Anecdote - Secretary vs. Backup Instructions

In the early 1980's…


We had a VAX-11/750 (IIRC) with multiple dumb terminals (24x80) hung off of it.


I noticed that most programmers did not logout before going home at the end of the day.


I noticed that our secretary used to arrive to work before all of the programmers arrived.


I asked the secretary to perform  backups every morning before the other programmers arrived.


I wrote out instructions in the form:


If you see "> ", type LOGOUT <return>

If you see "LOGIN:", type BACKUP <return>

When you see "PASSWORD:", type <…>

When you see ">" type BACKUP



About a week later, I came in early, after the secretary had arrived, but before all of the other programmers had arrived.


I saw 

"

LOGOUT

LOGIN:

>

LOGOUT

LOGIN:

>

"

on every terminal.


I asked the secretary what happened.  I got 2 answers:


  1. Backups never succeeded.
  2. The secretary never typed the word BACKUP and was always typing LOGOUT.

Conclusion

I had assumed that my instructions were sequential.


The secretary started reading the instructions from the top after every operation.


The single sheet of instructions was a parallel set of instructions in the secretary's mind, but serial in my mind.