8-bit OS sought

have

I feel like such a weenie! My first personal computer was a SWTPC 6800 that had a bootstrap ROM. No toggle switches on the front panel for address and data. My greatest hardware accomplishment at that time was to add solenoids and fishing line to an IBM Selectric---which my girlfriend then used to type here MS thesis with a very primitive word processor. I also wrote a simple file system for a fast digital cassette drive that I used for a few years until floppy drives became affordable.

I started real-time programming on a DG Nova machine. It had 5MB

14" disk packs and processor boards made out of TTL logic. The CPU rack was quite heavy. I pulled some muscles severely one time when the unit slid out of the rack somewhat more easily than expected. You seldom had to key in startup sequences, since it used core memory, and you could simply set up the address of the boot loader and hoped it was still in core.

Mark Borgerson

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Mark Borgerson
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No address and data lights, either? Oh, the shame of it all.

Interestingly, I modified an IBM model 85 (?) electronic typewriter by examining all the reed relay signals as I typed keys and documenting them and then designing and hooking up an 8051 CPU to sit in parallel over them so it could replicate the timing required. I then wrote the serial code, with buffering and flow control, so that I could hook it up to my IBM PC and use it as a printer. To my surprise, the whole thing worked the very first time after I carefully wired it up. Whew!

Ah, like a DECTape file system?

I used the 5Mb 14" removable packs on PDP-8s.

Yup. Core memory planes usually included a write-after-read step to restore the value to the memory location after reading it. If it doesn't include this extra circuitry, reading the core destroys the contents -- "destructive read." The PDP-8's accumulator may have used core memory (my memory fails me about whether or not I ever read if this is a fact or simply my conjecture), because the DCA instruction (in effect) wiped the value in the accumulator when it wrote its value to memory.

Jon

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Jonathan Kirwan

You really expect me to remember that? I'm talking ACAD version 1.2 here! I'm still trying to forget the pain! :-)

For example, due to memory restrictions, when doing circuit board layouts we would use "X" blocks (two lines) of different sizes in place of the pads. Pads took too much time to render and too much memory (you could see the circles/squares being drawn. When ready to plot, we'd edit the DXF file by hand (WordStar!) and substitute real pads for the block definitions of the "X"'s. Then you could use the plot command without actually runnning the full AutoCAD package. Living on the edge, that was.

I miss the VT100 terminal though. You kind of get good at typing commands with the left hand while you run the digitizer tablet with the right. Ah, the good old days.

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Martin Euredjian
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Martin Euredjian

And the 8080 before that.

Ian

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Ian Bell
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Ian Bell

Right, but you couldn't hook an 8087 to an 8080. At least not easily...

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Grant Edwards                   grante             Yow!  I've been WRITING
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Grant Edwards

Remember doing that sort of thing often, as late 70's I was working for Digital and one of my jobs was running the PDP-11/70 for the engineering department. That division did all sorts of things from mimic displays[1] using colour graphics, to bit mapped graphics and even for UK Teletext inserters for the ITV network.

It was amazing how many terminals (even colour mimic display and graphic ones) were controlled from one system. At one time the Norwegian railway network ran off a dual system, not that I think the use of multiple processor networks in use today are any more efficient in MOST cases.

[1] Mimic display the (at that time normally) character based graphics for plant diagrams, railway networks, power grids etc...
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Paul Carpenter          | paul@pcserviceselectronics.co.uk
    PC Services
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Paul Carpenter

A little bit more history ...

AutoCAD started life as a package called InterAct which ran on a Marinchip Systems S100 box with a TI TMS9900 CPU. I saw InterAct being demonstrated. I still have one of those boxes in an attic somewhere. Marinchip Systems was John Walker's company before he started Autodesk.

Stephen

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Reply to
Stephen Pelc

The reason I asked was, I had a beta version of a PCB cad package running on my 8080 S100 CP/M box way back when. It only supported one specific graphics card - from Cromemco I think - which I couldn't afford, so I tried to hack it to use ASCII graphics on my terminal. It sort of worked, but was not pretty.

Bob

Reply to
Bob Stephens

The first PCB CAD program that I used was written by a tiny company called Dasoft. I worked for Digital Microsystems and Dasoft was just down the hall. We used a Z80 & CP/M based machine that had a builtin VTsomthing display adapter. We burned special character eproms for the adapter that would show PCB pattern and trace characters when the 8th bit of the ascii code was set.

In other words, if the CAD program output an 80h, the screen might show a pad in that position. An

81h, might show a vertical line, etc, etc. This way, we actually had a usable (by the standards of those days) redraw rates. I can't remember how we could tell what side of the board we were working on, but it must have been something painful.
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Jim Stewart

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