[Info-vax] DLT drives and antique SCSI compatibility

[Chris Scheers]

Stephen Hoffman wrote:
> On 2020-07-10 21:58:28 +0000, Terry Kennedy said:
> 
>> To comment on another reply, I was told by a reliable source that the 
>> TZ30 was the result of a barroom bet between a DECie and a Mitsubishi 
>> engineer about the impossibility of making a half-height DLT drive. 
>> Despite the "Z" in the model name, it is *NOT* a SCSI-compatible 
>> device. In fact, it can hang both halves of the only controller it was 
>> every supported on, the RQZX1. Simple user mode I/O is sufficient.
> 
> That sounds... odd...
> 
> RQDX1 was MFM, and AFAIK was never used with a DLT.
> 
> DLT tapes were offered with the sorta-SCSI with the MicroVAX 2000 and 
> VAXstation 2000 (TK50-Z, IIRC—the TZK50 was the intended-for-SCSI 
> variant, IIRC), SCSI (TZ30, TZK50, TZ70, etc), DSSI (TF70, etc), and the 
> earliest TMSCP-based TK controllers such as the TQK50 used with the TK50 
> and TK70.
> 
> The TK50-Z was the one most folks had issues trying to use 
> else-platform, IIRC.
> 
> TZ30 was a half-height SCSI controller.  The TZ30 INQUIRY data was 
> reportedly badly bogus (ASCII NULs?), in at least some of the firmware 
> revisions. If not in all revisions. Returned identity data which then 
> hosed compatibility.
> 
> Various SCSI hardware back then was somewhere between funky and 
> mutually-incompatible, too. SCSI and ATAPI and USB and ilk are such a 
> joy to work with.

FWIW: (Which is very little these days)

IIRC, the VAXstation 2000 external TK50 was the TK50Z-Fx.  This one had 
barely enough functionality to work with a VAXstation 2000 and pretty 
much didn't work anywhere else.

The VAXstation 3100 variant was the TK50Z-Gx.  This one was much better 
for SCSI compliance and could be used on some non-DEC systems.

I think (but could be wrong) that the only differences between the -Fx 
and -Gx versions were the SCSI adapter ROMs and the -Gx had a cutout to 
access the SCSI ID switches.

-- 
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Chris Scheers, Applied Synergy, Inc.

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