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 ROM Read only CD R Writeable CD – you can burn on information BUT only once CD RW Rewriteable 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 ROM Read only DVD RAM Read and Write (there are 2 types DVD R and DVD RW) DVD R Writeable DVD – you can burn on information BUT only once DVD RW Rewriteable 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