Re: 9999

[Bob Flood <bflood@SLAC.Stanford.EDU>]

At 11:44 AM 9/9/1999 -0500, you wrote:
>
>The story as I understand it is that back in the
>"old days" many computers were programmed to consider 9999 in a program
>as the end of the program or a command to stop the operation.

But wait! There's more!

9999 was indeed used by some programming languages in the 60s as a quit
command, sort of a shorthand way to tell the computer to close all open
files the program is using and then terminate the program. It is unlikely
that any software is still running today using such languages - operating
system changes over the decades since then have probably rendered them
obsolete and unusable.

Another possibility has to do with file dates. Back in the same era, when
cpu speed, memory, and storage space were nothing like today, programmers
worked hard to execute various tasks using the least amount of system
resources and making the system as responsive as practical to the user. A
common technique had to do with storing in-use data in temporary files
(originally on tape, later on disk) rather than in RAM. When the user was
done with those files, rather than hold up things with a delete process,
programmers would simply close the temporary file and set its file date to
9/9/99, which was an indicator that the file was not going to be used any
more. When the user logged off, the system would then go back and
systematically delete files with a 9/9/99 date. I don't know how long
programmers held onto this practice, but imagine if your bank is using code
developed by an old-timer who programs this way because "we've ALWAYS done
it that way."

Have a nice day.

===================================
Bob Flood
Dosimetry Group Leader
Stanford Linear Accelerator Center
(650) 926-3793
bflood@slac.stanford.edu
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html