'Fat tracks in emulation'
Author:J Achernar (registered user: 36 posts )
Date: Tue, Nov 16th, 2010 @ 18:41 ( . )

I have been working on Music Construction Set and have observed the behavior described in this thread. In WinVICE 2.2, the program will load, attempt to read the fat track, then reload aligned to the half tracks, read the fat track successfully and then start. I also tried the trick mentioned in this thread of starting an auto load of the program, resetting and doing a manual load. In this case, the manual load completes successfully in one pass. I believe that this is a limitation in WinVICE. CCS64 reads it successfully in one pass.

The other floppies that I have with fat tracks are not EA and don't exhibit this behavior.

I have tried this with a G64 made with only full tracks, a G64 made with all half tracks and a G64 patched so that all four half track pointers point at the same track in the G64. None of this makes any difference in WinVICE. This tells me that WinVICE does not actually read the half track data in the G64. Otherwise, it should have failed to load the all half track image, on the second half track aligned read pass, since half tracks 1.5, 2.5, etc. contain garbage data.

With CCS64 there is also no difference in behavior between any of these three versions. I don't think that it actually reads half tracks either, but I can't confirm this.

In the case of backup programs not being able to reproduce the fat track, I believe that some could. My backup copy is not patched when compared to my original. I believe that I made it using Fast Hackem using my 1571 (if that makes a difference). Also, when looking at an image of it scanned with all half tracks, it looks to me that the NIB contains good data on 34.5 and 35.5. I am not very experienced with the internals of NIB files. I have sent the NIBs of my original and my backup to Pete. Maybe he can confirm whether or not the backup successfully reproduces the half tracks.



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