Subject: Re: TK50 with KA650
To: Tom Ivar Helbekkmo <tih@KPNQwest.NO>
From: Nigel Johnson <>
List: port-vax
Date: 02/09/2000 16:46:29
A tape drive with a small buffer, such as the TK50, should always be put
at the end of the bus closest the processor.  The reason for this is that
if it can't keep its tiny buffer filled fast enough to output at the speed
of the tape, the tape will fall out of stream, and have to stop, back up,
and re-start.  Since streaming tapes do not have the expensive (and
difficult to adjust) start-stop hardware, this involves quite a run back
until a block end can be found, then running forward until the right
place, and writing.  This is why 40 minutes can turn into 8 hours!

Just my two cent's worth.

Nigel Johnson, VE3ID

Tom Ivar Helbekkmo wrote:

> Lord Isildur <> writes:
> > really? all the docs i see generally say put tape controllers at the
> > end, in low priorities.
> Not smart.  Back when I first learned this, I moved the TQK50 in a
> PDP-11 up from near the end of the bus to its proper position, and the
> time taken to write a full tape dropped from 8 hours to 40 minutes.
> Streaming is good!  :-)
> -tih
> --
> Popularity is the hallmark of mediocrity.  --Niles Crane, "Frasier"