Okay, I've browsed a bit through "Inside Windows 2000" and tried to summarize just a little part of
Thread Scheduling from Chapter 6.
A thread runs for an amount of time called a "Quantum". A thread will always be interrupted at the end of it's Quantum, and NT will then check if there's a higher-priority thread that needs to be scheduled, or if the current thread's priority needs to be reduced (there's some dynamic priority levels in NT).
A thread isn't guaranteed to run for it's entire quantum, though - it can even be pre-empted before it's quantum starts. This is because higher-priority threads are always given preferance.
NT schedules strictly at thread granularity,
no consideration is given to what process the thread belongs to. - so yes, an app with 10 threads could "starve" an app with 2 threads. So you need to do responsible design; don't have a bunch of CPU-intensive threads on a single-CPU system. Having multiple threads isn't a problem as long as most of the threads are blocking for events, though, since those won't even be considered for scheduling.
In most OSes, everything in "kernel mode" (which includes the drivers and the kernel/monitor) are mapped together such that execution can move from one place to another without the overhead a protection switch. (Yes, that means a bad driver can crash the kernel.) Does Windows work the same way?
Yup, everything kernel-mode is basically lumped together in the high part of the address space (upper 2GB, unless a boot.ini switch is added to make the split 3GB for usermode and 1GB for kernelmode). So the kernel part, afaik, stays mapped in every process.
Well, you run out of MMU register pairs for each separately protected module that must be constantly mapped into memory. How many MMU mapping registers does the Pentium processor have?
x86 doesn't work that way
You have a register (CR3) that points to a page table (physical memory address). Each process has it's own CR3 value. The page table is a multi-level hierarchy that maps linear->physical addresses, including some additional info like access rights (since pages are 4k and must start at 4k boundaries, there's 12 bits for per-page stuff). There's also some extensions that allow for 2MB and 4MB pages, but 4kb is by far the most common and useful granularity.
That was a
very rough breakdown
NT doesn't do "swapping", it does "paging" - ie., it swaps individual pages in and out, instead of full processes.
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