origins of IBM 3740 diskette format

[Nico de Jong]

From: "Tom Jennings" <tomj at wps.com>
Subject: origins of IBM 3740 diskette format


> 8" floppy:
> 77 tracks, 26 sectors/track= 2002 sectors
> 128-byte sector payload
>
> IBM punched card= 80 characters
>
> Isn't there some standard unit of IBM cards ("a box") that's 2000
> cards? My friend David says this is the reason for the format.

The way I see it, it is rubbish. Unless my brain has turned to jelly, there
were only 73 useable tracks, as the last ones were reserved by ERMAP =
reallocations of defective tracks. Track 0 was used for VOL and HDR labels.
The ERMAP was located at sector 5, IIRC. The 2000 itself is right, but there
are only 1898 sectors on a single side singe density 3740 diskette (73 x
26). So, unless you did some fancy things like "spanning" ( a term used for
having parts of a record in different sectors), there was no way you could
get a full box of cards on a single (single sided) floppy.

Nico