[Simh] DEC floppy disk interleave questions

[Johnny Billquist]

Hi, Alan.

On 2015-03-08 00:47, Alan Frisbie wrote:
> I have a large quantity of disks that I wish to copy to files
> that can be directly used by the SIMH PDP-11 emulator and by the
> E11 emulator.   They include 8" floppies (both RX01 and RX02),
> RL01, and RL02.
>
> The issue is that the disks have sector sizes that differ from
> the usual 512 bytes, as well as having interesting interleave
> and stagger factors.   RX50 (and RX33?) disks have (I think)
> 512-byte sectors, but some odd track usage.   I also believe
> that RX02 disks have the first track in single-density mode,
> just to complicate things, but it isn't used by most DEC O/S
> software.   RL01 and RL02 disks also have bad-block sectors
> at the end of the disk.
>
> I am assuming that SIMH and E11 emulate the device faithfully
> enough that programs which are aware of the interleaving and
> small sector sizes will work properly.   If this assumption is
> wrong, please enlighten me.
>
> If my assumption is correct, what is the best way to copy the raw
> disks (which are in a variety of O/S formats) to files which the
> emulators will be happy with.   I can bring up a real PDP-11 with
> RX02, but will probably be using a microVAX-II with an Andromeda
> FDC11-B controller and Shugart 800 drives.   I don't mind writing
> my own code with QIOs.
>
> I have a bunch more questions related to this, but this will
> do for now.   :-)
>
> All of this is related to cleaning out my storage units and
> de-cluttering my life.

Hmm, I believe this is not absolutely straight forward. The problem is 
that simh (or E11) do not emulate the physical layer, but the logical one.
As such, the image files of disks are assumed to always be containing 
sequential blocks, and no block headers are in the image file.
So, it will work, in that, if you can dump out an image from a disk, 
where block #1 is block #1 on the image file, then things will just work 
fine.
If you dump out the physical blocks raw, including block headers, then 
they are not usable by the emulators.
Logical rearranging of blocks will work fine, though. So, the trick you 
normally see with RX01/RX02, where they remap block numbers to other 
blocks numbers in the device driver, is just fine. You just want the 
actual physical blocks, in the order they are on the disk. )As indicated 
by the disk block headers.) The actual layout, as created when 
formatting the disk, will not carry over, but it is also not important.
(I hope I'm making sense here, I feel I might be overcomplicating my 
text...)

Bad blocks, as described by the RL01/RL02 bad block tables, are totally 
under the device drivers and system software, so that is just fine. 
Systems will avoid those blocks, even on a dumped image of the disk, 
assuming you copy all blocks, including the bad block list.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol