🚀 go-pugleaf

In article <967@batcomputer.tn.cornell.edu> braner@tcgould.tn.cornell.edu.UUCP (braner) writes:
>[]
>
>Format+ (the "dead sector" speed-up scheme - I use only 80 tracks, though)
>seems to read a bit faster than Twister.  It does not speed writing. (Does
>Twister?  Without turning verify off?)  My only complaint is that I have no
>idea how it works...
>

My understanding is as follows:

TOS doesn't know how many sectors are on a track, despite the information
being present in the boot sector. It move to the next track when it gets
an error looking for a sector. The 1772 searches three revolutions of a
disk before deeming a sector "not found" and returning an error. So, when
TOS is looking for sector n+1, where there are n sectors per track, it
takes three revolutions of the disk to get the error, and move to sector
1 of the next track. Format+ writes a bad sector ID for sector n+1 on
each track, so TOS sees the error in one revolution instead of three,
resulting in faster I/O. 

TOS also checks after a step/seek to see if it got to the right track
by reading the first address mark it can find. Unfortunately, the
combination of step/settle/read-address causes sector one on the destination
track to be missed, and another revolution to be wasted.

TWISTER compensates for the track step/head settle/position verify
time by staggering the sectors on the tracks in relation to the index mark,
like this:

  INDEX---+  Sectors
(TRK 00)  !  1  2  3  4  5  6  7  8  9  10
(TRK 01)  !  3  4  5  6  7  8  9 10  1  2
(TRK 02)  !  5  6  7  8  9 10  1  2  3  4

NOTE!!! Twister does put TEN sectors on a track, which is the cause of
a lot of the problems copying things to "TWISTED" disks in any manner other
than file by file. (Standard TOS disks have nine sectors). In double sided
disks, the stagger is applied to each side, as well as each track.

So, the best performance is probably a combination of the stagger of
"TWISTER" and the bad address mark of "FORMAT+". Also nice would be options
for nine or ten sectors per track, 80, 81, or 82 tracks. Since "TWISTER"
is copyrighted, everything would have to be re-written from scratch. I'm
working on it, and should have it in a couple more weeks (he said hopefully).
Yes, I will be posting it when I have it done.

GENERIC WARNING - We are dealing with a collection of random data here,
and any/all of it could be wrong. This is just the way I have come to
understand the different techniques being used. My format program isn't
working yet, so I can't test these things enough to see what really
does impact the performance.