Today I am going to retell a story from 1979 or 1980 at the University of Toronto.
At the time the star of the University of Toronto's biological research program was a monkey named Mabel.
Now Mabel was not your ordinary monkey. Researchers in the zoology department had spent years teaching her how to swim breathing through a regulator in order to study how different gas mixtures affected her physiology and performance.
Above: A monkey who is not Mabel
Mabel was popularly known as the "Swimming Wonder Monkey."
The zoology department fitted Mabel and four other monkeys with caps attached to various A-to-D and D-to-A converters that sensed the monkeys' brain waves. The monkey skullcaps were in turn connected to the zoology department's first VAX 11/780.
Here is a picture of the VAX 11/780:
At the time, the VAX 11/780 was a brand new state-of-the-art machine. It cost hundreds of thousands of dollars, took up basically an entire room, and had 2MB of memory.
So anyway, the five monkeys had skullcaps that were connected to this VAX. Researchers had written device drivers where they could run the monkeys' skullcaps off the disk drive connector.
There was a disk in the disk drive, and the disk drive was mounted read-only. The read-only button was pressed and taped over. It had a warning not to remove the tape. The system would read the data from the read-only drive and write it to a regular disk.
The monkeys were playing, swimming, and advancing science several stories away from the computer room where the VAX 11/780 was housed.
One day, the computer had a failure. Because it was still on a service contract, the zoology researchers called Digital (now defunct) to get it fixed.
The Digital Field Service technician went to the University of Toronto to run diagnostics on the malfunctioning VAX. The first thing that the technician noticed was that there was a piece of tape over the drive making it read-only. He figured, quite logically, that it must be a really important disk. So he was very careful not to mess with the data on that disk.
The technician removed the disk from the drive and put in a scratch disk. Once the production disk was safely out and the scratch disk was in, the technician removed the tape from the drive and started running diagnostics.
The diagnostics exercised the device driver interface, which was connected to the monkeys' skullcaps.
Disk drive diagnostics are designed to test the limits of the disk drive. They are not designed to be safe for monkeys' brains.
The monkeys started having convulsions. Two of the monkeys were stunned, and three monkeys drowned.
The Digital service tech was distraught. He was going to call the Humane Society and turn himself in.
Thereafter, the experiment became known as The Great Dead Monkey Project.
That is the origin of the proverb:
Before testing or reconfiguring, always mount a scratch monkey.
Hat tip: Armando Fox, author of Engineering Software as a Service: An Agile Approach Using Cloud Computing.