Why Not Store Everything in Main Memory?

• Costs too much. $1000 will buy you over 128MB of RAM or 7.5GB of disk today.

• Main memory is volatile. We want data to be saved between runs. (Obviously!)

• Typical storage hierarchy:

  • Main memory (RAM) for currently used data.
  • Disk for the main database (secondary storage).
  • Tapes for archiving older versions of the data (tertiary storage).

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