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Ask the Wizard Questions


The Question is:

What is the granularity of the CLOCK command in VAX
PASCAL, also, what units does it measure?

The Answer is:

    According to the DEC Pascal Language Reference Manual:

"  8.21 CLOCK Function
    The CLOCK function returns an integer value indicating the
   amount of central processor time (in milliseconds) used by
   the current process. This function does not have a parame-
   ter list. The result of CLOCK includes the amount of central
   processor time allocated to all previously executed images."

  That being the case, the value is most likely taken from the system
  clock which is incremented at 10ms intervals - hence the granularity
  will be 10ms. A simple program seems to support this:

VAR LastTime,NextTime : INTEGER;

  UNTIL LastTime <> NextTime;
  WriteLn('LastTime = ',LastTime,' NextTime = ',NextTime);
$ run checkclock
LastTime =    3495890 NextTime =    3495900

  Note however that the granularity may vary in future as OpenVMS is capable
  of expressing times to an accuracy of 100ns.