Bigger and Bigger Systems

Bigger and Bigger Systems

On the other hand, a gigabyte isn't much data. Commercial databases often consume hundreds of gigabytes. Moreover, as storage becomes cheaper people find new reasons to store greater amounts of data. For example, retail chains often store terabytes (a terabyte is 1000 gigabytes, or 1012 bytes) of information recording the history of every sale made over a long period of time (for planning inventory; we shall have more to say about this matter in "information integration").

Moreover, databases no longer focus on storing simple data items such as integers or short character strings. They can store images, audio, video, and many other kinds of data that take comparatively huge amounts of space. For example, an hour of video consumes about a gigabyte. Databases storing images from satellites can occupy petabytes (1000 terabytes, or 1015 bytes) of data.

Handling such large databases required numerous technological advances. For example, databases of modest size are today stored on arrays of disks, which are called secondary storage devices (compared to main memory, which is "primary" storage). One could even argue that what distinguishes database systems from other software is, more than anything else, the fact that database systems regularly presume data is too big to fit in main memory and must be located primarily on disk at all times. The following two tendencies allow database systems to deal with larger amounts of data, faster.



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