IBM PC hacking

[Jim Leonard]

Tony Duell wrote:
>>IIRC, a PS/2 model 25 and 30 also have BASIC in ROM.  And a PCjr most certainly 
>>does (along with a full diagnostic program and "keyboard tutorial" -- the diags 
>>were impressive for the time).
> 
> The problem with those diagnostics (and most built-in diagnostics) is 
> that a fairly large part of the machine has to be operational (at least 
> the CPU, some memory, ROM, video) for them to be at all useful.

While it is rare that a minor error will surface in, say, the CPU (I have NEVER 
seen a CPU go gradually, like "whoops, now I can't ADD or SHL" -- it's all or 
nothing), the diagnostics run in something like 1K of ROM with no memory use 
other than video so they are helpful in diagnosing RAM problems.  And the 
sound, joystick, video, and floppy drive tests are helpful in determining if 
the machine is functional on a basic level -- I always run them on any new PCjr 
I come across to determine if it's worth hauling away or not :-)
-- 
Jim Leonard (trixter at oldskool.org)                    http://www.oldskool.org/
Want to help an ambitious games project?             http://www.mobygames.com/
Or check out some trippy MindCandy at             http://www.mindcandydvd.com/