Memory

Maninder Kaur
professormaninder@gmail.com

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 The data and Instructions that are entered into the computer by the
input devices needs to be stored in the computer’s memory before
the actual processing.

 And the results after processing and the intermediate results also
need to be stored in the computer’s memory.

 It basically provides the space for storing of the data and
instructions before processing, during processing and after
processing.

 So, Memory is an essential component of a digital computer. It is
required for storage and subsequent retrieval of the instructions and
data.

 There are two types of memory :
Primary Memory
Secondary Memory
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 Primary memory is mainly used by CPU, so it is termed as primary memory. It is
also called main memory.

 Primary memory is a type of memory that is available in the form of silicon
chips. These chips are created by IC by using very large scale integration
techniques.

 It stores data and instructions that are necessary to perform an operation. It
holds both the intermediate and final results of the computer during processing
as the program proceeds.

 Primary memory is typically high speed memory and very costly.

 Primary memory is volatile i.e. the contents are erased when the power is off.

 There are two types of primary Memory:
(a) Random Access Memory (RAM)
(b) Read Only Memory (ROM)

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 In RAM, it is possible both to read data from the memory and to write
data into the memory.

 In random access memory, any memory location can be accessed in a
random way without going through any other location. The access time
is same for each and every memory location.

 RAM is also called read-write memory. RAM is used in computers for
temporary storage of data.

 The major drawback of RAM is that it is volatile i.e. it stores information
as long as the power is supplied to it. Its contents are lost when power
supply is switched off or interrupted.

 Different types of RAM:
Static RAM
Dynamic RAM

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 ROM is a memory that performs only read
operation.

 A ROM is a non-volatile memory. It stores
information permanently. Its contents are not lost
when its power supply is switched off.

 It is not accessible to user, and hence user
cannot write anything into it. ROM is used to store
permanent (fixed) programs.

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 PROM (Programmable Read Only Memory)

 EPROM (Erasable Programmable Read Only
Memory)

 EEPROM (Electrically Erasable Read Only
Memory)

 UVPROM (Ultra-Violet Programmable Read Only
Memory)

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 Secondary memory is also called auxiliary memory.

 It stores information that is not necessarily in current use.

 It is slower and having higher capacity than primary memory.

 This kind of memory is large, slow and inexpensive.

 It is non-volatile storage media i.e. the contents are not erased
when the power is switched off.

 Magnetic tape, floppy disk, hard disk and optical disk are the
examples of secondary storage.

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 Magnetic Tape is a plastic ribbon which is usually ½ inch
or ¼ inch wide & 50 to 2400 feet long.

 It is coated with iron-oxide material.

 It is similar to the tape of audio cassettes of tape recorders.

 Data is stored as binary digits.

 Data is accessed sequentially so searching becomes
difficult.

 Due to their compact size & lightweight it is

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Advantages:
Store data up to few gigabytes
Low cost
Magnetic tape used by both mainframes and
microcomputers

Disadvantages:
Sequential access so searching becomes difficult.
We can either read or write data at one time.

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 Commonly used direct-access secondary storage
device.
 It is a thin, circular plate made of metal & plastic,

which is coated with iron-oxide.
 We can randomly access the data.
 Magnetic disks can also be erased & reused

indefinitely.
 They must be stored in dust free environment.
 It stores large amount of data.

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 The magnetic disks come in different sizes.

 Due to large storage capacity of magnetic disks
and lesser failures the use of these devices
increasing day by day.

 There are two types of Magnetic Disks:
FLOPPY DISK
HARD DISK


 More suitable than magnetic tapes for a wider range of applications
because they support direct access of data

 Due to their low cost and high data recording densities, the cost per bit of
storage is low for magnetic disks.

 An additional cost benefit is that magnetic disks can be erased and reused
many times

 Suitable for both on-line and off-line storage of data

 Floppy disks are compact and light in weight. Hence they are easy to handle
and store.

 Very large amount of data can be stored in a small storage space.

 Data transfer rate for a magnetic disk system is
 normally higher than a tape system


 It is a portable, inexpensive, storage medium that consists of thin, circular,
flexible plastic Mylar film.

 It was introduced by IBM in 1972.

 Standard floppy disk has storage capacity up to 1.44MB.

 Floppy disks are compact, lightweight and easily portable from one place to
another.

 Also known as floppies or diskettes

 Most popular and inexpensive secondary storage
medium used in small computers


Types of Floppy disks:

5¼-inch diskette, whose diameter is 5¼-inch. It is encased in a
square, flexible vinyl jacket

3½-inch diskette, whose diameter is 3½-inch. It is encased in a
square, hard plastic jacket

Advantages

Reusable, portable, Handy.
Very low price
Provide random access of data

Disadvantages

Not Durable
Prone to damage
Very low Capacities


 Round, flat piece of rigid metal (frequently aluminum) disks coated
with magnetic oxide

 It is a storage device that contains one or more inflexible, circular
patterns that store data, instructions & information.

 We can store documents, presentation, database, e-mails, messages,
music , video, software etc.

 Come in many sizes, ranging from 1 to 14-inch diameter.

 Hard disk of capacities 10GB, 20GB, 40GB and even more are easily
available.


 Laser beam technology for recording and reading of data on the
disk.

 Consists of a circular disk, which is coated with a thin metal or
some other material that is highly reflective

 Laser beam technology is used for recording/reading
of data on the disk

 Also known as laser disk / optical laser disk, due to
the use of laser beam technology

 Proved to be a promising random access medium for
high capacity secondary storage because it can store
extremely large amounts of data in a limited space.


 Access times for optical disks are typically in the
range of 100 to 300 milliseconds and that of hard
disks are in the range of 10 to 30 milliseconds.

 The most popular optical disk uses a disk of 5.25 inch
diameter with storage capacity of around 650 Megabytes.

 The optical disk became the preferred medium for music,
movies and software programs because of its many
advantages.

 Compact, lightweight, durable and digital, the optical disk
also provides a minimum of 650 MB of data storage.


 CD-ROM

 WORM Disk / CD-Recordable (CD-R)

 CD-Read/Write (CD-RW)

 Digital Video / Versatile Disk (DVD)

 Blu-ray Disk


 Packaged as shiny, silver color metal disk of 5¼ inch (12cm) diameter,
having a storage capacity of about 650 Megabytes.

 Disks come pre-recorded and the information stored on them cannot be
altered.

 Pre-stamped (pre-recorded) by their suppliers, by a process called mastering.

 Provide an excellent medium to distribute large amounts of data.

 A single CD-ROM disk can hold a complete encyclopedia, or a dictionary,
or a world atlas, or biographies of great people, etc.

 Used for distribution of electronic version of conference proceedings,
journals, magazines, books, and multimedia applications such as video games

 Access time for optical disk is in range of 100 to 300 milliseconds.


 Stands for Write Once Read Many. Data can be written
only once on them, but can be read many times

 Same as CD-ROM and has same storage capacity

 Allow users to create their own CD-ROM disks by using a
CD-recordable (CD-R) drive that can be attached to a
computer as a regular peripheral device

 Data to be recorded can be written on its surface in
multiple recording sessions.

 They are used for data archiving and for making a
permanent record of data. For example, many banks
use them for storing their daily transactions.


 Same as CD-R and has same storage capacity

 Allow users to create their own CD-ROM disks by
using a CD-recordable (CD-R) drive that can be
attached to a computer as a regular peripheral
device.

 Data to be recorded can be written on its surface in
multiple recording sessions.

 Made of metallic alloy layer whose chemical
properties are changed during burn and erase

 Can be erased and written afresh.

 Looks same as CD-ROM but has capacity of 4.7
GB or 8.5 GB

 Designed primarily to store and distribute movies

 Can be used for storage of large data


 The Blu-ray Disc is a technology platform that can
store sound and video while maintaining high quality
and also access the stored content in an easy-to-use
way.

 advantage of Blu-ray Disc's large capacity and high-
speed data transfer rate.

 Large recording capacity up to 27 GB.

 High-speed data transfer rate 36 Mbps.

 Easy to use disc cartridge.


 The cost-per-bit of storage for optical disks is
very low because of their low cost and enormous
storage density.

 Optical disk drives do not have any mechanical
read/write heads to rub against or crash into the
disk surface. This makes optical disks a more
reliable storage medium than magnetic tapes or
magnetic disks.

 Optical disks have a data storage life in excess of 30
years. This makes them a better storage medium
for data archiving as compared to magnetic tapes or
magnetic disks.


As data once stored on an optical disk becomes permanent,
danger of stored data getting inadvertently erased/overwritten is
removed

Due to their compact size and light weight, optical disks are
easy to handle, store, and port from one place to another

Music CDs can be played on a computer having a CD- ROM
drive along with a sound board and speakers.

This allows computer systems to be also used as music
systems


It is largely read-only (permanent) storage medium.

Data once recorded, cannot be erased and hence the
optical disks cannot be reused.

Thedata access speed for optical disks is slower than
magnetic disks.

Optical disks require a complicated drive mechanism.


Memory

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