Subject: Re: dataflow basics
From: (Rob Warnock)
Date: Sun, 08 Apr 2007 22:42:13 -0500
Newsgroups: comp.lang.lisp
Message-ID: <>
[ob. OT warning...]

Ken Tilton  <> wrote:
| Who says we cannot have fun with data names? One crucial variable out 
| there in a business application somewhere is a flag indicating if 
| something had been altered: ch-ch-ch-ch-changes.

Circa 1968, RCA came out with the Spectra 70 series of IBM System 360/370
compatible mainframes. This was in the days when "bus/tag"-style channel
I/O came in only two flavors: "byte multiplexor", and "selector". The
"byte-mux" could interleave traffic from a number of I/O devices, but
could only move one byte per entire I/O transfer, so the overhead was
high and the speed low -- it was very easy to overrun even a medium-speed
device if too many devices were active at once. The "selector", on the
other hand, could move large blocks at high speeds, but was locked to
a single device for the entire duration of the transfer, which sometimes
caused performance problems with other devices on the same channel if you
did an I/O that had *long* latency [like a non-detached tape rewind].

So the RCA Spectra 70 added this extra little wire to their byte-mux
channels that permitted the device to request a limited burst mode
of several bytes, which provided a compromise between the two types.
The wire was to be asserted when the device was in danger of falling
behind, in order to let it catch up with the data rate. And the name
they gave to the wire...

[wait for it...]



...was "CATSUP".


p.s. There were lots of other fun wires deep inside the core of
the Spectra 70 as well, named for secretaries, babies, pets, etc.
Those engineers knew how to have fun.

Rob Warnock			<>
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