I built my third computer in 1980. Like the second, it
was an S-100 bus machine, this time
with an
Intel 8086 processor. This was very
much cutting-edge technology at the time, and there wasn't even an operating system for it.
For whatever reason, Gary Kildall
of Digital Research wasn't
overly keen on releasing CP/M-86, and so
the offer I had, from a small company
called Seattle Computer
Products, was a two board set with their own operating system
called 86-DOS.
I was a little dubious about that, and some time round October 1980 I called the company and
spoke with Tim Paterson. He told me
that he had absolute confidence that 86-DOS would survive. “We have an order from a really
big company. If I told you how big, you'd know who it was”. The company
was IBM, of course, and 86-DOS developed
into PC-DOS
and MS-DOS. But that wasn't announced
until nearly a year later, and when it was, it was just an 8088 running at 4.77 MHz, no
comparison with my 8 MHz 8086.
This board contains an 8251 USART and some
parallel port that I don't recognize—presumably performed by the SSI chips at right centre.
The AM9513 is apparently a timer chip, and there are
two Intel 8259A interrupt controller
chips, suggesting more than 8 interrupt levels. There's also a (boot?) ROM. What's missing
is the floppy controller. It seems that I now only have one controller board; maybe I
swapped it from machine to machine as I used them. I would certainly have done that with
the terminal. Here's the Delta floppy controller again:
This appears to be a 32 kB board, so it may belong to
the Z80 machine. Some of the chips
have found use elsewhere, but it's interesting to note that it appears to have a parity bit.
I'm not sure which of these I used. They were all based on a
the Intel 8202 dynamic RAM
controller chip, which had the interesting feature of not being fast enough for the chips.
I had untold grief getting the thing to work.
