Computer MEMORY

Presented by:Dashembha Dohtdong

Roll NO: 0810,Mba

1. Computer memory2. Storage Evaluation Criteria3. Primary memory4. Secondary memory5. Types of Primary memory6. Types of Secondary memory7. Contents8. Sources

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

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.

Volati le: 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 i t 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.

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 volati le in nature.

l imited storage capacity

It have random access property.

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-volati le in nature

Have either pseudo-random access (access time is nearly same for al l location but not exactly same) or sequential access (access time depends on the location of the data) property

I. RAM: Randomly select and used any location of this memory to directly store and retrieve data and instructions.

II. ROM:A non-volati le 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. i t 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

Once information is stored in ROM or PROM chip i t cannot be altered.

EPROM alters this problem

I t 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 unti l i t is erased

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.

1.MAGNETIC TAPE

Storage medium for large data that are accessed and processed sequential ly.

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/writ ing of information.

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-l ine secondary storage device.

Old data are erased automatical ly by recording new data

Stored data can be read many times without affecting data

I . FLOPPY DISK or DISKETTES:

Floppy disk is a f lat, circular piece of f lexible plastic coated with magnetic oxide.

So called because they are made of f lexible plastic plates that can bend.

Introduced by IBM in 1972 and are now produced in various sizes and capacit ies by many manufacturers.

3 ½ inch floppy disk commonly used High density storage capacity is 2.88MB.

Primary on-l ine secondary storage device for most computer systems today

TYPES OF HARD DISKS:

ZIP/Bernoull i Disks: It consists of a single hard disk platter encased in a plastic cartr idge. 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 f ixed type i.e. i ts hard disk platters and the disk drive are sealed together

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 l imited 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 mult iple time.

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-l ingual audio, multiple camera angles, etc.

With the advent of eff icient 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 l ike 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 f lash 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.

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.

Huge storage capacity and very small cost per bit stored.

Use mult iple unit of a storage media (such as mult iple 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 control ler mounted in a single unit.

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. 111-144II. Internet