[TUHS] 3330s, 3340s, Winchesters... (was: /dev/drum)

Paul Winalski paul.winalski at gmail.com
Thu Apr 26 06:54:16 AEST 2018

On 4/24/18, Greg 'groggy' Lehey <grog at lemis.com> wrote:
> Hmm.  The earliest 3330s had 100 MB per disk, considerably more than
> the 3340.  I had thought that the 3340 had fewer surfaces.  And the
> 3330s definitely only had one disk per unit, though they brought out
> an 8-drive cabinet with a whopping 2.4 GB (by the time I used them).

The 3340 indeed had fewer platters per unit than the 3330, and because
of that a lower disk capacity.  Both the 3330 and 3340 were CKD
format, not fixed-block, so the capacity depended on the record size.
Highest storage capacity was achieved with one record with a
zero-length key field covering the full track (called full-track

According to the IBM Archives web page
the 3330 was code-named Merlin.  It could have from 2 to 16 spindles
per controller.  Originally each disk pack had a maximum capacity of
100 MB.  The 3330 model 11 used IBM 3336 disk packs that had double
the original capacity (up to 200 MB).

This IBM Archives web page
says that the 3340 was code-named Winchester.  This page reports, but
does not verify, the "30-30" Winchester rifle story.  The IBM 3348
Data Module, the disk pack equivalent for the 3340, was a sealed
module that contained the head assembly.  This reduced the hazards of
head misalignment and surface contamination.  Unlike later
sealed-module disks, the 3348s were removable media.  Modules with
maximum capacities of 35 MB or 70 MB were available.  There was also a
70 MB module with up to 0.5 MB accessible from fixed heads.

-Paul W.

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