8" DSDD disk

[Tony Duell]

> Personally I think the basic design of the PC is bad but I've got enough 8" 

Me too... When I got my set of TechRefs, I read through the schematics 
and ROM listings. About every 30 seconds I would exclaim 'They did WHAT???'

> disks that if I could get $20 each I could build a newer better shop to work 
> on my toys I truly love :-}

Agreed...

> 
> I've always thought computers should be built to maximize performance, IBM 
> not only appear to have ignored that but built down.  They took a 5mhz brain 
> dead version of a 16 bit chip and ran it on an 8 bit bus @ 4.77mhz and put a 
> RAM limit of 448mb of RAM.  The excuse of running 4.77mhz was for color 
> burst but I never saw a video card that didn't use its own crystal negating 

The original IBM CGA card (and many clones of it) used the 14.3... MHz 
clock from the motherboard. This was divided by 4 on the CGA card to give 
the NTSC colour subcarrier anr by 3 on the motherboard to give the 
processor clock.

On the AT motherboard (both the 6 and 8 MHz versions) there's a separate 
14.3... MHx oscillator to provide this clock signal. There's a similar 
oscillator on the expansion unit backplane since the 14.3... MHz signal 
is not sent through the expansion cable. AFAIK, though, you can't put the 
CGA card in the expansuon unit (memory accesses to the video address 
range are not passed to the expansion unit), so I guess IBM though this 
signal might be used by something else. I can't think of another IBM I/O 
card that uses it.

> the need for the 4.77mhz.  In any case the extra $0.50 it might add to a 
> video board versus slowing down a $3000.00 computer doesn't make any sense 
> any way.

What makes even less sense to me was missing out the couple of cheap TTL 
chips (literally) that would have let them have active-low 
level-triggered interupts on the expansion slots. Uses had IRQ conflicts 
for ever more.... I once jokingly said that IBM-PC stood for 'Interrupts 
Being Missed, Polarity Corrupted' :-)

Now why Intel sold an interrupt controller with active high inputs is also
beyond me, but then again Intel were not known for good designs (I once
claimed that there wasn't a single Intel LSI chip without a design
misfeature at the time the PC came out...)

> individualism.  It's a shame we didn't have the sense to just say no to 
> Willy.  Please note I have no personal knowledge about the EU constitution, 

I try to. I rarely run MS-DOS, the only version of Windows I have is v1.0 
for the HP150 (!). OK, I've got M$ BASIC in ROM on some of my 8-bitters, 
but I don't depend on those (and other BASICs, like BASIC-09, BBC BASIC 
and HP71 BASIC are much nicer. Heck HP9830 BASIC is nicer than 
Microsoft's offering).

One of the good things about classiccmp (IMHO) is that I can avoid 
Microsoft here 

(This has nothing to do with PDF files, there are plenty of tools for 
creating and reading them on non-Windows machines)

-tony