Re: Volume Table of Contents question for Dos 3.3

[David A Lyons <dlyons@apple.com>]

In article <93179.092237F0O@psuvm.psu.edu> , F0O@psuvm.psu.edu writes:
>    I'm using Dos 3.3 on an apple IIe and need to write out at the sector
> level using the RWTS subroutine.  I want to update the track bit maps
> in the volume table of contents as I go along.  All so far is fairly
> simple.  My question is with 30h - 33h in the VTOC.
>    In the Dos manual the description is: "These 4 bytes are a mask for
> the track bit maps: each 1 bit enables one of the 16 sectors to be used
in
> every track."
>    I'm not sure why you would need to have a mask for the track bit
maps.  It
> seems redundant to me.  If in the track bit map, you are marking the
sector as
> either being free or used, what more do you need?
>    Could someone please enlighten me as to what I don't understand. 
Thank
> you for your support!

Since there are four bytes involved, there are 32 bits available,
compared to the 16 sectors per track that you typically use.  So those
bytes are probably $FF $FF $00 $00 (right?).

As I recall, when I used a Sider hard drive with DOS 3.3 partitions
(quite a few of them, actually), those partitions used all 32 sectors per
track (*and* had more then 35 tracks...I don't remember the maximum
tracks allowed by the VTOC structure).

I don't have any DOS 3.3 reference material in front of me, but maybe
that will be enough info to get you going.

Dave Lyons, dlyons@apple.com
Mr Tangent

My opinions are my own, not Apple's.