29 Jul
2005
29 Jul
'05
2:14 p.m.
>>>> "Allison" == Allison
<ajp166 at bellatlantic.net> writes:
> ...
> Ok, so where physically is LBA 0? On most disks it is cyl 0 track
> 0 sec 0. But not on the RX50; there it is cyl 1 track 0 sec 0.
>
> So what LBA lives on cyl 0 track 0 sec 0? Answer: I'm getting too
> confused in the arithmetic, but it's an LBA in the range 790 to
> 799.
Allison> snipped...
Allison> OK, that applies to NON CP/M and DOS disks and I can see how
Allison> it would be a PITA to create DOS or CP/M media from other
Allison> DEC systems. Having done it in the past those memory bits
Allison> were lost. ;) Mostly due to trying to do the reverse (DEC
Allison> OSs from CP/M hardware).
Allison> I see no other impact to the Rainbow from the RX50.
I don't actually know the Rainbow, but I have a bit of code elsewhere
that contains this comment:
/* Convert block number to cylinder, head, sector for RT11-RX50.
* This is different for RT11 than for Rainbow DOS:
* For DOS, for cylinders 2 through 79, the sectors are interleaved 2:1.
* (DOS capability is not supported in this RT11 version).
* For RT11, all sectors are interleaved 2:1, and each subsequent
* track has the first logical block offset by 2 more sectors.
*/
So the implication is that Rainbow RX50s are still weird, but weird
differently than PDP11 ones. I don't have more detail than that, and
I don't remember the origin of that comment.
paul