origins of IBM 3740 diskette format

From: Paul Koning <>
Date: Thu Feb 24 13:46:29 2005

>>>>> "Tom" == Tom Jennings <> writes:

 Tom> 8" floppy: 77 tracks, 26 sectors/track= 2002 sectors 128-byte
 Tom> sector payload

 Tom> IBM punched card= 80 characters

Unless it's a System 1 96-column card...

 Tom> Isn't there some standard unit of IBM cards ("a box") that's
 Tom> 2000 cards? My friend David says this is the reason for the
 Tom> format. He had some facts to back it up but that's now vapor in
 Tom> one ear (I think it went out the other but I can't remember).

Unclear. A box may be 2000 cards, I could believe that. But if the
3740 format were inspired by boxes of cards, it would have an 80 byte
sector size. That certainly would fit IBM practice, after all they
had disk drives where the sector size would vary from sector to sector
even on a single track, and people often created files with 80 byte
sectors since they were card images...

Hey, that suggests a fun topic: oddball sector sizes.

"Normal" sector sizes would include the obvious 512 bytes, and also
128 bytes for floppies.

Uncommon ones? Well how about these:

IBM mainframe drives: anything you want up to a track or so.
IBM 1311: 200 digits (6-bit signed BCD).
CDC 6000 series: 322 12-bit words.
DEC RS64: 64 bytes.
DEC RF11: 2 bytes.
DECtape, PDP-8 format: 129 12-bit words.

Received on Thu Feb 24 2005 - 13:46:29 GMT

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