| Posted By
someone
on 2002-11-23
|  How to use the 1551 "%S" command?
AFAIK the 1551 DOS command "%S" can be used to determine the sector interleave for writing files. But how is the syntax for that command? I have tested OPEN 1,8,15,"%S"+CHR$(N) with N=several values (for example 0 or 1 or 10). Neither the write nor the read accesses were accelerated.
In my opinion this command should influence those speeds, because if the desired sector just rushed by under the head the controller has to wait another disk rotation. On the other hand, if the needed sector is available immediately after the controller starts to wait for it the overall transmission speed should be a bit faster.
Does anyone have some experience with this topic?
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Posted By
SVS
on 2002-11-23
 | To have good results by %S,
you have to calculate the optimizing interleave value. This depends by the rotation speed of your drive motor and *could* be set with a screwdriver.
When for example you set an higher speed, you could have as optimized interleave: 7.
After this you have to run the command to set 7 as DOS parameter.
Only now you can write a file. When reading it you finally should obtain a speed increase 
These operations are a bit dangerous because, as I experienced, you have very little range to modify motor speed, without affect the working of fastloads.
Then: do your tests on a spare-disk! 
P.S. Who is "someone"? 0
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Posted By
someone
on 2002-11-23
| Do you mean
"7" as an ASCII seven ($37) or a binary seven ($07)?
P.S. Who is "someone"?
Well, it's me - just... someone.
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Posted By
SVS
on 2002-11-23
| I guess "7" as ASCII, as for other
direct commands (%R...).
The standard interleave is 8 for 1551, or for 1541+GEOS, it is 10 for 1541.
Good luck.
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Posted By
SVS
on 2002-11-23
| Oooopps! Correction...
I've just checked the 1551 manual and I found that the datum inside the command "&S" must be supplied as binary, that is CHR$(nnn) where nnn is normally 8).
Sorry for my previous mistake :#
P.S. The same is for %R and %9 commands.
Bye.
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Posted By
someone
on 2002-11-23
| Thanks!
I'll check this out...
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