Date: Tue, 8 Dec 1998 19:49:40 +1100 (EST)
From: Dave Horsfall <dave@fgh.geac.com.au>
To: Michael Sokolov <msokolov@harrier.Uznet.NET>
cc: pups@minnie.cs.adfa.edu.au
Subject: Re: 9-track tape interfaces
In-Reply-To: <199812080719.MAA16509@harrier.Uznet.NET>
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On 8 Dec 1998, Michael Sokolov wrote:

> on an individual basis. Some of these go to different outputs of a 74S241
> (dual 4-bit 3-state buffer), some go to a 7437 (unfamiliar with this IC),

>From my TTL Data Book: Quadruple 2-input positive-NAND buffer (Y=AB bar).
Outputs are 3, 6, 8, 11.  Corresponding inputs are 1/2, 4/5, 9/10, 12/13.
Vcc is 14, GND is 7.

>    Hmm, this is another big gap in my knowledge. What does streaming vs.
> non-streaming mean?

Streaming means that data can be supplied to the tape (or read from) fast
enough to keep it moving, as opposed stop/start (or more likely, stop
backspace start).  Requires double-buffering somewhere.

>    Yet another gap in my knowledge. I remember seeing the term "vacuum
> columns" in the BSD documentation and having no idea what are they. Could
> you enlighten me?

ROTFL :-)  Look at an old Sci-Fi movie some time, in particular the
obligatory IBM tape drives spinning back and forth.  The vacuum columns
were buffers; columns into which bits of the tape were sucked so as to
keep the tape moving past the heads at constant velocity (not sure how
good the clock recovery was in those days) whilst the reels did their
thing.  The column has various pairs of pressure sensors, between which
the tape was kept for that particular mode; if it crept past one hole,
it upset the pressure differential, and the pumps came into play...

Remember, folks; this real-time stuff was *before* micro-chips!  I still
remember looking at the old Cipher (I have the magic codes somewhere, that
allowed it to load with the door open etc) aghast that it had no vacuum
columns, but swing-arms instead...

> > (I'm sure someone will
> > now chime in about the days when Univac UniServo drives ruled the
> > earth...)
>    
>    Just out of curiosity, what are they?

Big BIG tape drives - real Sci-Fi material :-)

-- 
Dave Horsfall VK2KFU  dave@geac.com.au  Ph: +61 2 9978-7493 Fx: +61 2 9978-7422
Geac Computers P/L (FGH Division) 2/57 Christie St, St Leonards 2065, Australia