Types of Storage Devices

Physical components or materials on which data is stored are called storage media.

Hardware components that read/write to storage media are called storage devices.

Two main categories of storage technology used today are magnetic storage and

optical storage.

Primary magnetic storage

o Diskettes

o Hard disks (both fixed and removable)

o High capacity floppy disks

o Disk cartridges

o Magnetic tape

Primary optical storage

o Compact Disk Read Only Memory (CD ROM)

o Digital Video Disk Read Only Memory(DVD ROM)

o CD Recordable (CD R)

o CD Rewritable (CD RW)

o Photo CD

 

Magnetic Storage Devices

Purpose of storage devices ‡ to hold data even when the computer is turned off so

the data can be used whenever needed. Storage involves writing data to the medium

and reading from the medium. Writing data ‡ recording the data on the surface of

the disk where it is stored for later use. Reading data ‡ retrieving data from the

surface and transferring it into the computers memory for use.

Diskette drives, hard drives and tape drive all use the same type of medium ‡ use

similar techniques for reading/writing data. Surfaces of diskettes and magnetic tape

are all coated with a magnetically sensitive material such as iron oxide.

The principle use to store data is that of polarisation – all the ions in the magnetic

material align themselves in one direction. Just as a transistor can represent binary

“on” or “off”, the orientation of the magnetic field can be used to represent data. A

magnet has one important advantage over a transistor ‡ it can maintain it’s state

without a continual supply of electricity.

Surfaces of disks are coated with millions of tiny iron particles so data can be causes a small current to flow through the head in one direction or the other

depending on the polarity of the field. The disk drive senses direction of flow and

data is sent from the head into memory.

Magnetic Disks

Diskette drives and hard disk drives are the most commonly used storage devices in

PCs. Both fall into the magnetic storage category because they record data as

magnetic fields.

Fundamental differences and similarities between the two:

· A diskette contains a single flat piece of plastic (the disk) coated with iron

oxide enclosed in vinyl or plastic cover. A hard disk contains one or more

rigid metal platters coated with iron oxide permanently enclosed in a hard disk

drive.

· Diskettes are small and portable (they can be removed from diskette drives).

Hard disks are usually built into the computer and are not portable (unless the

computer is). Exceptions are removable hard disks and external hard drives

which can be detached from the system.

· Floppy disks store only 1.44 MB although special floppy disks offer higher

capacity. New hard disks can store several thousand times as much data as a

diskette.

· Hard drives are much faster than diskettes, their disks spin faster and they

locate data on the disks surface in much less time.

Almost all PCs sold today come with a hard disk and one disk drive. Some computers

also feature a third built in magnetic device – a device that uses high capacity floppy

disks