Scratch monkey

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A Scratch Monkey is a term used in hacker jargon, as in "Before testing or reconfiguring, always mount a scratch monkey", a proverb used to advise caution when dealing with irreplaceable data or devices. Used to refer to any scratch volume hooked to a computer during any risky operation as a replacement for some precious resource or data that might otherwise get trashed.

This term preserves the memory of Mabel, the Swimming Wonder Monkey, star of a biological research program at the University of Toronto. Mabel was not (so the legend goes) your ordinary monkey; the university had spent years teaching her how to swim, breathing through a regulator, in order to study the effects of different gas mixtures on her physiology. Mabel suffered an untimely demise one day when a DEC field engineer troubleshooting a crash on the program's VAX inadvertently interfered with some custom hardware that was wired to Mabel.

It is reported that, after calming down an understandably irate customer sufficiently to ascertain the facts of the matter, a DEC troubleshooter called up the field service manager responsible and asked him sweetly, "Can you swim?" Not all the consequences to humans were so amusing; the sysop of the machine in question was nearly thrown in jail at the behest of certain members of the local 'humane' society. The moral is clear: When in doubt, always mount a scratch monkey.

The actual incident occurred in 1979 or 1980. There is a version of this story, complete with reported dialogue between one of the project people and DEC field service, that has been circulating on Internet since 1986. It is hilarious and mythic, but gets some facts wrong. For example, it reports the machine as a PDP-11 and alleges that Mabel's demise occurred when DEC PMed the machine. Earlier versions of this entry were based on that story; this one has been corrected from an interview with the hapless sysop:

Date: Wednesday, 3 September 1986  16:46-EDT
From: "Art Evans" <Evans@TL-20B.ARPA>
To:   Risks@CSL.SRI.COM
Re:   Always Mount a Scratch Monkey

In another forum that I follow, one correspondent always adds the comment
        Always Mount a Scratch Monkey
after his signature.  In response to a request for explanation, he
replied somewhat as follows.  Since I'm reproducing without permission,
I have disguised a few things.

              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

My friend Bud used to be the intercept man at a computer vendor for
calls when an irate customer called.  Seems one day Bud was sitting at
his desk when the phone rang.

    Bud:        Hello.                  Voice:  YOU KILLED MABEL!!
    B:          Excuse me?              V:      YOU KILLED MABEL!!

This went on for a couple of minutes and Bud was getting nowhere, so he
decided to alter his approach to the customer.

    B:          HOW DID I KILL MABEL?   V:      YOU PM'ED MY MACHINE!!

Well to avoid making a long story even longer, I will abbreviate what had
happened.  The customer was a Biologist at the University of Blah-de-blah,
and he had one of our computers that controlled gas mixtures that Mabel (the
monkey) breathed.  Now Mabel was not your ordinary monkey.  The University
had spent years teaching Mabel to swim, and they were studying the effects
that different gas mixtures had on her physiology.  It turns out that the
repair folks had just gotten a new Calibrated Power Supply (used to
calibrate analog equipment), and at their first opportunity decided to
calibrate the D/A converters in that computer.  This changed some of the gas
mixtures and poor Mabel was asphyxiated.  Well Bud then called the branch
manager for the repair folks:

    Manager:    Hello
    B:          This is Bud, I heard you did a PM at the University of
                Blah-de-blah.
    M:          Yes, we really performed a complete PM.  What can I do
                for You?
    B:          Can You Swim?

The moral is, of course, that you should always mount a scratch monkey.

              ~~~~~~~~~~~~~~~~~~~~~~

There are several morals here related to risks in use of computers.
Examples include, "If it ain't broken, don't fix it."  However, the
cautious philosophical approach implied by "always mount a scratch
monkey" says a lot that we should keep in mind.

Art Evans
Tartan Labs