Local Area Network(LAN) present a cost-effective multi-user environment in which computer and applications can be used to best effect.   CD-ROM networks offer many of the same advantages of conventional LANs.

At the heart of the network lies an optical server which dynamically distributes requested information from CD-ROM drives to LAN users. The optical server is connected directly to CD-ROM drives, with some installation totaling 64 drives per server.

There are several commercially available CD-ROM networks packages, many of  which are software orientated. These are intended for installation on a LAN already in place, and run alongside the accompanying networking software. For example, Opti-Net from Online Computer System Inc., runs on the Novelle network.

Retrieval Systems

CD-ROM data can only be made available through an appropriate retrieval system, of which many well-known implementations exist. A retrieval system takes the form of a program distributed on the disc itself and is most often installed to hard disk for the benefit of increased speed of operation.

The combination of an exceptionally large amount of information, long access time and slow data transfer rate, renders retrieval system design of critical importance. Often providing a means of navigation, its suitability to the task in hand is just as important as the CD-ROM data itself.

As one would except, retrieval system are specific to applications, where the underlying design features vary considerably. At the simplest level, negotiating a telephone directory on CD-ROM merely requires the entry of simple search criteria. Wildcards or Booleans logic may also play a role. Such system are termed target systems, and are useful for database applications.

Data Storage

Having looked at Mode 1 and Mode 2 discs and how average data transfer rates and data capacities are calculated, it is clear that drive specifications are really quite vague.

Because CD-ROM drives are products of standardization and therefore markedly similar, efforts to improve the performance of a program or application on invariably lie in optimizing the data structure and retrieval software design. However, the developer cannot always be expected to understand the precise way in the relevant replication company is willing to pass on appropriate information and to give advice on software to be used in conjunction with data.

For example, data blocks residing in outer turns naturally fall victim to increased latency period, thus imposing a detrimental effect on access time. It is also important to note that, because discs are encoded at a uniform density, when filled to capacity, the greater proportion of disc data will occupy outer turns. Keeping related data in close proximity is also important, as this also reduces the average access time.