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

[Johnny Billquist]

On 2019-06-26 19:54, Bob Supnik wrote:
> Implementing a more complete form of read/write/write check header is 
> not as straightforward as I thought, because the RP and RM drives use 
> different header formats.
> 
> The RP expects 4 16 bit words, of which the first two are used, and the 
> second are "for software". Word 0 is cylinder plus 18b/16b, word 1 is 
> sector, words 2 and 3 are "keywords".
> 
> The RM expects 2 16 bit words, both used. Word 0 is cylinder plus 
> 18b/16b plus two bad block indicators. Word is 1 is track and sector.
> 
> The simulator supports the RP06, RP07, RM02/3, RM05, and RM80. I'm not 
> sure if the RP07, RM05, or RM80 were ever actually qualified for the 
> KS10. However, the RP06 and RM02 both shipped with the system, so the 2 
> word/4 word distinction would have to be implemented.
> 
> I can't find the sector format for the RP07 which, despite its name, 
> behaved like an RM series drive.

The RP07 is actually even more complicated. I wrote a formatter for RSX 
for it at one point. It was more of a hack than really properly doing 
the formatting. As far as I remember, for the RP07, you can even specify 
the gap between sectors, which potentially allows you to map around bad 
spots on the disk. So there is information about that kind of things in 
the header as well.

I can't remember where I got the RP07 information from back then, but 
probably the set of microfiches we had.

I would vote for someone doing just the naive write as a starting point. 
I think much software will be happy enough with just that, and then we 
can look at specific when we locate software that really do care about 
what is written into the headers.

   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