View Full Version : Shugart 900-1 Floppy Drive

Kevin Williams
November 9th, 2017, 05:24 PM
Hi Everyone,

I know this is not specifically an S100 question, but it is 8" floppy related so I was hoping this would be the best place. I recently picked up what I thought were 4 Shugart SA-801 Floppy drives, but it turns out I have two labeled 900-1. The primary difference I can see is that instead of a .1" 50-pin connector, it has a honking .156" 50-pin connector. It's still as single sided drive, and has a white bezel just like the 801's. I suspect it was an OEM drive, but I can't find any info on what it may belong to. It's a pain, as I will need to build a weird adaptor to test it, after I spend some time making sure it's wired the same. Truly odd beast.

Thanks everyone!

November 9th, 2017, 05:48 PM
From Computerworld June 18, 1975:

Shugart Associates will supply National Semiconductor with its SA900 flexible disk drives for use in National’s floppy disk operating system for its IMP-16 microprocessor prototyping system.

I can't find anything showing the IMP-16 floppy connector though so I can't verify that it matches the one on your drives.

Kevin Williams
November 9th, 2017, 05:54 PM
Hey, thanks so much. I should have searched the archive. It's odd how little 8" floppy info there really is. BTW, it's a 44 pin, not a 50 pin connector. I made an assumption, then I actually counted them. :-)

I'll dig in more and see what I can find, thanks again!

November 9th, 2017, 06:02 PM
Sorry, but the SA-900 is a doorstop unless it's a really late one which used some of the same parts as the SA-800s which came with the LSI logic board, OR you have a computer that they were designed for.

The SA-900 uses a different interface with a 40-pin edge connector, and is not compatible with the standard 50-pin edge connector of the SA-800, SA-850, SA-810, SA-860, etc...

On the really late replacement SA-900 drives, I think the motors, and the head assemblies may be used on a SA-800 type drive.

All of the SA-900 drives I've ever come across had the non-rackmount tyoe chassis, so they don't fit in standard 8" drive enclosures which were designed to fit rackmount drive chassis which can be mounted horizontally side by side in a 19" industrial rack. The SA-900 and SA-800 drives that came on non-rackmount chassis are too wide to be mount is a standard rack side by side horizontally..

Kevin Williams
November 9th, 2017, 06:17 PM
Ok, it makes sense, and I understand now what the white bezels are for. All four of the drives I have appear to be industrial rack-style drives, even the SA-801's. Looking a little more closely, I believe I see what they were trying to do. The normal power connector is missing, and is wired to the connector. They used bigger pins to accommodate the power, and eliminate the connector. You still have to power the motor though, so not sure what the advantage is.

Do you happen to know if the specs are the same? IE, is it still a 360rpm, 77 track, double-density drive? I think I might be able to figure out what's what from the schematic of the 800, or is it just a waste of time?


November 9th, 2017, 07:11 PM
No, I think you can work out cable connections for the 900. Here's the service manual that includes schematics (http://bitsavers.informatik.uni-stuttgart.de/pdf/shugart/SA900/50614-2_SA900_Service_Aug77.pdf).

This reminds me of the old Calcomp floppy drives in that DC power is supplied on the same connector as the logic signals.

Dwight Elvey
November 10th, 2017, 09:34 AM
My Nicolet 1080 has what I think is a SA-915 but could be a SA900. What is unusual is that it has a 50 pin SA connector and a small adapter board to connect to the 40 pin connector. I didn't study the 50 pin cable close enough to state that it would be signal compatible with the SA800 series drives but I don't recall seeing anything that would indicate otherwise. My guess is that the cable and controller were designed for the SA800 and they got an especially good deal on the SA900 series. The rate of rotation is the same as the SA800 and I always assumed they were basically the same. It is a single sided single density drive.
As I recall, it has the SA900 3 transistor stepper drive and not the SA901.