The document summarizes the different types of computer memory. It describes primary memory (RAM and ROM) and secondary storage. RAM is volatile and temporarily stores active data and programs, while ROM is non-volatile and stores permanent instructions. RAM types include SRAM and DRAM, while ROM types are PROM, EPROM, and EEPROM. Secondary storage is non-volatile and stores long-term data at a lower cost than primary memory.

1. PRESENTED BY
VANITHA KUMARI. R MCA

2.  The computer system essentially comprises
three important parts – input device, central
processing unit (CPU) and the output device.
 The CPU itself is made of three components
namely, the arithmetic logic unit (ALU),
memory unit, and the control unit.
 In addition to these, auxiliary
storage/secondary storage devices are used to
store data and instructions on a long-term
basis.

3.  The Term Computer Memory is defined as one
or more sets of chips that store Data/program
instructions, either temporarily or permanently.
 It is critical processing component in any
computer. The PCs use several different types
of memory.

4.  Secondary Memory/Auxiliary Memory
 Primary Memory/Main Memory
-RAM
*SRAM
*DRAM
-ROM
*PROM
*EPROM
*EEPROM

5.  The computer usually uses its input/output
channels to access secondary storage and
transfers the desired data using intermediate
area in primary storage.
 It is typically used as a supplement to main
storage. Secondary storage does not lose the
data when the device is powered down—it is
non-volatile.
 Per unit, it is typically also an order of
magnitude less expensive than primary storage.

6.  Primary storage (or main memory or internal
memory), often referred to simply as memory, is
the only one directly accessible to the CPU.
 Main memory is directly or indirectly connected to
the CPU via a memory bus. It is actually two buses
an address bus and a data bus. It reads or writes the
data itself using the data bus.

7.  RAM or Random Access Memory is the central
storage unit in a computer system. It is the place
in a computer where the operating system,
application programs and the data in current use
are kept temporarily so that they can be accessed
by the computer’s processor.
 The data stored in RAM is lost if the power to the
IC chip is disconnected. Random access memory,
also called the Read/Write memory, is the
temporary memory of a computer. It is said to be
‘volatile’ since its contents are accessible only as
long as the computer is on.

8. Static RAM (SRAM)
 The information remains stored as long as
power is applied to the chip, unless the same
location is written again.
Dynamic RAM (DRAM)
 The data stored at each location must be
periodically refreshed by reading it and the
writing it back again, or else it disappears.

9.  ROM or Read Only Memory is a special type
of memory which can only be read and
contents of which are not lost even when the
computer is switched off.
 It typically contains manufacturer’s
instructions. Among other things, ROM also
stores an initial program called the ‘bootstrap
loader’ whose function is to start the computer
software operating, once the power is turned
on.

10. PROM
EPROM
EEPROM

11.  Information once stored on the ROM or PROM
chip cannot be altered.
 One step up from the masked ROM is the PROM
(programmable ROM), which is purchased in an
unprogrammed state.
 The process of writing the data to the PROM
involves a special piece of equipment called a
device programmer.
 The device programmer writes data to the device
one word at a time by applying an electrical charge
to the input pins of the chip. PROMs are also
known as one-time programmable (OTP) devices.

12.  EPROM (Erasable PROM) allows a user to
erase the information stored on the chip and
reprogram it with new information.
 An EPROM is programmed in exactly the
same manner as a PROM. However, EPROMs
can be erased and reprogrammed repeatedly.
 To erase an EPROM, we can simply expose the
device to a strong source of ultraviolet light.
By doing this, we essentially reset the entire
chip to its initial-unprogrammed-state.

13.  EEPROMS are electrically-erasable-and-
programmable. Internally, they are similar to
EPROMs, but the erase operation is
accomplished electrically, rather than by
exposure to ultraviolet light.
 Any byte within an EEPROM may be erased
and rewritten. Once written, the new data will
remain in the device forever-or at least until it
is electrically erased.