Date   : Fri, 22 Feb 1991 08:25:36 GMT
From   : pilchuck!dataio!fnx!del@uunet.uu.net (Dag Erik Lindberg)
Subject: Using 3.5" floppies instead of 8" floppies

In article <11375@uhccux.uhcc.Hawaii.Edu> ralph@uhheph.phys.hawaii.edu
(Ralph Becker-Szendy) writes:
-Since someone asked what the method is to hook up a 3.5" floppy disk drive
-instead of an 8" drive, here is a listing of pin-numbers on the cables.
A 5.25"
-HD or 3.5" HD floppy is electrically nearly equivalent to a 8" DD floppy. The
               .......
-
-If the 5.25" or 3.5" drive really needs the MOTOR ON signal (most newer ones
-can be jumpered to do the motor control themselves), just strap it to ground,
-that keeps the engines under full steam.

**** DON'T DO THIS !!!! ****
Most newer 5/25" or 3/5" drives do not onload the head when the drive is not
being access.  If you leave the drive running continuously, you will wear
out the diskette at an alarming rate.  I have several souvenier diskettes
where nearly all the magnetic oxide has been worn off the diskette from
being left in drives that were running continuously.  You could practically
read a newspaper through one of them.

If you can't do it properly with a real motor control, then either a) tie
motor-on to the drive-select and always delay 1/2 second after selecting
before accessing drive, or b) build a small timer that will pull down the
motor on line for 20-60 seconds after a select.

-Some 8" disk drives can have very elaborate selection schemes (binary select,
-where SELECT 0 is a global select and SELECT 1-3 are a 3-bit drive address),
or
-they use weird combinations of select lines instead of SIDE SELECT to switch
-between the two sides. If one really >has< to emulate such madness, a few TTL
-gates might be required.

Or a single PAL device.

-One more weirdness: 3.5" drives usually have non-removable terminators in the
-kOhm range, instead of the good old ~200 Ohm removable terminators. I have
-never tried using just a 3.5" drive at the end of a long flat cable with no
-other termination, and it probably is a real bad idea since reflections
must be
-fierce.

I've had no trouble with 6 foot cables.

-I never understood why people would want to replace 8" drives. They are
-friendly, solid, reliable, and teach respect for computers. I have lost a 3.5"
-disk drive in the pile of stuffs on my desk; that could never happen to an 8"
-drive. Installing a 2-drive set with power supply is very good exercise and
-builds character and muscles. They heat the office, and provide a pleasant
-acoustic background (I call mine the "afterburner"). You will never forget
a 8"

Computers and human beings should not share the same room when either is
in operation. :-)

-- 
del AKA Erik Lindberg                             uunet!pilchuck!fnx!del
                          Who is John Galt?