3.5" floppy disk revisited on the UNIX pc ...

[Lenny Tropiano]

Yes, Gil and I have done it again ... another ribbon cable coming out
of our machines.  (That's four cables for me, two 34 pin cables, one
20 pin cable, and a 36 pin cable for my parallel printer).  It's getting
a little crowded back there :-)

After coming back from the Trenton Computer Festival last weekend, both
with 720K 3.5" floppy disk drives (for $30 a piece), we decided to install 
them in our UNIX pc's.  The drives are Sony Model MP-F63W-01D, 3.5" 720K
floppy units.  We bought them, the cases, the ribbon cable, the switch,
edge connectors and the DIL connector all for about $60/each... 

The only "snag" we had was that the drive didn't assert the FDREADY* signal
on pin 34.  This caused the system to think there was no disk inserted, or
the door was open, even though neither were true.  Gil whipped up a little
fix for that one and he grounded the FDREADY* signal only when the drive
was selected. 

Now how did we manage to get both drives on the UNIX pc at once, since the
hardware only supports one ...  Well it's sorta a hack, but basically it's
a mechanical switch (SPDT) that switches the FDRIVE0* signal (pin 10) between
the 5.25" drive (360K) and the 3.5" drive (720K).  Both cannot be accessed
at the same time, but who cares ... the switch in one direction gets you
original 5.25" drive that is still in the case, the other way is the 720K
drive externally...

It's nice to have all this space on a floppy!  

/floppy   (/dev/fp021):     1560 blocks     190 i-nodes
                 total:     1590 blocks     192 i-nodes

(That's 814,080 bytes ... 10 sectors/track, 80 tracks)... 800K!

I was able to put a floppy boot unix, floppy filesystem (all the necessary
patching utilities [fsck, fsdb, etc..]) and the diagnostic program all
on a 3.5" disk with a verbose loader.  Ahh, no more switching disks to
boot a Floppy Unix!

If you want more details on the hardware aspects, I suggest you contact
my hardware expert... Gil Kloepfer, Jr. (gil at limbic) 

						-Lenny
-- 
Lenny Tropiano             ICUS Software Systems         [w] +1 (516) 582-5525
lenny at icus.islp.ny.us      Telex; 154232428 ICUS         [h] +1 (516) 968-8576
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        ICUS Software Systems -- PO Box 1; Islip Terrace, NY  11752