HB>OS/2 supports four 'priority classes', corresponding to

HB>        1.      Idle Time
HB>        2.      Normal
HB>        3.      Time Critical
HB>        4.      Server

HB>Within each class, there are 32 priority levels. Within the 'Normal'
HB>priority class, the kernel can adjust priority levels to provide tasks
HB>with 'fair' access to the CPU. (This adjustment can be turned off by a
HB>setting in config.sys.) I think that priorities are discussed along
HB>with the DosSetPri() (or something like that) in the Control Program
HB>reference in the toolkit information folder.

It's a pity that good real-time support requires more than just an
ability to set priority levels.

To be *really* effective, the OS should provide priority inheritance so
that when a high-priority task calls a DLL or an OS service (such as
disk or comms I/O), that thread in the DLL or OS inherits the priority
of the calling application.

This way you don't have high priority tasks being blocked by lower
priority tasks when they needn't be.  It's been my experience that under
OS/2 the realtime effectiveness of the system is *greatly* compromised
by the amount of non-interruptable code that executes in the kernal
which causes significant scheduling delays even on high-priority
time-critical tasks :-(

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