Another rare beast...

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jonb
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Another rare beast...

Post by jonb » Wed Oct 03, 2018 4:48 pm

Dear friends

I would like to introduce you to the latest beast to join my retro computing menagerie.
IMG_4940.jpg
Blue, very blue
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Screen has some fungus..
IMG_4942.jpg
Battle scars
IMG_4944.jpg
More battle scars
IMG_4945.jpg
Rear panel
IMG_4946.jpg
Serial heaven

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leenew
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Re: Another rare beast...

Post by leenew » Wed Oct 03, 2018 4:53 pm

Yowsa! What is it? And what year would it have been built??

Lee.

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jonb
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Re: Another rare beast...

Post by jonb » Wed Oct 03, 2018 5:15 pm

It's an Intel MDS computer. Not sure the year of manufacture, but it looks like July 1978. There's a label on the back with the serial number, model and "7/78" stamped on it. Some of the ICs have date codes in 1974..

This is the MDS-231 variant, without the external twin 8" floppy drive bay and it's missing the drive controller that operates the external drives, too. This is no big deal as the external drives used a weird M2FM encoding that very few machines can read or write, so boot disk provisioning would have been a difficult proposition. Instead, it has the integrated controller, a single density thing which will limit how much I can get on an disk. Speaking of which, the case has a drive bay (covered) and I've got a spare 8" Shugart to put in there when I'm ready. For now, I will try an HxC floppy emulator and a 50-34 way floppy adapter card (just a wiring exercise really, it's got no clever logic on board) which is currently plugged into my TRS-80 Model II.

These machines were originally sold by Intel to help manufacturers build systems using Intel chips. As such they were industrial in nature, rugged, heavy and came with reams of documentation, a big fat monitor on EPROM, a disk based operating system called ISIS-II and a catalogue full of add-ons such as an EPROM burner and various CPU emulator modules. It has a PL/M development environment. It can run CP/M as it's got an 8080 at its heart (though you could buy any number of other processor cards for it) and it uses the Multibus back plane (closely related to S100, apparently, although the connectors look entirely different).

An exotic piece of computing ephemera, then, so why is it interesting (to me)? Well, it's the cousin of the MDS-800, a machine that Gary Kildall used to write CP/M on (including the utilities PIP, ASM, ED etc, which were written in PL/M). Indeed, the main CP/M distribution disks feature a BIOS for the MDS. So, as I am a CP/M admirer, and as this machine is in need of restoration, I took it under my wing, so as to speak, with the intention of bringing it back to life. It is, I think it is quite rare (although I just looked on a certain auction site and found a lesser MDS-231 sold for 1 EUR + 400 EUR P&P).

Besides, it really looks cool in blue. I mean come on, who doesn't want a blue computer?

:D
Last edited by jonb on Wed Oct 03, 2018 5:23 pm, edited 1 time in total.

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Re: Another rare beast...

Post by jonb » Wed Oct 03, 2018 5:20 pm

So far I have checked out the PSU, a bloody great beast of a thing, and found it (mostly OK). Certainly, the rails I need to operate the CPU and I/O boards are present and I could even power the screen up. I've put the thing together in a sort of minimal configuration, hoping to be able to operate it via the TTY serial port (which its monitor allows).

So:-


IMG_4937.jpg
IMG_4938.jpg
IMG_4939.jpg


But... dare I press that big white power switch? What magic smoke awaits?
Last edited by jonb on Wed Oct 03, 2018 5:21 pm, edited 4 times in total.

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hoglet
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Re: Another rare beast...

Post by hoglet » Wed Oct 03, 2018 5:49 pm

Is it 8080 based?

If so, make very sure the +5V, -5V and +12V supplies are working, otherwise you'll toast the 8080.

Maybe also check for shorts (to ground) on those three rails with a meter before applying power.

Dave

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Re: Another rare beast...

Post by Coeus » Fri Oct 05, 2018 11:59 am

I do remember doing something om one of those back in about 1985. Having been used to the BBC Micro it seemed a bit of a relic, even then.

If this machine came with an OS in the form of ISIS II and even has a PL/M compiler (written under contract by Gary Kildall, the CP/M chap AFAIK), why was CP/M required and why did it take off in a way that ISIS II did not? What ISIS II too cumbersome to use? Were Intel too greedy about licensing it? The latter would seem strange when they appear to have produced this system, including the compiler, specifically to encourage uptake of their microprocessors. Maybe they were just expecting them all to go into embedded applications and failed to foresee the emergence of general purpose computing based on the microprocessor.
Last edited by Coeus on Fri Oct 05, 2018 11:59 am, edited 1 time in total.

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jonb
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Re: Another rare beast...

Post by jonb » Fri Oct 05, 2018 12:43 pm

Nah, I think Kildall had this great idea for a general purpose operating system that could run on any 8080 machine given a few simple prerequisites, then he implemented it on the MDS-800 and founded DRI.

There had been operating systems like it before, of course, but I think the key feature of CP/M is the BIOS and its standard vector table. That's why they called it "The Software Bus". All you had to do was implement a simple BIOS and your new computer could run it.

Kind of like DOS. Wonder where they got that idea from?

(BTW, I read the key feature of DOS was the FAT. Apart from that it was a rip of CP/M.)

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