This document discusses computer memory and storage. It defines primary and secondary memory, and describes their key differences. Primary memory, also called main memory, is volatile and used for processing. It has high access speeds but limited capacity. Secondary memory is non-volatile and used for long-term storage of large volumes of data. Common types of primary memory include RAM, ROM, and cache. Common forms of secondary memory include hard disks, optical disks, magnetic tapes, USB drives, and cloud storage. The document evaluates various storage media and provides details on their characteristics like capacity, access times, and usage.

1. Presented by:
Dashembha Dohtdong
Roll NO: 0810,Mba

2. 1. Computer memory
2. Storage Evaluation Criteria
3. Primary memory
4. Secondary memory
5. Types of Primary memory
6. Types of Secondary memory
7. Contents
8. Sources

3. Data and instructions entered into a computer systems
through input units have to be stored inside the computer
before actual processing starts. Similarly results
produced by a computer after processing have to be kept
somewhere inside the computer system before being
passed on to an output unit. Moreover a computer must
also preserve intermediate results for ongoing
processing.
Storage unit holdS :
 Data and instructions required for processing
 Intermediate results of processing
 Results for output

4.  Storage Capacity: Amount of data that can be stored.
 Access Time: Time required to locate and retrieved
stored data from the storage unit in response to a
program instruction
 Cost Per Bit of Storage: Cost of a storage unit for a given
storage capacity.
 Volatile: Lost of stored data when power is turn off or
interrupted.
 Random Access: If the time taken to access a piece of
data from a storage unit is independent of the location of
the data in the storage unit it is called random access
storage or random access memory(RAM), pseudo-random
access (access time is nearly same for all
location but not exactly same) or sequential access
(access time depends on the location of the data)
property.

5. 1.Primary/main memory:
 Used to hold pieces of program instructions and data,
intermediate results of processing, recently produced
results of those job(s) on which the computer is currently
working.
 These pieces of information are represented electronically
in the main memory chip circuitry and while it remains in
the main memory, central processing unit can access it
directly at a very high speed.
 Its volatile in nature.
 limited storage capacity
 It have random access property.

6.  Holds the program instructions, data and information of
those jobs on which the computer system is currently not
working but needs to hold them for processing later
 Store large volume of data on permanent basis
 It is much cheaper than primary memory.
 Non-volatile in nature
 Have either pseudo-random access (access time is
nearly same for all location but not exactly same) or
sequential access (access time depends on the location
of the data) property

7. I. RAM: Randomly select and used any location of this
memory to directly store and retrieve data and
instructions.
II. ROM:A non-volatile memory chip in which data is stored
permanently and cannot be altered by usual programs.
III. PROM:A user-programmed ROM is one in which a user
can load and store ‘read- only’ programs and data i.e. it
is possible for a user to customize’ a system by
converting his/her programs to micro-programs and
storing them in a user-programmed ROM chip.
once the chip has been programmed, the PROM
becomes a ROM i.e. the information recorded in it can
only be read

8.  Once information is stored in ROM or PROM chip it cannot be
altered.
 EPROM alters this problem
 It is possible to erase information stored in an EPROM chip and
the chip can be reprogrammed to store new information.
 Often used by Researcher and Developer personnel
 When EPROM is in used, Information stored can only be read
 Information remains in chip until it is erased

9.  A very special high speed memory is sometimes used to
increased the speed of processing by making current
programs and data available to the CPU at a rapid rate.
 The CPU speeds are quite high compared to the access
time of main memory.
 Used to compensate for the mismatch in operating
speeds between CPU and main memory whose
 Access time is closed to the processing speed of the
CPU.

10. 1.MAGNETIC TAPE
 Storage medium for large data that are accessed and
processed sequentially.
 Can also be erased and reused indefinitely.
 Storage capacity of a tape = Data recording density *
length
 Data recording density refers to the amount of data that
can be stored on a given length of tape.
 Mounted on a tape drive before it can be used for
reading/writing of information.

11.  It is a thin circular plate made of metal or plastic
 Coated on both sides with a recording material that can
be magnetized
 Direct-access secondary storage device.
 Most popular on-line secondary storage device.
 Old data are erased automatically by recording new data
 Stored data can be read many times without affecting
data

12. I. FLOPPY DISK or DISKETTES:
 Floppy disk is a flat, circular piece of flexible plastic
coated with magnetic oxide.
 So called because they are made of flexible plastic
plates that can bend.
 Introduced by IBM in 1972 and are now produced in
various sizes and capacities by many manufacturers.
 3 ½ inch floppy disk commonly used
 High density storage capacity is 2.88MB.

13.  Primary on-line secondary storage device for most
computer systems today
 TYPES OF HARD DISKS:
 ZIP/Bernoulli Disks: It consists of a single hard disk
platter encased in a plastic cartridge. 100MB
 Disk pack: It consists of multiple (two or more) hard disk
platters mounted on a single central shaft. All the disks
revolve together at the same speed
 Winchester disk :Consists of multiple hard disk platters
mounted on a single central shaft. However, unlike a disk
pack drive, a Winchester disk drive is of fixed type i.e. its
hard disk platters and the disk drive are sealed together

14.  A relatively new secondary storage medium.
 It a promising random access medium for high capacity
secondary storage .
 Can store extremely large amount of data in a limited space.
 Types of Optical Disk:
a. CD-ROM: Compact Disk- Read Only Memory.
b. WORM Disk/ CD- Recordable (CD-R) disks: As the name
implies, data can be written only one on a WORM disk but
can be read many times .
c. CD Read/Write (CD-RW) disk: similar to WORM disk with the
exception that you can erase the previous content and write
on it multiple time.

15.  Designed primarily to store and distribute movies.
 However, it is fast becoming mainstream optical disk as
prices are reducing and need for large capacity storage is
increasing.
 It is similar to CD-ROM in principle but denser in recording
data.
 Storage capacity of single layer disk is of 4.7 GB, and
double-layer disk is 8.5 GB
 DVD has enough space to store movie and support multi-lingual
audio, multiple camera angles, etc.

16.  With the advent of efficient manufacturing technologies,
price of memory chips has fallen considerably. As a
result a new breed of secondary storage devices has
been introduced that not only provides storage but also
applications on top like music player etc.
I. Flash Drive (Pen Drive):
 Compact device of the size of a pen comes in various
shapes and stylish design.
 One can read, write, copy, delete and move data from
the computer’s hard disk drive to flash drive or from the
flash drive to the hard disk drive.
 Storage capacity are 8 MB, 16 MB, 64 MB, 128 MB, 256
MB,512 MB,1 GB, 2 GB, 4 GB, and 8GB.

17.  Flash memory based cards are available as removable
storage device in different types of electronic
equipment.
 Some of the most popular ones are Secure Digital (SD)
and Multimedia Card (MMC).
 Storage capacity ranges from 8 MB to 2 GB.
 In addition to computers, these cards are used in
various types of digital devices such as digital camera
and cell phone.

18.  Huge storage capacity and very small cost per bit stored.
 Use multiple unit of a storage media (such as multiple disks,
multiple tapes, multiple CD-ROM etc) as a single storage device.
 TYPES OF MASS STORAGE DEVICES:-
DISK ARRAY:A set of hard disks, hard disk drive and a
controller mounted in a single box.
AUTOMATED TAPE LIBRARY: A set of magnetic tape, magnetic
drives, and a controller mounted in a single unit.CD-ROM
Juke box: A set of CD-ROM Disks and Drives, and a controller
mounted in a single unit.

19. Thus, Memory storage is among the main part of the
computer system, its storing ability provides a user with
data and information even after many years. Without
memory execution processes would be difficult.
SOURCES:
I. Sinha,P.K,2007, Computer Fundamentals,BPB
Publications, pg. 111-144
II. Internet