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Intel MDS888 Computer

Intel Intellec MDS800 MDS888 Development System 1977

Last updated: 11 Jan 2018

Roger Arrick MDS800 MDS888 Computer
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I worked on MDS systems in the 70s and purchased one on ebay. The system came from a company in Ridgecrest California named Hill Electronics.

My goal is to bring this system back to life, preserve it, and do some documenting to help others.

Thanks to all retro-computerists out there who are providing assistances and resources.

Technically my system is an MDS888 but it appears to just be the same as an MDS800.

My email is ROGER at ROGERARRICK dot COM

See the OSIRIS Operating System Archive page.
See How to run Kermit transfer program on ISIS/OSIRIS.
See Ken Burgett's story, creator of ISIS Operating system.

Personal Back Story

From 1977-1980 I worked with Intel MDS800 development system computers at Noakes Data Communications in Irving Texas. I was 16. We used them to design an 8080-based industrial computer which we manufactured for Shell Oil and some other companies. We had the 8080 In-circuit-emulators and the PROM programmer also. On my own time, I used the MDS800 to write a CP/M BIOS for our proprietary 8080 system which booted from 8" floppy drives.

In the mid-80s, the company went out of business and there was an auction which I attended. There sat 2 MDS800 systems with dual floppy drives, prom programmer and the ICE-80 modules. I bid against another guy and he eventually won. Later he came up to me and said "Hey, I just want the rack frames they're in, I'll sell you the computers". So I bought them, and we developed a good friendship. He was an airline pilot living in Hurst TX.

Life was hectic then with a family and small business and I never had the time to bring the systems back to life. Ultimately I sold or gave them away to a computer company in Louisiana. Later I was told they were put in a dumpster. :(

So, I'm very happy to get this machine and make it whole.


This ad from 1977 explains that an MDS888 is an enhanced version of the MDS800 with 64k RAM, more disk storage, CRT console, PLM and development support for 8085, 8048 and other processors.

Briefly: My MDS888 computer has dual-density floppy controller boards, 64k RAM, and a host controller for an external 20mb hard disk, dual 8" floppy drive box, UPP-101 PROM programmer, ICE80, ICE49.

◼ MDS-888 chassis 10/77 S/N:CP400 Label   Inside 18 multibus slots.
I haven't found the difference between an MDS-888 and MDS-800 yet.

◼ MDS-DDR Dual Floppy Drives 9/77 S/N:CR219 Label   Picture
Single-sided double-density (MMFM, not MFM) SBC202 system with dual Shugart 800-1 drives. and a Power-One CP155 power supply. Each drive has an adapter on its connector.

◼ Front panel board PWA 1000343-01E Picture  1702 ROM in slot #1

◼ CPU board PWA 1000340-01E Picture in slot #2

◼ 32K RAM board PWB460 1977 Picture in slot #3

◼ 32K RAM board PWB460 1977 Picture in slot #4

◼ Host board for Hard Disk 003-00003 Rev 4 from Data Technology Corp Picture in slot #5
This board connects to an external HD cabinet, see below.

◼ Custom wire-wrapped board with 8251 UART and serial port connector going to on back panel, in slot #11
Obviously just an additional serial port, possibly for high-speed communication with an external PC and moving programs.

◼ Floppy Disk Controller Channel board PWA 1000467-05M Picture in slot #16
This is an SBC202 Double-density single-sided (MMFM, not MFM) board.

◼ Floppy Disk Interface PWA 1001036-01A Picture in slot #17
This is an SBC202 Double-density single-sided (MMFM, not MFM) board.

◼ Monitor board PWA 1000351 (dual serial ports and ROM) Picture in slot #18

◼ General Purpose IO board PWA 1000929-01A not installed

◼ Hard Disk box #525 from Radio Switch Inc.
Power supply and ST-225 20mb HD. 50-pin cable to Host controller board in system.
Picture   Label   inside   Drive   Controller  

◼ 2 ICE-80 pods with boards and manuals.

◼ ICE-49 pod with boards and manuals

◼ UPP-101 PROM Programmer full of boards 8/77, and a cable and manuals. Picture   Label
4040 Controller, PWA 1000366-??
8748 personality module, PWA 1000735-01G
2708 personality module, PWA 1000967-02
2716 personality module, PWA 1000964-02

◼ Software - a single 8" ssdd diskette and some on the hard disk. I'm still working through this.


◼ Very first thing, lose screws. I turned this very heavy system in all different angles to fish out the screws floating around. Just one could totally destroy a system. One was from the front panel and one to the back panel.

◼ The system would not go into RUN mode, and produced no serial output. Traced the problem down to a bad 7474 on the Monitor board keeping the baud rate clock from going to the UARTs. Replaced it with a 74LS74. Now it boots and I can get into Monitor V2.0!!!

◼ The floppy drive box had a blown 3 amp slow-blow fuse.

◼ I noticed the filter cap for the 5v rail in the floppy drive box was oozing. A scope showed no ripple on the line but I replaced it anyway.

◼ The system didn't have a floppy drive cable. After looking at the drawing and seeing all the twisted pairs and 50-pin connectors, I figured out a phone PBX cable was pretty close, having the cabling I need and one of the connectors. Rewired the cable and soldered on a DC37 male which goes to the MDS888 back panel then to the floppy controller board. The system will now sometimes boot the diskette left in the system. Picture Pinout Large

◼ Did some research on the paint color of the MDS888 and figured out it was almost exactly the same as Sherwin Williams Polane-T Nitro Blue. This just happened to be the same blue that I had my paint vendor use on a product in the 90s. Got a few oz from him along with catalyst and did some touch up work. Perfect match.

◼ The foam on all of the air inlets was crumbling and making a mess. I finally found a replacement at Lowes. It's a filter used in window AC Units.

◼ The 2nd floppy drive had a bad 7428 which is a semi-unusual part - quad NOR gate with buffer outputs. A 74LS28 worked but I found some 7428 to use.

Hard Disk Subsystem

After seeing the internal Host controller and browsing the seller's other auctions, I concluded that the external hard drive system from Radio Switch probably went with this machine and bought it. Took my chances and it paid off. It does indeed go with the system and boots. See the Operation section for details.


◼ After the repairs, the system boots into MDS Monitor V2.0 !!!! It's very exciting to get this far. So much has to work at this point. I'd almost be happy with just this, but there is so much more that can be done.

◼ Sometimes the floppy diskette will boot into OSIRIS V 3.00. A DIR looks like this. What is OSIRIS?? My guess is a customized version of ISIS or something for use with the external hard disk.

◼ The 20m external hard disk boots into OSIRIS V3.00, does some reassigning of the drives then does a WDIR.
This reassignment sets the drives this way:
:F0: is HD partition #1 named SYSTEM.DSK See Directory page 1   Directory page 2
:F1: to HD partition #2 named APR86.LIB See Directory
:F4: is Floppy Drive 0 with floppy named OSIMAN.300 See Directory
:F5: is Floppy Drive 1 (mine doesn't work)

◼ Sometimes it won't boot and just gives an Error 24 with a Status 11 or Status 13. The ISIS book tells me this is a disk error. The book doesn't make clear what the status # means. I fear this means the Hard Disk is going bad. There is no ripple on the HD +5, +12 power supply. Once it gave me a "bad executive checksum" so I suppose that's either the HD or possibly memory.


See the OSIRIS Operating System Archive page.

Investigations by Jack M. suggests OSIRIS might be a short-lived version of ISIS designed for the last version of the MDS888 before the MDS225 development systems were introduced. Jack asked to see the contents of the ISIS.DES file, here it is copied to screen, it's binary, so many unprintable characters but there is some ASCII clues in there. My first attempt at using the putty terminal emulator to capture the file as a session failed but I'll work on that.

Jack offers this potentially relevant history:
The Egyptian Myth of Creation. From Geb, the sky god, and Nut, the earth goddess came four children: Osiris, Isis, Set and Nepthys. Osiris was the oldest and so became king of Egypt, and he married his sister Isis.

Jack suggests this is an important part of Intel history and I agree. My goal is to archive all of these files once I get the hardware going correctly. 'First do no harm' is my motto. Currently I'm not able to format and write a new floppy disk and definitely don't want to write on the HD. I've ordered an ST225 HD also for future backup but most of the HD can fit on a stack of floppies if I can get that going.

Intel PIII515 and other stuff

This batch of gear came with other things including an an ICE 5100 Emulator and a PIII515 80186 emulator. Here are some images:


And an Intel PGPIO board PWA 1000929-01A - Picture

Archiving Project

Very first project is to save the data on this floppy disk and hard disk. I know some of the hard disk is bad. There is likely a simpler way but first I tried the brute force method and used RealTerm with 8N1 parameters at 2400 baud to copy the DIR program to the console and capture it. The command is:


The captured file had an extra CR/LF at the beginning and 25 bytes of "COPIED :F0:DIR TO :CO:" CR LF "-" on the end which I deleted using this Hex Editor. Here is the binary of the DIR file (5747 bytes). Don't let the .txt extension confuse. So, it's a humble start. We'll see if anyone can load and run it.

Item's I'm Looking to Buy

I'm looking for a Single-Density floppy controller board set so I can read old disks I have including CP/M. The Intel SBC201 single-density board set is Channel board PWA 1000467 and Interface board PWA 1000603.

Also interested in another dual disk drive box - with or without drives.

The Zendex ZX-200A Floppy Controller board claims to emulate both SBC201 and SBC202 floppy systems so that's an option, as well as the ZX-208 which I've heard can also emulate them.

And the National Semiconductor BLC-8201 board is also said to be an SB201 replacement.

I'd also like to have an MDS-CRT since this system probably had one initially, and

MDS-770 printer.

MDS-PTR paper tape reader. Quit laughing.

Original printed documentation or diskettes for the MDS Development systems.

Intellec 4, Intellec 4/40, Intellec 8 computers.

Let me know if you run across these for sale or can offer any help.


MDS800 and ISIS resources by Bill Beech nj7p
Bitsavers MDS directories
Joe's MDS800 page
Computing History page
Vintage Intel page
Herb's Retro Technology info
Herb's M2FM disk format discussion


My email is ROGER at ROGERARRICK dot COM

Everything is Always Under Construction

Copyright © Roger Arrick