Data storage

A computer has two different types of storage:

1. the computer's memory (ROM and RAM)

2. a backing store

1. The computer’s memory – ROM and RAM

1.1 ROM

Read Only Memory (ROM) is computer memory that normally cannot be changed by a program or user. The data stored in ROM stays the same even after the computer is turned off. For example, ROM stores the instructions for the computer to start up when it is turned on each time. Some newer computers may have ROM that can be changed by running a special utility program.

1.2 RAM

Random Access Memory (RAM) is a very fast temporary area where programs and data are stored only when the computer is switched on. For example, when you load a word processing program it is loaded into RAM. If a computer is to be used for several tasks at the same time (multi-tasking) adding extra RAM will usually speed up the system as this will provide more temporary storage for program instructions etc. Cost (Oct 2005) from around £22 for 512 Mb RAM.

2. Backing store

2.1 Magnetic disks

Magnetic disks are the most common backing storage medium. Magnetic disks include 3.5-inch portable floppy disks and also the hard disk drive fixed inside your computer.

2.1.a Floppy disks


Floppy disk	Floppy disk drive

You can read data from and write data onto a floppy disk. Floppy disks can be moved between computers and usually store up to 1.44 Megabytes (Mb) of data. Cost (Nov 2003) approx. £5 for a floppy disk drive. A box of 10 floppy disks can also cost around £5.

They can be used for small files in three ways:

	to transfer small files of data from one machine to another
	to back up important small files that are stored on your hard disk
	to store restricted small files that you don't want all other users of your computer seeing

2.1.b Hard disks or hard drives

Hard disks have storage capacities thousands of times larger than floppy disks. Data can be transferred to and from a hard disk much more quickly than from a floppy disk. The cost of data storage using a hard disk has come down in recent years. For example, in October 2005 a 40 Gb (Gigabyte) hard disk could be bought for as little as £25.

Your hard disk will be where you store:

	the operating system software (eg. MS-DOS or Windows XP)
	application programs (such as Microsoft Word, Excel, Access, PowerPoint etc.)
	the majority of your data files (such as word processor documents, spreadsheet worksheets etc)

2.1.c Zip drive

These drives are similar to floppy disk drives – and are convenient for transferring data files from one computer to another – the disks used in them can store much more data. The example here can store 250 Mb of data (about the same as 170 floppy disks) but the disks used are expensive and this type of storage is not as popular as when first introduced – possibly because optical disks are cheaper and can store even more data. Another problem is that they are not installed on every computer system – so users will need to make sure that all the computers they use have these disk drives installed.

2.2 Optical disks

2.2.a CD-ROM (Compact Disk Read Only Memory) disks are optical disks that use the same technology as musical compact disks. They store up to 700 Mb of data and a laser beam is used to read the data off the disk.

Data is written onto the CD-ROM disk before it is sold and cannot be changed by the user. As CD-ROMs are much bigger than floppy disks, they can be used for multimedia applications such as encyclopaedias and can store pictures, sounds and video clips. Cost of drive (Nov 2003) from around £12+.

2.2.b CD-RW (Compact Disk Read Write) Many computers now include a CD Writer and Rewriter (CD-RW). This enables the user to save files onto a CD-RW disk in the same way that they would save them onto a floppy disk (see above). The storage capacity of each disk is around 700 Mb – so they are useful for keeping backup copies of data and other files. These types of drives cost from about £25+ (Nov 2003).

2.2.c DVD-ROM (Digital Versatile Disk Read Only memory) is a replacement for the CD-ROM found in virtually all modern computers. A DVD-ROM disk can store up to 4.7 Gigabytes (Gb) of data – about as much as 8 CD-ROM disks or 3200 floppy disks! Advantages are the greatly increased storage capacity and a higher playback speed. DVD-Video discs can also be played back using a computer DVD-ROM drive.

2.2.d DVD-RW (Digital Versatile Disk Read Write) – like the CD-RW, DVD-RW allows the user to save files onto the special DVD-RW disks. When first introduced these drives cost around £1000. In November 2003 they cost around £80+ . The cost in October 2005 was as little as £25. One advantage is that they can read and write to CD-R; CD-RW, DVD-R and DVD-RW disks.

2.3 Magnetic tape

Magnetic tapes or cartridges are principally used for backup. As they are small, robust and portable, with the ability to store far more than a floppy disk, they are often used to back up important documents and files from the hard-drive. Magnetic media is also used for long-term storage and the archiving of data.

2.4 Flash memory - memory sticks

This is a new type of storage device that is likely to become very popular. It is small, convenient and will store many data files. The user inserts the memory stick into a USB port on the computer – and can save files/open files stored on the memory stick like any other storage medium. Cost around £19 for a 512 Mb stick (Oct 2005)

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