Looking for early versions of MicroVMS & VWS

Ethan> On Tue, Mar 24, 2009 at 3:30 PM, Paul Koning Ethan> <Paul_Koning at dell.com> wrote: >> >> ?Ethan> ...and I don't know if a uVAX-I can keep a TK50 ?Ethan> >> busy, ... >> >> I should hope so, given that a modest PDP-11 could do so easily. Ethan> I wouldn't be so certain - my experience is that the the way Ethan> the TK50 works, you can store *up to* 95MB per tape *if* you Ethan> can keep the silos full. A MicroVAX-I is a slooooow beasty. Ethan> There's no problem with the Qbus itself, but my concern would Ethan> be that system overhead, interrupt latency, RQDX performance, Ethan> etc., could be bad enough that the OS just couldn't fill tape Ethan> buffers fast enough. Of course, trying to back up 30 MB onto Ethan> a 95MB tape doesn't require perfect performance. Ethan> Thinking about it, perhaps it's worth the effort to use Ethan> Standalone Backup - that should minimize any OS effects on Ethan> backup speeds. Once the tape is written, ISTR the TK50 will Ethan> back the tape up as necessary to extract what's on it. It's Ethan> writing that you _must_ optimize. That doesn't sound familiar. I thought the rule of all streaming tape drives was that they get very slow if you don't keep the buffers full, but there isn't any impact on capacity. I've never heard of any. It may be that there was and the designers kept it secret out of embarassment... RSTS on an 11/73 driving an TU50 would stream quite well (with Backup). Is a MicroVAX-I slower than that? Or does RSTS do streaming I/O better than VMS? (I suppose that's possible...) Interrupt latency shouldn't be much of an issue; the thing is that you have to queue up multiple buffers. paul