Hi..
 > Does anyone know what happens when the CPU comes across an opcode that
 > it
 > doesn't understand?  For example, what happens if a 386 tries to run a
 > 486 or
 > a Pentium opcode?
You get an exception. In this case you get exception 6 - invalid opcode, or 
exception 16 - coprocessor error (for floating point opcodes).
This 'feature' is not present on the 8088/8086, however.
A study of the 386 programmer's guide is worthwhile here - you can restart or 
bypass some exceptions, if you exception handler is written well.... or at 
least procvide a graceful exit to dos.
    Craig
--- FMail/386 1.20
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