[Simh] HSC vs UDA/QDA

[Johnny Billquist]

On 2017-03-08 22:15, Bob Supnik wrote:
> The HSC family offered a superset of capabilities compared to the
> UDA50/QDA50. In particular,
>
> - tape as well as disk support (TMSCP as well as MSCP);
> - controller-based disk to tape backups and tape to disk restores;
> - controller-based disk to disk duplication;
> - controller-based volume shadowing (RAID 1).
>
> UDA50/QDA50 did not support tape drives, disk duplication, or
> controller-based volume shadowing.
>
> HSC supported some data caching; UDA50/QDA50 did not.

Oh. I didnät mean to imply that the HSC was just the same as an UDA. But 
the MSCP protocol as such is the same between them. Shadowing, local 
disk copying, caching and so on, are just things a controller can do 
without the host are even aware of it happening.
But since we're talking emulation, the actual disks now might be doing 
even more of that than an HSC ever could. It's not really something that 
makes much sense to emulate.

And yes, an HSC could also attach tapes. Which would then be pretty much 
the same deal as if you had a local controller for TK50/TK70 or TU81, 
which also talks TMSCP. But once more, the transport is different than 
CI. But you end up talking to a TMSCP server in both cases. The DSA was 
designed to be the same no matter what the transport or disk interface 
technology looked like. There is certainly some point in that idea. 
We've sortof reinvented that lately with SCSI...

	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