recursive emulation

[Chuck Guzis]

On 01/24/2017 01:50 PM, Pete Turnbull wrote:


>> Many people think Intel was stupid to have the 80186 be incompatible
>> with the PC but they forget that this processor was practically finished
>> by the time the PC came out and was launched just a few months later,

We started getting samples of the 186 in 1981.  It was, as you might
imagine, pretty buggy--IIRC, we were getting a new stepping about every
month for a time.  Some of the bugs were really bizarre, such as DMA
clobbering the SI and DI registers during the DMA operation (at the
conclusion, they were restored correctly, which made tracking that one
down very difficult.)

What many people don't realize is that the 80286 development was going
on in parallel with the 80186.  It was even more buggy, as one might
expect, in the pre-release steppings than the 186.

Had IBM had working samples of the 186, I don't doubt for a second that
they would have used it as the CPU of the 5150--the advantages were too
great to ignore--integrated 20-bit DMA, timers, interrupt controller and
programmable chip selects would have certainly gone far toward reducing
the component count on the PC.

Somewhere along the line, Intel's much ballyhooed 432 platform quietly
sank under the waves (Micro-mainframe).  It was a multi-chip set and
hideously expensive.

The 8086 really was a 1970s CPU.

--Chuck