Re: [NTLK] [OT] It's MS-DOS 6.22 day!

From: Michael J. Hußmann <michael_at_michael-hussmann.de>
Date: Tue Jun 23 2009 - 19:55:33 EDT

Jon Glass (jonglass@usa.net) wrote:

> There was a button on the side of the Mac, called the
> programmer's interrupt or programmer's switch, that called up a little
> window, superimposed over the display. It was very cryptic. For
> example, type "G" and return to exit the window. Nothing like the
> terminal or bash or tch or anything DOS ever did...

The programmer's switch raised a non-maskable interrupt (NMI) that
invoked the debugger -- either the built-in (built into the ROM, that
is) mini-debugger, or MacsBug, a more sophisticated debugger, if the
latter happened to be installed. With MacsBug you could inspect the
contents of CPU registers, the stack, memory etc.. In practice and if
you weren't actually a programmer, the most useful commands were
"g" (resume execution from the point where the debugger was invoked) and
"es" (exit to shell) that with any luck would restart the Finder, even
when it was a crash that had brought you there. In the mini-debugger, "g
finder" was used for much the same purpose -- most people didn't realise
that the mini-debugger had no idea what "finder" meant; lots of words
would have worked too, provided the characters translated to an odd
address so executing the g (Go) command would raise an address error
exception.

- Michael

Michael J. Hußmann

E-mail: michael@michael-hussmann.de
WWW (personal): http://michael-hussmann.de
WWW (professional): http://digicam-experts.de

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Received on Tue Jun 23 19:57:41 2009

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