Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!rutgers!ames!amdahl!dlb!sun!cmcmanis
From: cmcmanis@sun.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: Disk speeds on Atari ST and Macintosh
Message-ID: <12753@sun.uucp>
Date: Thu, 5-Feb-87 12:23:49 EST
Article-I.D.: sun.12753
Posted: Thu Feb  5 12:23:49 1987
Date-Received: Sat, 7-Feb-87 15:35:33 EST
References: <8701290450.AA16048@cory.Berkeley.EDU> <756@tekfdi.TEK.COM>
Organization: Sun Microsystems, Inc. - Mtn View, CA
Lines: 42
Keywords: disk speed I/O interleave transfer formatter
Summary: Not if you use a WD controller

In article <756@tekfdi.TEK.COM>, mhorne@tekfdi.TEK.COM (Mike Horne) writes:
< I (unfortunately) haven't had the opportunity to finish writing a
< program to do my own formatting, but the concept is simple.  The floppy
< controller can do a 'track write' which is used to format a complete
< track with a sector layout.  One would only need layout a typical track
< in memory (with all of the necessary inter-rec gaps, etc., in place),
< tell DMA where the buffer is, then give a 'track write' command to the
< floppy controller.  That is all the TOS routine is doing, but you could
< play around with the inter-record spacing, interleave, etc.  You could
< easily get 10 sectors on a track, and possible 11 if you get rid of
< a large chunk of the end-of-track gap, though you get closer and closer
< to losing your data in the bit-pit if there isn't enough gap (e.g. when
< writing to the last sector on the track, you could wipe out the first
< sector, the start of track mark, etc.).
< 
< By the way, all of this stuff (including the necessary track layout)
< can be found in ST Internals, most of which you will have to get from
< the BIOS listing (flpfmt()).  It isn't difficult to understand or decode.
< 
<  Michael Horne - KA7AXD             FDI group, Tektronix, Incorporated

[I have heard the ST uses the WD controller for floppies if this is not
 true ignore this]

As Mike indicates doing a track write is the standard way to format
a floppy controlled by a West. Digital controller. There are some
"magic cookie" bytes that are in the track data that get translated
into header bytes and sector crcs and the like. And you can play around
with the gap's however you will not be able to get reliable operation
with 10 or 11 sectors. The gaps protect the data in subsequent sectors.
When a sector is written the last thing the disk does is write the 
sector crc, the write heads are then switched "off". If the gap is 
too short they aren't off before they pass over the address mark of
the next sector and they change it. Poof! Unreadable sector. It is
fun to play with, I wrote a program to do so when I wrote a CP/M 
bios for WD controller. You end up learning a whole lot about the 
mechanics of a disk drive, and the timing constraints. 

-- 
--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.