IBM PC hacking

[Scott Stevens]

On Wed, 28 Sep 2005 17:34:46 -0500
Jim Leonard <trixter at oldskool.org> wrote:

> Cameron Kaiser wrote:
> >>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
:-)
> > 
> > I have to admit, even though I'm not a PC fan by any means, I found
the PCjr
> > fascinating. It didn't deserve the fate it got (though it *did*
deserve a
> > better price point than it was saddled with).
> 
> I have several, as I've always found them fascinating:
> 
> - They had diagnostics, BASIC, a "game" and other stuff in ROM
> 
> - They introduced 16-color graphics and 3-voice sound to the world of
PC games, 
> however it was Tandy's CLONE of those graphics and sound that became
popular 
> and advanced the industry
> 
> - To reduce costs, the case of the PCjr is not metal but plastic
coated in 
> metal -- IBM patented a new process to do this (I'm not sure if they
sprayed it 
> on or if it was dipped)
> 
The PCjr also lacked a DMA controller.  So all diskette data has to pass
through the CPU's accumulator, which makes it significantly slower than
a PC-XT.  I remember running a Norton SI on my Junior.  It had a SI of
.7 which was actually 'inflated' since that rating didn't benchmark the
abcence of DMA.  

I used to enjoy playing '3-Demon' on the Junior.  3-Demon was a
'wireframe' 3-D version of Pacman.  If you turned down a row that was
the full legnth of the maze, the machine markedly slowed down as it
struggled to render the deeper wireframe graphics.  3-Demon was a truly
advanced graphic application to run on a first-generation PC.