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 7   Data File Buffering
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     The Clipper 5.0 database drivers use virtual memory segments to contain
     database and index file buffers.  This allows the VMM to manage these
     buffers on a competitive basis with other uses of memory.  As with
     dynamic overlay segments, the VMM will swap buffer segments into EMM
     but not to the disk swap file.  If a VM segment containing a disk
     buffer is to be removed from memory altogether, it is written back to
     the appropriate data file.

     The file buffering system allocates buffer management tables in fixed
     memory (see Fixed Memory Allocator below).  The actual amount used
     depends on the combined total of real memory and EMM available at
     startup.  The tables use 14 bytes per 1K of real or Expanded memory
     (the tables never exceed 8K, however).  Because these tables are
     allocated in fixed memory, they have an effect on the amount of swap
     space available to the VMM.  In some low-memory situations, reducing
     the amount of available EMM may help to avoid swap space exhausted
     errors. (Note: reducing EMM availability may seriously degrade VMM
     performance in very low memory situations due to increased disk
     swapping--see Use of LIM 3.2 Expanded Memory above.)