If the underside of the CD-ROM is scratched data may be lost. CD-ROMs have a considerable storage capacity, up to 640 megabytes and are suitable for sending large amounts of data. However, once a CD-ROM has been written it cannot be reused. It is possible to increase the storage capacity of a CD-ROM even more by compressing the data. The data warehouse comprises a number of databases stored in a single area.
All databases are available to the user at a single time.
This means that tables contained within different subject matter databases may be linked together with a common variable and time series data can be easily compiled. Database A database comprises a series of tables containing data. Databases are generally acknowledged as being one of the most efficient means of data storage. The data is organised into a series of relational tables divided into fields and rows. Individual tables are linked together using a common field or a combination of fields called the primary key.