[Simh] Assorted ramblings was: Re: VAX Tape Emulation?

[Armistead, Jason]

Clem and all

Your knowledge of this and many other obscure (and not-so-obscure) subjects from the “early days” never ceases to amaze me.  If only there was a way to capture all these anecdotes  into one coherent “Wikipedia of computing history” …  Many of these stories are absolutely fascinating, and often amusing too.  Whether it’s the “he did / she did *THAT* … (which still lives on today)” or “we had to do this because of <some bizarre limitation>” or “we cobbled this together with a few parts lying around in the labs at <fill in the company>”, they are great to read.

Keep sharing the stories !  Long live the glory days of computing !

Thanks
Jason A.

From: Simh [mailto:simh-bounces at trailing-edge.com] On Behalf Of Clem Cole
Sent: Thursday, 25 January 2018 6:44 PM
To: Mark Pizzolato
Cc: SIMH; Larry Baker
Subject: [External] Re: [Simh] VAX Tape Emulation?



On Thu, Jan 25, 2018 at 4:57 PM, Mark Pizzolato <Mark at infocomm.com<mailto:Mark at infocomm.com>> wrote:
I think the documentation comment “cannot write variable-length blocks and do not allow skipping forward over records between read operations” was written when talking about the common cartridge tapes that were available on 80s and 90s Unix workstations.  I don’t recall the name.
That was not UNIX, that was the QIC standard.   Yes, those were blocked at 512 bytes.   Apollo's domain systems had a b*tch of time with them because their standard disk block was 1056 bytes​


  These things only supported fixed block size operations and not variable record lengths (i.e. 80 byte tape labels, then different sized data records, etc.).
​Right the 80 byte ANSI label, then different length data records.  UNIX handles that fine, even with RMT.​  FYI: My grad school housemate, Tom Quarles (of SPICE3 fame) wrote the ANSI tape and bunch of other tape support that most UNIX systems used, explicitly so he could read/write VMS tapes for the DEC guys who were doing some of the funding of the USB CAD lab.   Leffler (who wrote rmt) used Tom's tape stuff for the original debug of rmt.



  Given that the remote tape drive was a drive which could do variable length record activities, I think MultiNet’s rmt support actually worked well.  I don’t remember testing it though.  Whether someone should try to do that now to backup simulated VMS systems is another subject I may write about a little later.

​Understood.   I was just suggest​ing trying to keep another emulated system out of the scheme and going directly to the remote device either through DECnet or rmt or maybe even using a NAS as virtual tape files.   It just seemed running a Linux with a tape and then running an emulated VAX on top of that seemed like an extra layer of indirection if there was an easier path.


​
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