[rescue] Cheapass MicroFax (sic)

Dave McGuire mcguire at neurotica.com
Fri Jan 24 15:55:07 CST 2003

On Friday, January 24, 2003, at 04:41 PM, Bill Martin wrote:
>>   ...or you can just post here.  There are lots of DECheads here.  
>> The pdp11 field guide covers many boards which can be used in both 
>> PDP11 and VAX systems.
> Both?  Are they 16 bit, or do they somehow autodetect?

   Qbus is a 16-bit data bus with either a 16-, 18-, or 22-bit address 
Only some machines actually put the memory on Qbus...most of the Qbus 
PDP-11s do, except for the 11/83, /84, /93, and /94.  The only Qbus VAX 
that goes through Qbus for memory access is the MicroVAX-I.  The other 
machines use a PMI (Private Memory Interconnect) of one sort or 
another.  See that ribbon cable connecting the KA640 to its memory 
board(s)?  That's the PMI.

>   Wasn't the Vax a clean sheet architecture hardware-wise? (I have a 
> lot to learn.  Great fun!)

   Processor architecture != bus interface.  The first VAX, the 11/780, 
used Unibus as its I/O bus.  Later VAXen used Qbus, BI, XMI, and 

> And I thought Sun SPARC boxes were well built.  I'm impressed, though 
> I was already impressed by the PWS433au I bought a couple of months 
> ago.

   Ahh, even the PWS machines are *nothing* compared to this.  Right 
down to the thickness of the metal in the chassis.

>   Can you tell by now that I'm an engineer?  Retired now, got into 
> management in later years, but once an engineer...  (Yes, I confess my 
> sellout, a suit.  But it is/was mechanical engineering, so I had 
> nothing professionally to do with computers except as a user and when 
> experiencing jealousy (imagining the MIS (remember MIS?) guys' fun) 
> and frustration (when they wouldn't let me do what I wanted.  Like buy 
> a CP/M box.  Though they did give me the first PC in the company 
> (Southern Railway.))  So please, no flames.)

   We forgive you.  This time. ;)


Dave McGuire           "Wear whatever you want...Just don't be surprised
St. Petersburg, FL        if you wind up with a blow-gun dart in your
                            prosthetic boobies."    -Kurt Huhn

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