Vision

The developments described above make heavy requirements of the data storage capacity. Multimedia implies that we have to be able to store, edit and present great quantities of digital data by means of computers. With computers we are dealing with three types of media on which we can store programmes and data: the computer memory, consisting of memory chips, fixed storage media, such as magnetic hard disks connected to the computer, and transportable storage media, such as tapes, floppy disks and different types of optical disks.

Computer Memory
Besides processor chips that carry out instructions, a computer also contains memory chips to store the data and programmes the processor is working with. In the memory chips, we see the same amount of miniaturisation as in the processor chips. Current chips have a storage capacity of 64 Mbit at the most. The next generation of chips will be able to contain 256 Mbit. Further miniaturisation will lead to a storage capacity in the order of magnitude of Gbits.
The storage capacity of memory chips also doubles every two years. If this were to continue until the year 2020, eventually a set of chips the size of a cigar box will have the capacity of the human brain, being 1800 peta(1015)Bytes.
The growth of computer memory makes it possible to place increasingly large objects with the corresponding software functions in the memory and have them executed by the computer.

Magnetic Hard Disks
A computer stores programmes and data it is not working with on magnetic disks that are permanently connected to the computer. The disks may be built into the computer, like the hard disk of a PC, or they may be contained in separate hardware and connected to the computer processor and memory via a fast cable connection.

The standard sizes of magnetic disks are getting smaller and smaller. After 16 inch and 8 inch diameters, the common sizes now are 51/4 inch and 3.5 inch. Even smaller sizes, such as 2.5 inch and 1 inch are already being used. Especially smaller computers and PDAs need smaller hard disks.
A common 3.5 inch magnetic disk nowadays can contain 1 GB of data. Higher values, such as 1 GB on a 1 inch disk or 10 GB on a 3.5 inch disk will be possible soon.
In magnetic disks, too, parallel processing is a possibility to increase the capacity. To this end, the RAID (Redundant Array of Inexpensive Disks) was developed. A set of relatively inexpensive disks is used parallel in a fixed combination. There are different ways to distribute the storage of the data among the disks. There is always a certain form of additional storage (redundancies) so that in case of a breakdown of one of the disk there is always the possibility to reconstruct the contents of the data. Depending on the distribution among the disks, a RAID realises a certain degree of security and faster data access.

Transportable Storage Media
Transportable storage media are tape, magnetic disks such as floppy disks and optical disks (MO, WORM and CD).
Tapes and floppy disks are common media for additional data storage (back-ups of the hard disk) or for transporting data from one computer to another.
The 51/4 inch floppy disk by now has been almost completely replaced by the 3.5 inch disk. The common storage capacity of the latter has grown from 720 Kb to 1,4 Mb. 2.2 Mb disks are also available.

There are three types of optical disks:

• magneto-optical (MO) disks that can be overwritten;
• WORM (Write-Once-Read-Many) disks;
• Compact Discs (CD) in different forms, which can only be read.

The expected storage capacity of a 51/4 inch MO disk is currently 10 Gb. In the laboratories, techniques are now tested to switch individual molecules on and off by means of laser light. If this works, a storage capacity of 10 Gb per cm 2 can be reached. That amounts to 500 Gb on a 3.5 inch disk.
The maximum storage capacity of MO disks is currently 230 Mb for 3.5 inch disks and 1.3 Gb for 51/4 inch disks.

WORM disks are used for electronic archiving of large quantities of data, for example images of paper documents. As magnetic disks in a RAID configuration have become cheaper, the WORM has lost much of its importance. A WORM is useful in situations when people want to be sure that data once written cannot be changed later on.

CDs fall in a different category of optical disks. A CD is produced with a special machine. The oldest type of CD is the 51/4 inch audio CD by Philips, containing approximately 70 minutes of music, digitally recorded. Meanwhile, the CD-I has been introduced, on which interactive audio/video documents have been recorded.
CDs are also used by the computer, in the form of CD-ROM (Read Only Memory). CD-ROMs can be read by means of a special CD-ROM player. The latest PC models often have built-in CD-ROM players. In combination with multimedia, the CD-ROM player is quickly gaining popularity among PC users.
Current CD-ROMs contain 650 Mb of data. Suppliers use CD-ROM to sell large quantities of data, for example software packages, picture libraries for drawing tools, aircraft manuals, catalogues and (interactive) multimedia documents. The capacity of CD-ROM will further increase over the next few years. Through the use of blue laser light instead of red and through further optimisation, the capacity will grow to approximately 5 Gb. A capacity of over 10 Gb can be realised by storing data on a CD in several layers of different colours.

Summary
Storage media will be offering sufficient capacity, even for large multimedia and virtual reality applications. At first, the combination of magnetic disks and RAID technology offers sufficient storage capacity. Later on, optical disks with storage on a molecular level will probably become more important. With the further miniaturisation of the memory chip it is expected that in time solid-state memories based on chips or other technology will become so cheap that they will eventually replace magnetic and optical disks.

In future, transportable storage media such as tapes, floppy disks and CDs will largely disappear. The development of a world-wide data network between business computer systems and home systems will render these media obsolete. Data exchange or the delivery of multimedia documents can then take place via the network.