[Info-vax] Assistance needed!! working RM05 drive and VAX needed for proje

[terry-...@glaver.org]

On Thursday, September 28, 2023 at 6:55:22 AM UTC-4, Johnny Billquist wrote:
> Nope. The RM05 supposedly will not work on the RH11. Too slow for the 
> disk. RH11 only supported RM02, RP04, RP05 and RP06. 
> 
> The RM02 was a slowed down RM03 for that specific reason. 

A Certain Large Bank paid DEC a lot of money way-back-when to investigate
the issue (it was holding up a mass migration from 11/70 to 11/84 systems).
It turned out that a minor change to the RH11 allowed the RH11/Unibus to
keep up, and the migration proceeded. DEC wasn't interested in publicizing 
the change - everyone with RM02 drives on RH11's would be complaining.

> As for SMD - not sure. DEC certainly used those OEM drives, but for some 
> reason the capacity was always less than the original drive, which makes 
> me wonder if DEC did something more funny as well. 

It might have been so they could have similar rated capacities for 36-bit vs.
16/32-bit hosts. SMD manufacturers generally provided long lists of sector
size select settings and left it up to their customers to select sector sizes
and capacities. You get a fixed number of bits/track, so larger sector sizes
are generally a capacity win due to decreased overhead, except when that
takes you over the bits/track limit and capacity/track drops back in those
tables.

But manufacturers do some weird stuff. MAI Basic Four sold rebadged
Calcomp Trident T-50 drives and rated them for 30MB or something weird
like that.