[TUHS] AT&T Hardware (3B2)

Kevin Bowling kevin.bowling at kev009.com
Mon Jul 2 19:56:33 AEST 2018

I have several working 3B2s and a non-working 3B1 aka UNIX PC/ 7300.

Your story sounds more like a 3B1 where Convergent Technologies was
the ODM (original design mfg).  I've seen Convergent branded 7300s in
collections or for sale.

The various 3b2 models are a relatively simple backplane design, the
cards are all discrete chips on small boards that aren't very dense
integration vs other contemporary systems.  I couldn't see more than a
few manual reworks being more cost effective than reving the PCBs on
it, especially because it was a "serious system".

Wikimedia has a good pic of the first model, 3B2-300, main board

One thing I've desired are contemporary pictures of the 3B5, 3B15 and
3B20 if anyone knows of intact machines.

On Sun, Jul 1, 2018 at 6:29 AM, Steve Johnson <scj at yaccman.com> wrote:
> The 3B2 was designed for AT&T by Convergent Technologies.  I later worked
> with several people at Convergent, one of whom had a framed circuit board on
> his wall.  It was a wonder to behold -- the board had wires all over it that
> were added later, and nearly a dozen "bugs" -- in the days of discrete logic
> chips, a bug was when you took another chip and glued it, upside down, on
> top of an existing chip and then ran wires to the pins in the air.   As I
> recall, the story was that the first demo of the 3B2 happened roughly six
> weeks after the initial request, using the board on the wall.  Now, that's
> what should really be in the computer museums...
> In those days, if there was floating point it was a separate chip, and the
> 3B2 had none.   Floating-point instructions caused a fault, which meant a
> context switch to the OS, where the instruction was emulated and then the
> program returned.   The performance, as I recall was about 800 FLOPS -
> dismal.   We fixed the compiler so it would generate calls to subroutines
> that did the floating point operations, and the performance improved by over
> an order of magnitude -- still dismal, but no longer ridiculous...
> One of the events that led me to leave AT&T was that they fired the head of
> the benchmarking group at Indian Hill, a most competent woman, because they
> didn't like the results she was presenting.  When a company's information
> channels stop functioning reliably, it's time to leave...
> Steve
> ----- Original Message -----
> From:
> "Doug McIlroy" <doug at cs.dartmouth.edu>
> To:
> <tuhs at tuhs.org>
> Cc:
> Sent:
> Sat, 30 Jun 2018 14:24:24 -0400
> Subject:
> Re: [TUHS] AT&T Hardware
> Anent 3B's: Last time I visited Paul Allen's Living Computer Museum
> the only working Unix on display was running on a 3B2. Apparently
> the machine was robust if nothing else.
> doug

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