PerSci 277 floppy drives

Barry Watzman Watzman at
Tue Mar 15 18:22:02 CST 2005

I have quite a bit of experience with these (and, by the way, I'm looking
for one or two ....).

The Persci drives for the most part are single full-size drives that accept
two different media in the same drive.  They are not quite the same thing as
"dual drives" because there is only one head positioner for both drives.
However, it's a huge voice coil and it's very fast (1 millisecond per

The drives have a horrendous number of very, very different configuration
achieved by about 4 dozen jumpers.  There are several dozen "standard"
configurations, and many of them are quite non-interchangeable.

The interface is a standard 8" floppy interface (50-pin connector), and they
can be used with most controllers ***IF*** they are properly

However, some of their quirks are very, very unique.  One is the single
positioner, moving the head of the "A:" drive also moves the head of the
"B:" drive, and vice-versa.  This requires a different BIOS for Persci
drives vs. a more conventional configuration of two separate drives.

Another thing is seek timing.  The seek speed is very, very fast, and the
servo system is capable of dynamic acceleration and deceleration.  To use
this, which is all but mandatory, instead of sending step pulses at, say, 6
nSec. per pulse (track), the step pulses are sent at a VERY high rate, over
100,000 pulses per second.  The drive buffers them, and dynamically
accelerates the head to max speed for the seek, and dynamically decelerates
it at the end of the seek.  There is a new interface signal "seek complete"
to tell you when the head has arrived at the desired track.  This is totally
different than a normal stepper motor drive, and requires both some minor
hardware changes (which are supported by almost all LSI-based S-100
controllers, e.g. Western Digital) and some software changes.  It's not
difficult and it works well, BUT it means that a BIOS for a conventional
stepper motor drive and a Persci drive are two separate BIOS'.

These drives are a wonder to behold, the main board is huge (something like
200 square inches) and beautiful.  But they are almost unserviceable, since
parts are not available and they used some very unique components, and also
they are quite fragile (there is a special insert required for shipment, and
they are unlikely to survive shipment without that insert).

I personally scanned all of the Persci service data on the 270/277 drives
and they are up on Howard's site for download, so at least documentation is
available.  If you have any questions, I'll try to help, but if they are
"dead" or grossly non-functional, the chances of resurrecting them are slim.

More information about the cctalk mailing list