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                     Copyright © 1996 Mark Russinovich

                       last updated December 31, 1996

 CpuHog - NT System Killer

        Introduction   CpuHog is a 5 line Windows program that will bring
                       an NT system to its knees by setting itself to the
                       highest priority allowable for non-privileged
                       applications, and then sitting in an infinite
                       while() loop. NT is hung so badly by this that it is
                       impossible to even start Task Manager so that the
                       program can be killed. NT does have internal
                       scheduling measures that boost the priority of CPU
                       starved threads (NT considers a thread starved if
                       more than 3 seconds have elapsed since it was last
                       pulled from the CPU), but they are ineffective
                       against CpuHog, because the boost only pushes them
                       to priority 14 whereas CpuHog runs at priority 15.

                       Is this a flaw in NT? If you think that a user with
                       no special privilege should not be able to crash NT,
                       then you think it is.

 Microsoft's Response  Microsoft has fixed the scheduler with a hot-fix
                       that can be applied to Service Pack 2. The boost for
                       starved threads in the fix is to priority 15 (rather
                       than 14). Now Cpuhog can be killed using Task
                       Manager, albeit in several minutes.

        Using CpuHog   Make sure you're ready to hard reset your system and
                       just type "cpuhog".

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