Subject: Re: Building new S100 floppy system From: ard at p850ug1.demon.co.uk (Tony Duell) Date: Sun, 21 May 2006 19:49:55 +0100 (BST) To: cctalk at classiccmp.org > > All: > > > > I have several random parts I'm going to pull together to build > a "new" floppy system for my IMSAI. I have an SD Sales Versafloppy > controller card (which used the FD1771B controller) and several 5.25" floppy > drives (all soft sectored). The Versafloppy manual indicates that it will > work with a Shugart SA400/450. When I look up the specs on the SA400, it > indicates that the unformatted capacity is 109.6k and the formatted capacity > is 81k. I didn't read the entire manual but this look like SSSD specs.

The 1771 is a single density (FM) controller only.

> I of course don't have any floppy drives like this but I have > several original PC drives (TM-100 and others) and several 360k drives of > various types. > > The question is this: can I use these later drives on this > controller without problems? If there are problems, what might they be?

It's almost impossible to make a drive that will handle double density but not single density. So your '360K' drives will be fine in that respect.

There are likely to be 2 other differences : 1) The SA400 was, IIRC, a single-sided unit. Your 360K drives are double sided. The controller may well not support double-sided operation, and it may use the side select pin for something else (DS3 was one common use I think). You may need to do a little bit of modification in this area.

2) I think the SA400 was a 35 cylinder drive, '360K' drives are 40 cylinder. This shouldn't matter unless, for some unknown reason, the controller only sends 35 step pulses when it tries to restore to cylinder 0. AFAIK any standard use of the 1771 won't suffer from this.