Computer Storage Devices

Measure of Digital Information

1 bit is the smallest amount of digital information on a computer. One bit is needed to hold either a 1 (a switch that is "ON") or a 0 (a switch that is "OFF") in memory. This is the smallest unit of computer memory.

1 Byte is a group of 8 bits, this is the amount of storage space needed to hold one character

1 Kilobyte (K) = 210 = 1024 Bytes

1 Megabyte (MB) = 1024 KB = 220 = 1,048,576 Bytes

1 Gigabyte (GB) = 1024 MB = 230 = 1,073,741,824 Bytes

1 Terabyte (TB) = 1024 GB = 240 = 1,099,511,627,776 Bytes

Hard Disk Drive (HDD)

In most computers, information is saved to the Hard Disk Drive (HDD) and remains there ready to be used at any time. Applications and other program software may also be stored on the hard disk.

Hard Disk Drives can contain hundreds of Gigabytes of information, and the capacity of the HDD supplied as standard with a computer is rising verys fast. A computer, such as a laptop, will usually be sold with a one HDD as an internal component, however, a supplementary HDD can be added as an internal or external unit; the external drive unit being significantly more expensive. The cost of HDD's increases with capacity.

A hard disk drive with a storage capacity of few GB can store a huge quantity of data. The average multimedia computer currently (2012) on sale will have an internal HDD of between few hundreds GB to 4 TB.

Compact Disk (CD)

Compact Disks (CD-ROM) have been used as computer storage devices , as Read Only Memory (ROM). Users had access to already stored information which can be "read" only. The early CD-ROMs were able to store few hundreds Megabytes of information. CD-ROMs are typically used to store large amount of data such as computer software, graphics files, encyclopaedia, reference manuals, music, videos, films.

Technological developments however have enabled the saving of data to CD-ROMs in the same way as to a HDD. Disk drives are available in two forms: CD-R (Recordable) and CD-RW (ReWriteable). The CD-R disks can only have data saved to them once and it becomes permanently located in that CD. However CD-RW disks allow data to be saved and rewritten as many times as needed. CD-RW drives are to be found in most new computers.

Digital Video Disks (DVD)

DVD's are disks with a storage capacity of few Gigabytes, that can used to store audio, video or computer software. DVD-R is a disk to which information is written once, while information may be written and rewritten many times to DVD-RW.

USB flash drives

USB flash drives are used to store large amount of digital information such as video, audio, games, computer software. They are smaller in size but may hold up to few hundreds Gigabytes of digital information.


Random Access Memory is used to hold the programs, data and all information necessary to run a given task.


Read Only Memory is used hold the programs, data and all information necessary to start up a computer.