Message-ID: <258@nmtvax.UUCP>
Date: Thu, 7-Feb-85 16:02:26 EST
Article-I.D.: nmtvax.258
Posted: Thu Feb  7 16:02:26 1985
Date-Received: Tue, 12-Feb-85 04:46:51 EST
References: <126@nvuxd.UUCP> <>
Reply-To: djm@nmtvax.UUCP (Dieter Muller)
Organization: New Mexico Tech, Socorro
Lines: 28
Keywords: Track/Sector Lists
Summary: 



I discovered a neat little bug in DOS last night.  Playing with a disk
that had been munged a long while back (never had the time to fix it,
it was only a game), I would be bouncing along (the game was Eamon)
happily until, for no apparent reason, the head would start doing read
seeks to two different sectors as fast as it could.  Looked like a
classic example of pointer A -> pointer B -> pointer A.

Since this was the problem with the disk previously (as I belatedly
remembered), I grabbed a disk dump routine and went hunting.  After
several colours of herring swam by, I realized two disgusting things.

A) The file was random access, meaning that not all records were
   actually allocated.
B) This file, due to its size, needed three TSLs, but only had two.
   Also, the missing TSL was the middle one (sectors 122-243).

The bug : If the current TSL does not have a pointer to the needed sector,
DOS will seek back to the first TSL and follow the links until it finds
A) the desired TSL, or
B) finds the end of the TSL list, in which case it seeks back to the
   first TSL and... (repeat ad infinitum).

	Share and Enjoy!

	Dieter Muller
	{lanl|unmvax}!nmtvax!djm

Message-ID: <4500014@uok.UUCP>
Date: Tue, 19-Feb-85 13:41:00 EST
Article-I.D.: uok.4500014
Posted: Tue Feb 19 13:41:00 1985
Date-Received: Fri, 22-Feb-85 10:07:57 EST
References: <258@nmtvax.UUCP>
Lines: 24
Nf-ID: #R:nmtvax:-25800:uok:4500014:37777777600:1038
Nf-From: uok!chumphre    Feb 19 12:41:00 1985


 Thank you Mr. Muller for your helpful information, I have 10's of disks
with this exact problem; but since my power supply bit the bit bucket
I have no way to fix them.  Could you possibly tell us netlanders how
to fix a power supply?  I know that you yourself have gone through
several.  
  It all started about 3 months ago when I flipped the switch on and
nothing but garbage appeared on the screen.  Eventually, the power
supply would warm up enough to run my one disk drive for a few minutes;
but after that few minutes the 12v output dropped too low to run the
spindle and stepper motors simultaneously.
  Now it takes about 6 hours befor the computer has enough power to 
generate a fully synchronized video signal.
  Is there anything I can do about this other than shelling out the
$45 for a power supply exchange?  
  Any help would be greatly appreciated.



		Jay McGinnis
		...!ctvax!uokvax!uok!chumphre

P.S.  The first part of this message is jokingly facetious.  Also, are
      you still using that same old Apple II ??