32 sector 8" floppies

From: Richard Erlacher <edick_at_idcomm.com>
Date: Fri Jul 30 12:03:35 1999

please see embedded remarks below.

-----Original Message-----
From: Marvin <marvin_at_rain.org>
To: Discussion re-collecting of classic computers
Date: Friday, July 30, 1999 9:14 AM
Subject: Re: 32 sector 8" floppies

>Richard Erlacher wrote:
>> It would be well to remember that, back when hard-sectoring was common,
>> was considered more efficient than soft-sectoring. Shugart 801 drives
>> certainly available with hard-sector support as an option.
>> did cost more, hence died off quickly enough.
>Why was hard-sectoring considered more efficient? IIRC, the soft sectored
>disks had more capacity than a comparable hard-sectored disk.

The overhead for soft-sectoring reduced the number of sectors per track from
32 to 26. This meant that you had (32 * 128 . . . 5 bits + 7 bits . . . 12
bits . . . must be 4K) 4K bytes per track. Anyway, 32 has most often been
more than 26 in my book. In some cases not much more, but more, anyway.
Drives could be jumpered to increase the sector capacity by skipping sector
holes. I was looking at the circuitry just yesterday (in the course of
troubleshooting an 8-inch drive) and recall that they allowd for 8 and 16
sectors per track as well, simply by dividing the sector pulses down.

This was probably less efficient, due to the decisions made along the way,
though it didn't have to be that way. The additional capacity didn't have
to be simply doubled just because the number of sectors was halved. I
recall something about 8 sectors yielding a capacity of somewhat more than
4K bytes. This does add up, since there are 83,333 nominal bit times per
revolution, half of which were used for clock, of course, if FM was the
modulation scheme. Since MFM was lurking on the horizon, I guess the LSI
makers just decided to forget about hard sectoring. Nobody believed anyone
would ever want a floppy diskette format which yielded more than what MFM
would offer. It's just like nobody once believed that more than 64Kbytes of
memory were desirable in a home computer, right?

The difficulty arises from the general discontinuance of the manufacture of
the FDC's capable of dealing with hard sectored media. Both NEC and Intel
made a version which handled hard sectored media back in '76. It
disappeared from their repertoire by '78, though. NEC also made a digital
tape cassette controller which went the same way.
Received on Fri Jul 30 1999 - 12:03:35 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:32:14 BST