12 Jan
1999
12 Jan
'99
11 a.m.
On Tue, 12 Jan 1999, Doug Yowza wrote:
When going to the directory on a system without a track 0 stop or track
0 switch, it DOES substantially reduce the average access.
But, if there IS a track 0 stop, or track 0 switch, then it is normally
possible to get to track 0 at full maximum velocity, rather than stepping
one track at a time, pausing (and maybe reading) before taking the next step.
That usually makes even the maximum seek to track 0 take even less than
half the time that track by track stepping would.
AND, on systems with a track 0 switch, track 0 is the one place where you
always know where you are. Therefore, whenever there is an unknown or a
seek error, the system will normally send the head out to track 0 and
count back in again.
--
Fred Cisin cisin(a)xenosoft.com
XenoSoft http://www.xenosoft.com
2210 Sixth St. (510) 644-9366
Berkeley, CA 94710-2219
Microsoft
produced some "Stand-Alone BASIC" systems. They had file IO,
and used a a directory structure that was, in principle, similar to that
of MS-DOS, although they subscribed to the seek center fallacy of putting
the directory on a track approximately halfway towards the center.
Remind me again
about why this was a fallacy. I thought the idea was to
reduce the average seek time slightly by minimizing the average distance
the head traveled by factor of 2 versus a directory on a track at one end
of the disk.