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ANGELA MARY G
MBA (EVENING) 2ND
Memory is the most essential part of a computer.
Without memory there would be no computer, as
we know it today.
It is used for storing both instructions to be
executed and data.
This presentation has been developed after an
intensive research on Memory Devices.
The CPU accesses each location in memory by
using a unique number, called a memory address
Central Processing UnitCentral Processing Unit
I.PRIMARY MEMORY OR MAIN MEMORY
Random Access Memory (RAM)
Read Only Memory (ROM)
Level 1 (L1) cache
Level 2 (L2) cache
III. SECONDARY MEMORY
Optical Media Devices
Magnetic Media Devices
Principle: The Closer The Memory Is To The CPU, The
Faster It Is.
Directly or indirectly connected to the CPU via a memory
Comprises of two buses: an address bus and a data bus .
The CPU firstly sends a number through an address bus, a
number called memory address, that indicates the desired
location of data. Then it reads or writes the data itself
using the data bus.
Additionally, A Memory Management Unit (MMU) is a small
device between CPU and RAM recalculating the actual
memory address, for example to provide an abstraction of
virtual memory or other task.
Broadly, the main memory is of two types-
i. Random Access Memory (RAM)
ii. Read Only Memory (ROM).
A RAM memory chip is an integrated circuit
(IC) made of millions of transistors and
This is a type of memory serves as Main Memory
Of A Computer.
It temporarily stores copy of information and files
loaded from a computer hard drive that are
required by a processor.
It is volatile in nature, which means that data will
be erased once supply to the storage device is
RAM stores data randomly and the processor
accesses these data randomly from the RAM
The RAM chips are of two types-
I. Dynamic RAM(DRAM)
A form of volatile memory which also requires the
stored information to be periodically re-read and
re-written, or refreshed, otherwise it would
II. Static RAM (SRAM)
A form of volatile memory similar to DRAM with
the exception that it never needs to be
A type of RAM that stores each bit of data in a
separate capacitor within an integrated circuit.
Its advantage is its structural
simplicity: only one transistor
and a capacitor are required per
bit, compared to four
transistors in SRAM. This allows
DRAM to reach very high
DRAM chips are available in
i. EDODRAM (Extended Data Out DRAM)
ii. SDRAM (Synchronous DRAM)
iii. RDRAM (Rambus DRAM)
iv. DDRDRAM (Double Data Rate DRAM)
Its cells keep the data
valid until it receives an
It has a dual-pipeline
architecture that allows
the memory controller to
simultaneously read new
data while discharging
A pair of 32 MB EDO DRAM modules
SDRAM has a synchronous
interface, meaning that it
waits for a signal before
responding to control
inputs and is therefore
synchronized with the
computer's system bus.
This allows the chip to have a more complex
pattern of operation than asynchronous
DRAM which does not have a synchronized
Pipelining means that the chip can accept a
new instruction before it has finished
processing the previous
It is a type of
the Rambus Corporation
It is fairly fast and has
tried to address some of
the complex electrical and
physical problems involved
Unlike SDRAM, it can
do two operations per
cycle thereby doubling
the memory bandwidth
over the corresponding
It is a type of memory
in which, memory
refreshing is not
It uses flip-flops to
As it takes up more space than
DRAM, it is used for specialized
It is much easier to use and has
shorter read-write cycles
compared to DRAM.
It performs only read
function not write function.
So the data stored in ROM
cannot be modified.
It comes with special internal
electronic fuses that can be
programmed for a specific
Once this pattern is
established it stays in the
unit. Thus, ROM is non-
1. PROGRAMMABLE READ-ONLY MEMORY (PROM)
•This device uses high
voltages to permanently
destroy or create
(fuses or antifuses)
within the chip.
•Consequently, a PROM
can only be programmed
2. ELECTRICALLY ERASABLE PROGRAMMABLE
READ-ONLY MEMORY (EEPROM)
It allows its entire
selected banks) to be
electrically erased, then
rewritten electrically, so
that they need not be
removed from the
computer (or camera,
MP3 player, etc.)
3.ERASABLE PROGRAMMABLE READ-ONLY
It can be erased by
strong ultraviolet light
(typically for 10
minutes or longer),
then rewritten with a
process that again
requires application of
higher than usual
A 32 KB (256 Kbit) EPROM
It is a high speed storage mechanism.
It Can be either a reserved section of main memory or an
independent storage device.
It speeds up access to data and instructions stored in RAM.
It is a portion of memory of SRAM instead of the slower
DRAM. By keeping as much of the information as possible
in high speed SRAM, it avoids accessing the slower DRAM
It works under the same principle, but uses conventional
main memory (DRAM) instead of high speed SRAM. It
improves the computers performance a lot as accessing
data from RAM is much faster than from hard-disk.
Level 1 (L1) cache
Built inside the CPU.
It works at half CPU clock speed.
Level 2 (L2) cache
Built external to CPU, in the motherboard.
It works at the motherboard bus speed.
Nowadays both L1 and L2 are integrated in
the CPU to reduce access time and further
improve system performance.
The whole idea of
memory cache is
to keep staging
and data in a
closer to the CPU.
Disk caches are usually
just a part of main
memory made up of
common dynamic RAM
These devices are used to store large amount of data
It differs from primary storage in that it is not
directly accessible by the CPU. So they need more
access time and thus are much slower.
Per unit, it is typically also an order of magnitude less
expensive than primary storage. Consequently, modern
computer systems have an order of magnitude more
secondary storage than primary storage and data is
kept for a longer time there (such as in hard disk).
It is broadly of two types-
1) MAGNETIC MEDIA
2) OPTIC MEDIA.
Magnetic storage uses different patterns
of magnetization in a magnetizable material
to store data
It is a form of non-volatile memory.
The information is accessed using one or
more read/write heads.
HARD DISKS and FLOPPY DISKS are such
It stores information on
one or more continuously
spinning disks which are
coated with magnetic
Information is recorded
by magnetic heads
called access arms.
These days, hard disks
have storage capacity
between 80 to 300 GB.
It is made of a flexible
substance called Mylar.
It has a magnetic surface
for recording data.
It stores up to 1.44 MB of
It cannot include graphics or
pictures within it.
All floppy disks must be
formatted before data can
be written on it.
Optic devices are generally circular disc which
can contain data encoded in bumps on a special
material on one of its flat surfaces.
The encoding pattern follows a continuous, spiral
path covering the entire disc surface and
extending from the innermost track to the
The data is stored on the disc with a laser or
stamping machine, and can be accessed when
the data path is illuminated with a laser
diode in an optical disc drive
These are broadly of two types-
1) CDs and 2) DVDs
CDs are very cheap and
store up to 700 MB of
They are of three types-
1. CD-ROM (CD Read
2. CD-R (CD Recordable)
3. CD-RW (CD
It is of the same size as a
CD but stores 15 times as
much information, is 20
times faster than it.
It can hold 17 GB of data.
It comes in three varieties-
1. DVD-ROM (DVD Read Only
2. DVD-R (DVD Recordable)
3. DVD-RW (DVD Rewritable)
FLASH MEMORY BLU-RAY DISK
Is a non-
It is a specific type
cards and USB flash
Uses blue-violet laser to
read the disc
stores almost six times
more data than on a DVD
Memory plays great role in computer
systems. As we have discussed, there are
three computer memory types available in
standard computer based on their function
and physical makeup. However, only the main
memory that can be upgraded and changed,
the others comes with the system whether
it is a processor, ROM or graphics card.