Legacy apps in Windows/OS X was Re: Old MS-DOS & Win Software

[woodelf]

Jim Leonard wrote:

> woodelf wrote:
>
> For the 8088, and its implementation in the IBM PC 5150 and 
> compatbiles, the timings in the opcode tables are indeed correct -- if 
> the instructions are already in the prefetch queue.  The 8088 only has 
> a prefetch queue of 4 bytes, so if your instructions aren't already 
> prefetched it will take 4 cycles per byte for the Bus Interface Unit 
> to fetch them.  For example, "POP reg" is listed as taking 8 cycles, 
> but if it's NOT been fetched it takes an additional 4 cycles to read 
> the opcode itself.  So the total time if not prefetched is actually 12 
> cycles.

I thought the pre-fetch queue was longer than that. Still most 
instructions  I bet are 3 to 4 bytes long when you
have to  acess memory.  I  just  tend  to count memory cycles on 
instructions for ball park timing.
What I do find odd that the 8086 came out first then a few years later 
the 8088.
It still think the 8086/8086 could have had two instruction sets -- 
8080  emulation and
a better 16 bit design.