data can also be added. When
EPROM is in use, its contents can only be read.

19. EEPROM
EEPROM stands for Electrically Erasable
Programmable Read Only Memory. This kind
of ROM can be written or changed with the
help of electrical devices. So data stored in
this type of ROM chip can be easily modified.

20. Hybrid types
As memory technology has matured in recent years, the line
between RAM and ROM has blurred. Now, several types of
memory combine features of both. These devices do not belong
to either group and can be collectively referred to as hybrid
memory devices. Hybrid memories can be read and written as
desired, like RAM, but maintain their contents without electrical
power, just like ROM. Two of the hybrid devices, EEPROM and
flash, are descendants of ROM devices. These are typically used
to store code. The third hybrid, NVRAM, is a modified version of
SRAM. NVRAM usually holds persistent data.