[Simh] RP/RM differences in header commands (for ITS, salvager)

[Paul Koning]

> On Jun 28, 2019, at 3:07 AM, Johnny Billquist <bqt at softjar.se> wrote:
> 
>> From a hardware point of view, sector header "Word 3" and "Word 4" have
>> no particular meaning.  Just for completeness, can you point me to a
>> reference where "pack number" is defined or used by the software?
> 
> Search for DEC standard 144. If nothing else, I think there is a description in the RL11 documentation. (Me trusting my memory once more...)

That's different, though.  It describes the bad block table, which includes a pack serial number in its header.  Some device types use 144, some do not (in particular, on RP/RM there is a mix -- RP04/5/6 do not, RP07 and RM02/3/5/80 do).  The 144 table is purely a software construct, a bit of data placed by convention in the last few sectors of the drive and interpreted by the OS.  For example, in RSTS the bad block table is read to mark those blocks as unavailable, and the serial number is read and displayed during formatting but not otherwise used for anything.

	paul