Cacheing

• Book assumes that you can only read or write to the external storage in full blocks.

  • This is usually a good model and matches what the operating system usually does.
  • Operating systems don't waste time fetching a single byte for a read request. If you ask for a single byte then an entire record (or more) is read. The single byte is returned and the rest of the data is cached in memory.
  • One of the reasons a modern operating system such as Unix or Window$ XP require so much memory.