The original 23FD drive as used in the 3830 control unit for 3330 DASD
was a read only device and I remember one of the large system CEs
showing me the diskettes for them, the sleeve was much stiffer than
later diskettes.
The read/write 33FD was first shipped in 1973 and when I started at IBM
in 1979 several of the terminal controllers started up from one of
them. The head carriage was moved by a crude stepper that turned 90
degrees per step and was coupled to the bottom of a lead screw by a
Geneva drive. The drives did not have a track zero sensor so when
initialize they would take about 80 down steps. There where collars
fixed on the lead screw that limited the travel and the one at the
bottom would hit a plastic tip on the head carriage to stop the head at
track zero, and when being initialized would hammer on the down stop
several times especially if the head was already close to track zero.
In my early days as a CE I was thrown into fixing a S/34 that I knew
nothing about but it turned out to be a problem with the 33FD diskette
drive that I was familiar with from working on terminal controllers, the
down stop had broken off the head carriage. I was at a remote location
and had no parts, but was able to fix the S/34 by swapping its drive
with one from a 3742 the customer was returning to IBM. Before I left
field service the first time in 1983 double sided drives where already
starting to appear, these drives had a proper stepper motor and a taught
band to move the head carriage, but still did not have a track zero sensor.
Several years later I was a hardware support person in the Toronto Lab
and one of the rooms I looked after had a 3880 controller with a couple
3380 DASD units and the first time I heard the 3880 start up I thought I
know that sound, so I looked inside and sure enough it IMLed from a 33FD.
Paul.
On 2026-06-08 22:46, William Donzelli via cctalk wrote:
There is one in the 3830 control unit as well. This large box
controlled the DASDs (disks) on early S/370s. I have one, and it still
works.
--
Will
On Mon, Jun 8, 2026 at 8:41 PM [email protected] steven--- via
cctalk <[email protected]> wrote:
On 06/09/2026 9:30 AM AEST Murray McCullough via cctalk <[email protected]>
wrote:
54 years ago the 8 inch floppy came into existence. It can be said it
helped to make micr-computing possible.
Happy computing.
Murray 🙂
The IBM System 370/145 announced September 1970 and shipping June 1971 had a
23FD drive for microcode loading, IIR it was on the front panel at the top left
or maybe in the CE area inside on the side, not sure exactly now. When I was
doing work experience at IBM at the end of high school there was a Model 145 in
a warehouse waiting to be scrapped and I recall looking at the 23FD in it then.
