!lm10
!rm76
Commented Listing of DOS 3.3 RWTS

Last March I started out this series of DOS listings with the RWTS portion of DOS 3.2.1.  Since then I have printed all of DOS 3.2.1 and DOS 3.3 from $B800 thru $BFFF, except for DOS 3.3 RWTS.  Somehow it almost was overlooked, but here it is now.

There are minor differences between the two versions of RWTS, which you can find by comparing the listing from the March 1981 issue of AAL and this one.  The differences start at line 1810.  I suppose the changes are meant to be improvements, but most of them seem to make very little difference.

One critical major difference:  DOS 3.2.1 and previous versions use sector numbers which are actually written in the headers.  DOS 3.3 uses two different sets of sector numbers:  physical and logical.  The physical sector numbers are recorded in the sector header blocks; logical sector numbers are used in RWTS calls and File Manager calls.  The translation is performed using the table at line 4280, which I have called the PHYSICAL.SECTOR.VECTOR.  This table is accessed at line 3310: the logical sector number is in the Y-register, and indexes into the physical sector vector to pick up a physical sector number.
