[TUHS] Ultrix Tape: Block Size?

[Paul Koning]

> On Oct 16, 2018, at 1:23 PM, William Pechter via cctalk <cctalk at classiccmp.org> wrote:
> 
> DEC Tape II was the serial driven TU58.
> The TK50 was CompacTape or something like that.  It was the predecessor of a number of square tapes...
> 
> See DLT on Wikipedia https://en.m.wikipedia.org/wiki/Digital_Linear_Tape
> 
> Bill
> 
> -----Original Message-----
> From: Paul Winalski <paul.winalski at gmail.com>
> To: Clem Cole <clemc at ccc.com>
> Cc: The Eunuchs Hysterical Society <tuhs at tuhs.org>, cctalk at classiccmp.org
> Sent: Tue, 16 Oct 2018 13:14
> Subject: Re: [TUHS] Ultrix Tape: Block Size?
> 
> On 10/15/18, Clem Cole <clemc at ccc.com> wrote:
>> #$%^ - they >>weren't<< like DECtape from a reliability standpoint ...
>> ᐧ
> The original DECtape was extremely reliable.  Not so the TK50.
> Calling it "DECtape II" was an insult to the original DECtape.  The
> problem wasn't so much the drive itself, but the controller.  In an
> effort to reduce costs, DEC used a controller that had insufficient
> buffering capability for a streaming, block-replacement tape device
> such as the TK50.  TK50s were prone to both data-late and overrun
> errors.

DLT is something entirely different from "DECtape II" -- that is a little rubber band driven cartridge, extremely slow and extremely lousy.  DLT is fast, 1/2 inch tape, serpentine recording.  It's the direct ancestor of a whole series of cartridge tapes of ever increasing capacity.

I used DLT on RSTS systems, with a Qbus interface.  Those were modest speed hosts and buses, but I never remember data late or overrun issues, and we drove those tapes quite hard in full time streaming mode for backup and software distribution.  Longer blocks, too (2k or so) which would make any buffering issues more severe.