Date: Fri, 12 Aug 88 23:58:24 BST
From: mg@ukc.ac.uk
To: cmd@ukc.ac.uk
Subject: how to teach file permissions.

This is how I will teach file permissions this year:

Enter lecture theatre with VAX Vacuum cleaner box full of write-permit rings.

Mention Vaxen in the course of preambulatory waffle.
Make it quite plain what Vaxen are, as machines.

Spend the rest of the lecture making VAX jokes with
vacuum-cleaner double meanings.

Hold up a write permit ring.

Explain what magnetic tapes are (and were!) and why you want write
permit rings (similar to write-permit tabs on cassettes).
Say that some tape systems can let you write-permit,
say, the first half of the tape only, if it is a tape you have only
half-filled, but the data there is valuable.
This isn't true, as far as I know, but that's all part of the game.

If they have already met files, they have probably already grasped
that they must be stored on a magnetic disk somewhere, so it's probably
worth reminding them in case they should forget.

By this time, the similarity between unix file permissions and
write-protection for regions of a tape should have dawned on the
alerter students.  Would it be insulting their intelligence to state it?

Point out the similarity between unix file permissions and
write-protection for regions of a tape.

The Chinese students are still trying to understand the VAX jokes,
and have written them down to be decoded later.
They recall that everybody laughed, and since they had written it
all down anyway, they probably put an asterisk by it at the time.
(Or, more likely, the Cantonese symbol for an ass.)

Yes? Yes?

	Martin