Computer memory

Introduction of computer memory.

1. Assignment 3:
1) Define the computer Memory.
A Computer memory is just like a human brain. It is used to store data and
instructions. Computer memory is the storage space in computer where data is to
be processed and instruction required for processing are stored. It is an essential
element of a computer. Without its memory a computer is of hardly any use. It
plays an important role in saving and retrieving data. The performance of the
computer system depends upon the size of the memory.
There are various units which are used to measure computer memory. They
are;
 Bit- smallest unit of computer memory
 Byte- 8 bit= 1 byte
 Kilobyte-1024 byte= 1 kilobyte
 Megabyte=1024 kilobyte= 1 Megabyte
 Gigabyte-1024 Megabyte= 1 Gigabyte
 Terabyte- 1024 Gigabyte= 1 terabyte
Computer memory are classified into two types as:
1. Primary Memory
2. Cache Memory
3. Secondary Memory
Primary Memory- Primary Memory is internal memory of the computer. It is also
known as main memory of computer. It is a memory that holds the data and
instruction on which computer is currently working It is the only type of memory
which is directly accessed by the CPU. The CPU continuously reads instructions
stored in the Primary Memory and executes them. Any data that has to be operated
by the CPU is also stored. The information is transferred to various locations
through the Bus. It is fixed in the mother board of the computer. It is such type of
memory without which a computer cannot run. It is working memory of the
computer. Primary memory is of two types. They are:
 RAM
 ROM

2. RAM – It stands for Random Access Memory. Here data can be stored
temporarily, so this type of memory is called temporary memory or volatile
because when power fails the data from RAM will be Erased. The information
stored in the RAM is basically loaded from the computer’s disk and includes
information related to the operating system and applications that are currently
executed by the processor. RAM is considered random access because any
memory cell can be directly accessed if its address is known. The more RAM a
computer has, the more data a computer can manipulate. RAM is further classified
into two parts as:
 SRAM (Static RAM)
 DRAM (Dynamic RAM)
1. SRAM - SRAM stands for Static Random-Access Memory. The word
“Static” refers that the memory retains its contents as long as the power is
supplied to it so that’s why we can say this is volatile in nature. It is made of
flipflops and is used for Primary storage. SRAM does not need to be
refreshed periodically. SRAM is faster and more expensive than DRAM.
2. DRAM- DRAM stands for Dynamic Random-Access Memory. It also
contains data only when electricity is available. It is called Dynamic because
it must be constantly be refreshed and loses the data in very short time even
if it continues to have power supplied to it. DRAM needs to be refreshed
periodically due to this, this RAM work slower than SRAM.
ROM- ROM stands for Read Only Memory. In this, the data will be furnished by
the manufactures regarding the system, so this information can simply be read by
the user but cannot add new data or it cannot be modified. ROM is non- volatile
memory that retains data without the flow of electricity. ROM are basically
classified into 3 types as:
 PROM
 EPROM
 EEPROM
1. PROM- PROM stands for “Programmable Read Only Memory”. In this,
when the data is stored then we have no right to Chage or alter any data of it.
In this the data is written by manufacturer company, even we can also
purchase blank PROM chip but it can be programmed by special tool such as
PROM programmers. In general, in PC’S mainly PROM is used because we
don’t have to alter any data to it.

3. 2. EPROM- EPROM stands for “Erasable Programmable Read Only
Memory”. As the word refers “erasable means we can change or erase the
data. So, in EPROM we have right to change the data. In this, we can change
the data with the help of ultra violet rays. EPROM is much expensive than
PROM.
3. EEPROM- EEPROM stands for “Electrically Erasable Programmable Read
Only Memory”. It is such type of ROM which can be erased by electrical
charges. EEPROM can be erased one byte at any time rather than erasing the
entire chip by ultra violet rays.
Cache Memory: Caches Memory is a small-sized type of volatile memory that
provides high speed data access to processor and stores frequently used computer
programs, applications and data. It stores and retains data until a computer is
powered up. It is smallest amount of fastest memory. It sits between normal main
memory and CPU. It may be located in CPU chip or module.
Working of Cache memory: The CPU initially looks in the cache for the data it
needed. If the data is there, it will retrieve it and process it. If the data is not there,
then the CPU accesses the system memory and then puts a copy of the new data in
the cache before processing it. Next time if CPU needs to access the same data
again, it will just receive the data from the caches instead of going through the
whole process again.
Levels of Cache memory: There are three levels of caches memory. They are as
follows:
Level 1 (L1 cache)- L1 is the fastest cache and usually comes within the processor
chip itself. The L1 cache typically ranges in size from 8kb to 64 Kb and uses the
high-speed SRAM (Static RAM) instead of the slower and cheaper DRAM
(Dynamic RAM) used for main memory. It is referred to as internal caches or
primary caches.
Level 2 (L2 cache)- The L2 cache is larger but slower in speed than L1 cache. It
stores recently accessed information. Also known as secondary cache, it is
designed to reduce the time needed to accessed the data in case where data has
already been accessed previously. L2 comes between L1 and RAM(Processor-L1-
L2-RAM) and is bigger than the primary cache (typically 64 kb to 4 MB).
Level 3 (L3 cache)-L3 cache memory is an enhanced form of memory present on
the mother board of Computer. L3 cache memory which is built into the

4. motherboard. It is used to feed the L2 cache, and is typically faster than the
system’s main memory, but still lower than the L2 cache, having more than 3MB
of storage in it.
SECONDARY MEMORY - As we know, primary memory of a computer is
temporary in nature, I.e., it does not retain its contents once the power is switched
off or even if there is a temporary break in power. Thus, the primary memory is
unsuitable for storing large amount of data for a longer period of time. So there
arises a need for a secondary storage. Secondary storage or auxiliary memory
consists of slower and less expensive device that communicate with CPU via main
memory. The secondary memory stores the data and keep it even when the power
fails. It is used to save large data or program or other information. Some of the
main Secondary memory are:
1. Magnetic Disk
2. Floppy Disk
3. Hard Disk
4. Optical Disks
1. Magnetic Disk- Magnetic Disk is type of secondary memory which is a flat
disc covered with magnetic coating to hold information. It is used to store
various programs and files. The polarized information in one direction is
represented by 1, and vice versa. The direction is indicated by 0. Magnetic
disk is less expensive than RAM and can store large amounts of data, but
data access rate is slower than main memory because of secondary memory.
Data can be modified or can be deleted easily in the magnetic disk memory.
It also allows random access of data.
2. Floppy Disk-Floppy Disk is a small plastic disk, coated with a magnetic
material and enclosed in a square plastic casing. It is used to transfer small
amount of data between the computers. They are also used to hold back-up
copies of the data and program. A typical 3.5-inch floppy disk holds 1.44
MB of data. The floppy disk has the disadvantages of limited storage, slow
speed and low reliability compared to other storage devices.
3. Hard Disk- Hard Disk is a mass storage device consisting of one or more
platters. Each platter is a thin, circular metal plate coated on both sides with
a magnetic material. It is sealed inside a metal case to prevent any foreign
material from getting inside, which causes head crash. It provides faster

5. access to data and are capable of storing large quantity of data. Today’s
computers typically come with high storage capacity hard disk.
4. Optical Disk-Optical disk is a glass or plastic disk coated with reflecting
medium. A very fine laser beam is projected on the reflecting surface to read
data from the disk. By detecting the light intensity reflected from the
surface, the information stored on the disk can be accessed. The optical Disk
are commonly used for video and audio applications. The storage capacity of
laser disk is very high and access of information is very fast. CD-ROM
(Compact Disk Read Only Memory) and DVD (Digital Versatile Disk) are
the common type of optical disks.
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