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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.
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