origins of IBM 3740 diskette format

From: Nico de Jong <nico_at_FARUMDATA.DK>
Date: Fri Feb 25 00:12:41 2005

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

Yes. The discussion is not about bytes, but about card images.
A card image (apart from some special ones like 96 bytes and "stubs" of
about 30 bytes) is 80 bytes. Furthermore, the lowest sectorsize that could
be formatted on a 3740, was 128 bytes. As there are 73 "user adressable"
tracks with each 26 sectors, there are only 1898 sectors. And as the
discussion is about card images, there is only room for 1898 cards, unless a
technique called spanning is used.

> 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.
This is worth a whole new topic, as I happen to know a bit about that (I'm
running a service bureau for media conversion)

> ...
> 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.
That is correct; the 3740 family came to be rather big, eventually ending up
with the 3749(?) data entry station, where one could use DSDD floppies with
a sector length of 1024. IIRC, it could accommodate 6 segments per track,
ending up with 8 x 1024 x 73 x 2 = 1.1196.032 bytes

> 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.
See discussion on "spanning"

Received on Fri Feb 25 2005 - 00:12:41 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:37:40 BST