Data Storage

3 types of storage to remember

ROM RAM Secondary or backing storage

ROM

ROM is a part of a computer that holds information

ROM contains the information that tells the computer what to do even when nothing is stored on the hard disk

The manufacturer puts data and programs onto the ROM that will tell the computer how to get started when you switch it on and how to load up Windows

ROM is permanent and cannot be written over

ROM stands for ‘Read only Memory’

As ROM is permanent it is called Non Volatile Memory

Before you save data onto the hard disk, where does the computer temporarily keep it?

In its RAM or ‘Random Access Memory’

RAM is temporary memory and if the computer crashes anything held in RAM will be lost – it is called ‘volatile memory’

The more RAM you have, the more things your computer can temporarily remember e.g. you can have lots of programs open containing unsaved work

128 Mb Ram, 256 Mb RAM or 512 Mb Ram are common

RAM

Secondary Storage

Anything that is not stored in ROM or RAM is secondary storage OR backing storage

How many can you think of? Hard Disk Floppy Disk CD DVD Memory Stick (flash memory)

Hard Disk

Rigid circular magnetic plates that store data

The disk rotates at between 5400 and 7200 revolutions and read write heads float above the surface

They are sealed as even a speck of dust will damage the heads

They store huge amounts of data (gigabytes)

Concentric tracks like a record

Data is stored on the sectors

Gaps between sectors

Disks are usually double sided and hard drives contain several disks in a stack

3.5 Inch Floppy Disk

Circular piece of magnetised plastic protected in a hard plastic sleeve with a metal cover

They are portable and cheap but do not hold much data – 1.44 Mb

They are easy to damage and corrupt

Magnetic Tape

When lots of data needs to be stored, companies still use magnetic tape

This is like a video tape and is a cheap option for backup

It is slow to get data back again as you need to wind through the entire tape

Getting data off a tape is called ‘sequential access’

Optical Disks

What is an optical disk? CD Rom CD R CD RW DVD Rom DVD R DVD RW

Optical disks use a laser beam to read and write data

Access is fast as there is direct access

CDs

CD ROMRead only

CD RWriteable CD – you can burn on information BUT only once

CD RWRewriteable CDs are like a hard disk, data can be added and deleted over and over again. RW stands for Read and Write

CDs hold about 650 megabytes of data

DVDs or Digital Versatile Disks

DVD ROMRead only

DVD RAM Read and Write (there are 2 types DVD R and DVD RW)

DVD RWriteable DVD – you can burn on information BUT only once

DVD RWRewriteable DVDs are like a hard disk, data can be added and deleted over and over again. RW stands for Read and Write

DVDs hold about 17 gigabytes of data and are ideally suited to storing films

Flash Memory

A new type of storage, you can now get memory sticks that you can plug into the USB port on computers

They can store varying amounts of information: 32Mb, 64 Mb, 128MB, 256Mb, 512Mb or 1 Gigabyte

Prices vary according to capacity These are set to replace the floppy disk