DOOM will freeze on occasion, precisely four times, then continue on
   normally.
   
   John Goulden enlightened me on this behaviour. I used to think it had
   something to do with the VGA BIOS emulation or such stuff, but when I
   saw games like System Shock still animating some parts while freezing
   during game play, I thought it had to be something else. John says:

This will also happen if network drivers are loaded but no network is
connected. If the 'stutter' occurs four times in rapid succession, at
intervals of precisely ten minutes, it is very likely Windows 95 polling
for the nonexistent network. Remove the unneeded drivers and the problem
goes away.

   I wondered why this didn't happen on a non-networked machine.
   
   Specifically, it seems to happen on systems that run Client for
   NetWare. The pausing might come from the client trying to reconnect to
   disconnected servers, or otherwise polling for a nonexistent network
   or server. Likewise, this pausing won't happen if you only have the
   Dial-up Adapter and TCP/IP protocol (No clients or services).
   
   This problem only seems to happen with DPMI games; particularly those
   that use the DOS4GW extender.