On 8/13/2017 11:34 AM, Jerry Weiss via cctalk wrote:
On Aug 13, 2017, at 12:59 PM, Ulrich Tagge <u.ta...@gmx.de> wrote:
Hi Jerry,
I have tried with PDP11GUI, but the first message says "The image contains only
505856 bytes, but disk has 512512 bytes".
I have written some disks, and have ignored this message, but none of them is
readable under RT-11.
.dir dy0:
?DIR-F-Error reading directory
So I think the DSK format is different from the one PDP11GUI uses.
In the documentation I have seen, that the format is the same as SimH uses.
Image file format
Every DEC disk or tape is logically represented as a linear list of “blocks”.
The block size differs between 128 byte and 1024 bytes. Reading and writing is
based on block numbers.
The file format is that of SimH: a file image is just a stream of blocks.
Kermit would be a possibility, and I will try it later on.
Many Greetings
Ulrich
DEC OS’es typically do not do anything with track 0 on an RX02, and start with
track 1. I can only guess that PDP11GUI is trying to use the entire disk.
If there is an option to start at track 1 or skip the first 30 (?) blocks, that
might work.
Note that ?DIR–F–Error reading directory is a hardware error.
Bad data would instead cause a ?DIR–F–Invalid directory.
Regards,
Jerry
The RX01 physical format is 77. tracks of 26. sectors (2002. total sectors) of
128. bytes, or 256,256. bytes.
For RX02 track and sector counts are the same, but there are 256. bytes per
sector, for a total of 512,512. bytes.
The .DSK images are (usually!) a pure physical image of the disk, in
track/sector order, from track 0 sector 1 to track 76. sector 26.
The images include track 0 which is not used by any DEC O/S. The boot block /
filesystem starts at track 1 sector 1.
Note that sectors are numbered 1. thru 26. There is no sector 0.
All the DEC operating systems use interleaving of logical to physical sectors on
the RX device images, so they are unique
in the sense that the image file is not just a logical block 0. to block N-1.
image of 512. byte blocks as most/all other image files are.
If your RX02 image file is only 505,856. bytes then this is 6656. bytes (exactly
26. * 256.) too short, so it would appear track 0 is skipped.
So when someone imaged the floppy they decided to skip over track 0 (how
thoughtful of them).
You might try using unix dd to prepend 6656. bytes of zero as a header, and then
copy the rest of the data to form a 512,512. byte file.
That may work on PDP11GUI (and should under SIMH as well) ***IF*** the person
who imaged the disk just dropped track 0.
If they ALSO decided to de-interleave the physical sectors to logical blocks
then the process just got a lot more complicated.
You will then need to undo the physical/logical conversion of the sectors to
blocks to get back to a raw device image of the RX media.
