Available No. of Registers

[ram at nucsrl.UUCP]

Hi,
  
   This is my first posting in this newsgroup. So hold your flames if this
is a dumb question.

   C allows "register ......" construct which instructs the compiler
to reserve a machine register to store that value.  Now my question is,
given a fixed number of registers, How many are effectively usable for
the register declaration.  I know this is machine dependent.  Could
somebody say how many register definitions I could use within a block
of code say for a VAX.  And please go on to mention the CPU/Machine that
allows the greatest number and smallest number of such declarations. 

   Is this number fixed or does it change as the program runs.


                                         Renu Raman
                                     ....ihnp4!nucsrl!ram
                                     Northwestern Comp. Sci. Lab