TITLE
ProDOS 1.1.1: Track O not Automatically Protected 

Article ID: 2121
Created: 1/20/87
Modified: 2/25/98

 

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TOPIC 
In ProDOS 1.1.1 and ProDOS 8 v1.2, part of the Disk II I/O driver code causes 
occasional trashing of track 0.



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DISCUSSION 

ProDOS 8 v1.3 and 16 were changed to solve this problem, first reported in the 
January 1986 issue of Open Apple. An Applesoft solution appears in the November 1986 
issue in an article entitled "ProDOS bug found in Australia".

The beginning code of the driver performs a series of instructions intended to 
de-activate any UniDisk 3.5's that may happen to be on line.

The problem occurs when these instructions cause a clash on the disk drive port 
data lines. The clash may put in write mode any 5.25" disk drive (Disk II, UniDisk, Apple 
5.25, DuoDisk, or Apple IIc external drive). ProDOS 1.1.1 and ProDOS 8 v1.2 do not check 
for this re-setting, so they act as if the 5.25 drive were in the read-only state (which 
it is under normal circumstances).

The next time these versions of ProDOS attempt to access a 5.25 disk, they wipe out 
what they would normally read. In many cases, the directory is wiped out because 
many applications check the directory in order to open a file.