Subject:   -27- Frame control on low- and mid-range machines
Date: 8 Apr 1994 00:00:01 EST

  Currently, the video clock (pfInitVClock, pfGetVClock, pfVClockSync)
  is supported only on systems with VGX, VGXT, RealityEngine,
  RealityEngine2, Elan, XS, and Extreme graphics hardware.  On other
  systems, pfVClockSync returns immediately.  Because libpf normally
  uses pfVClockSync for frame rate control, frame control is not
  rigorous on other platforms.