DECmate II disk image tooling?

[Rick Murphy]

On 3/12/2022 3:20 PM, David Schmidt via cctech wrote:
> I have some disks that look like they're from a DECmate II computer,
> standard RX50K drives.  The disk images all look like they're a mix of
> 12-bit (OS/78 or OS/278?) and 8-bit all on the same media.  I can't
> convince PUTR to make sense of the images, so I'm wondering if there is
> anything else out there that is likely to be able to examine the disk
> contents?  I'm really looking for PUTR-like functionality to list and copy
> files.

Since it's a DECMate II, these may be WPS disks.

At least for the RX01/RX02, Those are 8-bit mode except for the boot 
sector (because the standard boot was for a 12-bit mode disk.)  I don't 
know the layout for the RX50 - since it's not using the RX boot, there 
shouldn't have been a need for a 12-bit boot sector.

It's also possible they're COS-310 disks, which also were 8-bit mode.  
Using byte mode allowed WPS and COS to use the full capacity of the 
disks.  Apparently the RX50 controller retained this wasteful 12-bit mode.

> Maybe SIMH could be configured to be a DECmate II and be fed the disks?

SIMH doesn't have an emulation for the RX50 controller on the DM2.  
There's probably a different interleave being used here, so decoding the 
layout would be a matter of trial-and-error.

The specs for the RX50 controller are available - 
http://www.bitsavers.org/pdf/dec/pdp8/cmos8/DECmate/Decmate_II_Specification_Jan83.txt 

That means that an emulator is possible.

     -Rick