[HECnet] DECnet-VAX V3.0, VMS V3.5 (Was Re: Oldest VAX/VMS for VAX-11/730 on HECNET) --> Supratim:vms/decnet 3.5 poisoned?

[Paul Koning]

> On Dec 16, 2021, at 7:44 PM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> On 2021-12-17 00:56, R. Voorhorst wrote:
>> Hi Supratim,
>> These tapes can be attached to the simh tdc# devices, read on Vms as Dda0: etc, and behave as disk as expected. Functioning on simh Rq (Vms Dua/b) is kind of a fluke.
> 
> Not really any fluke in it. Any disk is in the end just a bunch of sequential disk blocks. When we're talking a simulation, they are all the same on the host side. The only difference is the size.
> (Well, simh have now artificially introduced extra meta-data which have no relationship to the real world, but anyway...)
> (And things can possibly get complicated if you have interleaving involved one way or another at a level which is visible to software.)
> 
> A DECtape II is really a disk. Just a slow one. It has nothing to do with tapes, in spite of the visual similarities.

The other factor is that "rq" is MSCP, which is the DEC disk architecture that supports arbitrary size disks without software change.  And SIMH takes advantage of this with the "RAUSER" type where you can pick a size, whatever is convenient.

Using a DECtape 2 image for an emulated RK05 won't work because those only come in one size, and it isn't the one used by DECtape 2.  MSCP has no such limitation

	paul