[Info-vax] DLT drives and antique SCSI compatibility (was: Re: Next release of OpenVMS x86_)

[Stephen Hoffman]

On 2020-07-14 12:13:00 +0000, Simon Clubley said:

> On 2020-07-14, Terry Kennedy <terry-groups at glaver.org> wrote:
>> 
>> I asked about this when doing the menus - using a second unit number to 
>> boot VAX code wouldn't have been hard, but I was told to just stick to 
>> the PDP-11 side. The impression I got was that none of the VAX groups 
>> wanted it. They were either heavily invested in DSSI or already had 
>> their own limited-function SCSI boards.

DEC wasn't too fond of SCSI back then and for various reasons, 
including both technical and business reasons.

KZQSA was itself very limited in what was supported on the SCSI bus.

Similar restrictions for the DEC 2000 / DECpc AXP 150 / Jensen Adaptec 
SCSI permissible configurations.

And the Q-bus boards and drivers I was working on then ran afoul of the 
KFQSA, but that's DSSI and not SCSI, and the KFQSA is all fodder for 
another discussion.

For various at DEC, DSSI was preferred to SCSI as it was multi-host and 
multi-initiator capable, viewed as better-specification, and was 
DEC-proprietary hardware, etc.

I too preferred DSSI back then. You plugged it in. It worked. SCSI back 
then... less so. Tri-host DSSI was useful for clustering. We still 
don't have a DSSI analog, either. USB doesn't provide multi-initiator, 
last I checked. Ethernet-related is the closest.

> I wonder if the DEC-specific SCSI hardware will run on any x86-64 box 
> which has a SCSI adapter and I wonder if VSI has provided support for 
> such devices within x86-64 VMS ?
> 
> A TZ30 attached to a Dell box running x86-64 VMS. Now there's an 
> interesting concept. :-)

TZ- and RZ-class hardware probably will work, as much as anything 
associated with SCSI from that era is compatible. And as much as any 
hardware from that era still works. And can find still-working 
CompacTape-era DLT cartridges.

VSI has some "fun" ahead, with the hardware compatibility lists for 
OpenVMS x86-64, that possibly involving third-party or end-user 
integration and testing, and the TZ30 likely won't be included on the 
support lists.


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