Pinout for SED9421

[Tim Shoppa]

Allison <ajp166 at bellatlantic.net> wrote:

> >
> >Subject: Pinout for SED9421
> >   From: lee davison <leeedavison at yahoo.co.uk>
> >   Date: Sat, 26 Nov 2005 02:50:31 +0000 (GMT)
> >     To: cctalk <cctalk at classiccmp.org>
> >
> >> Figures..  However they loose a full sector for every four
> >> which is pretty bad considering sync and other overhead that
> >> floppies incur.
> >
> >It's not that clever. One 2K block of data per track, no sectors,
> >no sync, just the 125Kb/s async bitstream. Wait for the index
> >pulse and read/write the whole track. At the time it was a lot
> >cheaper than any other disk controller.
> >
> >Lee.
>
> They trade being efficient for a lot. Across 35 tracks (sa400) thats
> about 18k.   NS* hard sector was 10x256 (2560bytes) track, and a 
> sync chip (one sector per track) will give that much maybe more 
> as well. 
>
> I think what they did was very clever and dirt cheap and the hidden feature
> of async is the extra two bit times allows a bit more time to read/write the
> port 80uS vs 64uS typical. 
>
> Wacky, but soon as you said OSI.. ;)  they were a creative lot.
>
>
> Allison

Allison -
  You forget (or maybe have repressed) how sucky the Ohio Scientific
file system was. When every file you create must be explicitly specified
by which tracks it resides on, you don't notice little things like a bit
lower capacity!

Tim.