> On Sep 14, 2017, at 4:47 PM, Warner Losh <[email protected]> wrote:
>
>
>
> On Thu, Sep 14, 2017 at 2:44 PM, Paul Koning <[email protected]
> <mailto:[email protected]>> wrote:
>
> > On Sep 14, 2017, at 4:39 PM, Warner Losh <[email protected]
> > <mailto:[email protected]>> wrote:
> >
> > ...
> > I don't see where you read the first 2 tracks uninterlaced, and the other
> > tracks interlaced? For DOS formatted disks, that's what's required. While
> > screwing up the first two tracks won't affect your ability to read DOS
> > floppies (since they were reserved for the boot blocks), other formats
> > aren't so forgiving and it makes the disk unbootable...
>
> The question was about RX50 disks, which are uniformly interlaced and skewed.
>
> No. They are not. CP/M MS-DOS on the Rainbow didn't do it uniformly. Venix on
> the Rainbow did it a different way. They are not uniform, and the first two
> tracks were not skewed. The DECMATE did it differently (not skewing tracks 78
> and 79). I'm unsure how other OSes handled things, but it was anything but
> uniform.
>
> I wrote IMPDRIVE back in the day to read 3.5" floppies and had to cope with
> this. I have the BIOS listing for MS-DOS that shows clearly that the first
> two tracks weren't skewed. I also have the CP/M listing, but don't have it as
> handy. I'm quite certain of the non-uniformity.
I guess I missed the fact that Rainbow did things differently. What I said is
valid for MSCP and Pro RX50s. Thanks for the correction.
paul
