Backing Storage

What is backing storage?

•When the computer is switched off, the contents of main memory are lost unless they have been saved to a permanent storage device.

•Storage device such as hard drives and USB flash drives are used to keep a permanent copy of program and data files.

Types of Storage Devices - Magnetic

•Called magnetic storage devices because their recording surfaces are coated with a material that enables data to be stored digitally by using different forms of magnetisation.

Hard Disc Drives•This is a metal disk with a magnetised

surfaces on which data is stored as patterns of magnetic spots.

•The disks are in sealed units to stop dust and dirt corrupting data.

•They are usually fixed in the computer, but you can get portable external drives.

Magnetic Tape Drives

• Is mostly used for making backup copies of large amounts of data.

• Has to wind through other data on the tape to find the required data.

• This type of access to data is slow and is called sequential access.

• Can be store several terabytes and is relatively cheap.

Types of Storage Devices - Solid State

•Have no moving parts and are made up entirely from electric components.

USB Flash drives•The most common form of portable

backing storage.•Small portable backing storage device

with no moving parts. •Can store large amounts of data, up to

512 Gb.

Memory Cards / SD Cards

•Memory cards are used in digital cameras, digital video cameras and mobiles phones to store and transfer data.

•They can have the capacity of 4,8,16, 32 + Gb

Types of storage devices - Optical•Use Laser technology to store and

retrieve data by burning areas on a disc to create pits and lands to encode data.

CD – ROM•CD-ROM stands for compact disc – Read

only memory.• It is fast and can store up to 700 Mb of

data.• It cannot be written to – the data is fixed at

the time of manufacture. •The data is read by a sensor that detects

laser light reflected from the surface of the disk.

•Has one speed, the read speed.

CD-R•Stands for CD – Recordable – it allows you

to record data Once.

•Once the data is recorded onto it, it works just like a CD – ROM and is read only.

•Has two speeds, Read speed and the write speed.

CD-RW•Stands for CD- Rewritable.•Record data over and over again.•Can be used to make backups of large

files.•Has three speeds, one for writing, one for

rewriting and one for reading.

DVD-ROM•Like a CD-ROM it is read only. •Has a much larger capacity than a CD –

ROM. •Single layer DVD-ROMS have a capacity

of 4.7 Gb.•Double sided, multi-layer DVDs have the

capacity of 17 Gb.•DVD-R - stands for recordable, and can

only be done one. •DVD-RW – data to be stored over and over

again.