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

[Chuck Guzis]

On 12/9/2005 at 4:13 PM Allison wrote:

>think about it.  It's a microprocessor with a flat 20bit address and
>nothing
>like the 8088.  In some respects is nicer. I had to write a simple
>debugger 
>for it using the host for the IO.  Very ugly and hard to control.

...and only 2 channels of DMA, where the 8237 would give you 4.  One thing
that pretty much doomed it was the announcement of the 80286 with 16M
addressing capabilities, which means the 8089 wouldn't cover the address
space.  The instruction set was basically increment, decrement, add, AND,
OR, NOT and a couple of bit test and set/clear operations--along with the
usual conditional jumps and a CALL, but no stack, no subtract and no
shifts.  Basically a program-it-yourself DMA controller.

Cheers,
Chuck