Discovery: Excessive reads of VTOC (Volume Table of Contents)

[TommyGH]

I continue to examine DiversiDos changes to DOS3.3 and have discovered an interesting enhancement, which speaks "volumes" about the DOS3.3 poor design.

1. Boot a DOS3.3 disk (APPLEII+ emulation)
2. F7

Put a breakpoint at DOS3.3 symbol VTIO ($AFFD). This is the common path for reading and writing the VTOC.

3. BP AFFD

4. F7

5. NEW

6. 10 PRINT "VTIO TEST"

7. SAVE VTIOTEST

8. Count how often the breakpoint is triggered, and each time press F7.

When VTIOTEST is not already on the disk, the VTOC is read/written 7 times.

With DiversiDos there is 1 read and 1 write of the VTOC.

You may want to document this behavior.