[inforoots] 3 Key PC Reset Sequesnces

[Evan Koblentz]

Here's an article I published on Feb. 2, 2004.  Keep in mind that the my
target audience was computer collectors and hobbyists:
 
 
It was either Ctrl-Alt-Del, or shorting two contacts with a screwdriver.
 
David Bradley chose the former method for doing a warm reboot of IBM's
original PC, and he did a lot more.
 
"Early in '81, we were dealing with prototype software, prototype hardware,
and as you would attempt to try things out it would hang up.  We needed a
faster way than turning the power off, waiting a moment, turning it back on.
I stuffed a specific value in a location in memory and jumped to the reset
vector," he explained, in an interview with Computer Collector today.
 
But why'd he pick those three keys?  "It's not as if somebody said 'we need
you to pick out three keys to reboot the machine'," he explained.  "Two of
them had to be shift keys," since most of the IBM PC's memory was already
spoken for.  "I'm already tracking whether these four shift keys are up or
down.  So I picked Ctrl and Alt as the two newest, least used keys.
Ctrl-Alt-Delete has a better mnemonic feel than Ctrl-Alt-Plus," he said.
"The systems we had in the lab, it was easy to reset them, you just struck a
screwdriver across a couple of contacts."
 
For Bradley, now 55, it was hardly the highlight of his career.  He
graduated in 1971 from the University of Dayton (Ohio), the same year as
Intel released the 4004 chip, and received his Ph.D. from Purdue in 1975,
the year of MITS' Altair kit.  "The first computer I ever used would have
been a [IBM] 360," he said.  He joined IBM in June 1975 and worked on the
System/23 Datamaster in 1978 - IBM's first computer with a non-IBM
processor.  For the IBM PC, he wrote the entire BIOS.  "I wrote virtually
all of the code that's there with the exception of the cassette and the
power-on self-test," he said.
 
Had they known it'd last 20 years, some things would have been done
differently.  For example, "The interrupts on what's now called the ISA bus
are positive-edge triggered and we should have made them negative.  The
consequence of that decision is it was impossible to share interrupts," he
said.
 
Bradley said he doesn't maintain a personal collection, but has owned
various significant machines over the years.  "For a while I had one of the
original lab-built IBM PCs, but unfortunately in a move, I have no idea what
happened to it.  I may still have an old Timex Sinclair 1000 sitting around
somewhere."
 
 

-----Original Message-----
From: Peter Capek [mailto:capek at ieee.org] 
Sent: Saturday, April 26, 2008 3:52 PM
To: Open Discussion about the history of the Information Age
Subject: Re: [inforoots] 3 Key PC Reset Sequesnces


As I recall, the inventor of this was (Dr) Dave Bradley, then of IBM.   He
spoke about it at the time of the 25th anniversary of the 
PC (or was it the 20th?) a few years ago.   I think it was during a panel
discussion at the Tech Museum in SJ.

If you really are asking about the impetus, it was that they wanted a way
(short of powering down and back up) a way to reset the state of a system
under development when it got itself tied into a knot.  But the 3-keyed
combination was, as someone else has said, a way of
making it difficult to do it by accident.   I'm sure that the video of Dave
talking about this is on the web somewhere, probably in Youtube, but I can't
find it with a quick search.

       Peter Capek


On Sat, Apr 26, 2008 at 1:34 PM, Bill Selmeier <bills at right-net.com> wrote:


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=======================================
We've added a new member to this list who knows the answer to the question
What was the impetus for Ctl-Alt-Del and why that particular combination was
chosen to reset PC code?  I'm interested in the trade-offs.

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