origins of IBM 3740 diskette format

From: mhscc_at_canada.com <(mhscc_at_canada.com)>
Date: Thu Feb 24 21:47:55 2005

----------Original Message:
> Date: Thu, 24 Feb 2005 21:12:51 +0100
> From: "Nico de Jong" <nico_at_FARUMDATA.DK>

> Subject: Re: origins of IBM 3740 diskette format
> 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

Errr, ummm...
73x26x128=242944
80x2000=160000
Am I missing something?

FWIW, from the 1984/5 Computer Cookbook (p.82):

"Finally, in the early 1970s, IBM sponsored a competition among
several research teams to design a replacement to its infamous
card punches.
...
IBM's 3740 data entry station put its stamp of approval on the
floppy. The 3740 format is still the de facto interchange medium
within the industry.
...
IBM's design for the 3740 was very conservative. At the time, IBM
believed that floppies would be used for the batch entry of data.
The full-sized floppy was designed to hold the same amount of
information that 3,000 punch cards would hold - the maximum of
what a single keypunch operator could do in a day.

mike
Received on Thu Feb 24 2005 - 21:47:55 GMT