28 Jul
2005
28 Jul
'05
11:30 p.m.
Subject: Re: DEC Rainbow disks - help
From: Paul Koning <pkoning at equallogic.com>
Date: Thu, 28 Jul 2005 17:42:48 -0400
To: cctalk at classiccmp.org
snipped...
OK, that applies to NON CP/M and DOS disks and I can see how it would be
a PITA to create DOS or CP/M media from other DEC systems. Having done
it in the past those memory bits were lost. ;) Mostly due to trying to
do the reverse (DEC OSs from CP/M hardware).
I see no other impact to the Rainbow from the RX50.
Allison
>>>> "Allison" == Allison
<ajp166 at bellatlantic.net> writes:
> The other confusing point is the addressing:
logical block 0 is at
> the start of track 1, the sectors are 2:1 interleaved, and
> physical track 0 holds the LAST 10 logical sectors...
Allison> ???? CP/M disks nominally start logical block 0 after
Allison> system tracks. Dos disk are different and I never paid much
Allison> attention to them. POS for the PRO was same media but file
Allison> allocation was different again from CP/M or DOS [or RT11 and
Allison> VMS as well] on RX50.
I'm not talking about the file system, I'm talking about block
numbering -- the linear block numbers (0 to 799) which sit underneath
the file systems. All the DEC PDP11 and VAX OSs use linear block
addressing; the sector/track/cylinder structure of the drives exists
below the file system only, and is mapped to LBA by the disk device
driver.
For example, on all disks, LBA 0 is the boot block.
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.