[email protected](0333-4461420)1 Storage of Data Instructions and data are held in main memory which is divided into millions of addressable storage

[email protected](0333-4461420) 1

Storage of Data

Instructions and data are held in main memory which is divided into millions of addressable storage units called bytes.

One byte can hold one character One byte can hold 8 bits Computers work by using pulses of voltage which

represent either 1 or 0 A low voltage mean 0 and high voltage mean 1 Total bytes in main memory referred to as the

computer’s memory size.


Bits

Computers use electronic circuits to perform the tasks they are programmed to complete.

These circuits can be in one of two states - ‘On’ or ‘Off’.


Memory Sizes measurement

I nibble = 4 bitsI byte = 8 bitsI kilobytes (kb) = 1024 bytes1 Megabytes (Mb) = 1024kilobytes1 gigabytes (Gb) = 1024Megabytes1 terabytes (TB) = 1024Gigabytes


Memory ( Main store)

Memory is the name given to the group of chips inside the processing unit

The data held in the memory is available to the computer Memory is used to hold following information Programs Input data Working Area Output data There are two types of main memory Ram (Random access memory ) ROM (Read only memory )


RAM & ROM

Ram Its temporary memory Read and Write data Data can be changed

or deleted It is a Volatile memory The instructions

written in Ram at the time of execution

ROM Its Permanent memory It can only be read Data can not change or

deleted It is non Volatile The instructions are

written into Rom at manufacturing time. (BIOS)


Memorytypes

RAM ROM

SRAM DRAM PROM EPROM

Volatile Non-volatile

Semiconductor


PROM & EPROM

PROM Programmable read only

memory User can write instruction

only one time Instructions can not be

erased If there is error while

writing on PROM ,it becomes unusable

EPROM Erasable programmable

Rom User can write instruction

many times Instructions can be

erased If there is error while

writing on EPROM, it can still be used again


SRAM & DRAM

SRAM Static Random Access

Memory It can store its value

without any need to refresh the data as long as the power is available

It utilizes less power It is more expansive

DRAM Dynamic Random

Access Memory It has to be refreshed

after each read operation.

It utilizes more power It is less expansive


Floppy Disk

Used to transfer small amount of data between computers

Come with 3.5 inch disk drive Floppy disk is the hard case the disk inside in

floppy Magnetic disk store binary data as a magnetic

pattern on the disk surface It hold 1.44mb of data Before the data is stored on a disk the disk

needs to be formatted


Hard drives

Consist a several disks on a single spindle

Each disk surface able to store data Each surface can have its own

read/write head This enables the read/write heads to

operate simultaneously which means that the data can be transferred more quickly than by using the large disk

Hard disk is available in all sorts of sizes

A typical computer will have a hard disk capacity of around 20 GB


Hard Disk Mechanism


Magnetic Tape

Large spools of tape are used very large computer systems that need to hold huge amount of data

They are not as common as they used to be They look similar to audio cassettes except

they are larger Their main use is for making backup copies

of hard disk


CD-ROM Drives

Use the same technology as music CD and CD players

The data is stored on the disk digitally and a laser beam is used to read the disk

Light is used to read the disk the data may be packed closely and disk therefore has a huge capacity

Are included in multimedia system CD-ROMs can be filled with clip

art ,encyclopedia ,photograph and all sort of data Are read only disk A CD holds around 600MB data


CD-R

A CD recordable (CD-R) drive has a read/write capability.

Using this device you can write around 15 minutes

CD-R can be used to back up hard drives.Standard CD-R disks can be written to

only once but there is a type of disks can be written, erased and rewritten

They are more expensive than CD-R disks


Digital Versatile Disks (DVD)

Are similar to CD-ROMs in that they look identical and are used to store lots of date.

Like CD-ROM they can be used to store computer application software, multimedia programs and full length movies

This is because CD-Rom typically store 650 MB of data whereas to a DVD stores between 4.7 GB

DVDs also are used to store movies where they produce much better quality pictures and sound compared to a normal video tape.

A film stored on DVD can even be made to offer the viewer a choice of several languages in which it can be played back


Backup devices

It is important to take regular backups of both data and programs for security purposes.

Floppy disks do not have a very high storage capacity and so are seldom used for backup.

Instead higher capacity and faster storage devices are used and main ones are as follows

Tape streamers Zip drives Jaz drives


Tape streamers

Are devices used to backup the data contained on hard drives

Zip Drives Are useful for backing up hard drives They are high storage capacity floppy disks

which are slightly larger and twice as thick as normal floppies

They can typical store data 100 MB or 250 MB


Jaz Drives

Is a removable disk drive which is very fast at transferring data.

Each disk hold up to 2 GB of data The higher data transfer rate means that

they can be used to backup data in a very short time

They can be used for everyday storage just like an ordinary disk drive

Documents

[email protected](0333-4461420)1 Storage of Data Instructions and data are held in main memory which is divided into millions of addressable storage