In the latter part of 1980, IBM began working
on a project known as Acorn.
Project Acorn would be IBM's new attempt to create a personal computer.
A desktop PC that was anticipated to sell a modest 241,000 units over it's first five
years.
Of the 12 engineers chosen to complete this project was David Bradley.
David had worked for IBM as a programmer since 1975, and in 1978 had worked on the System
/23 Datamaster computer that would launch in July 1981, but would ultimately disappear
into obscurity against the Acorn project.
Unlike the Datamaster, Acorn needed to be completed within a year to compete with rivals
from Apple and RadioShack to name a few.
Of course, development of a new machine meant many bugs, and therefore many system reboots.
With the limited time available, performing a cold boot for every glitch was consuming
more time than they'd like, with the machine running through the POST, memory and start-up
tests on each occurrence.
To solve this infuriating problem, one of the tasks on David's checklist was to create
a quicker solution, a shortcut, which didn't involve the PC restarting from a powerless
state and therefore bypassing POST.
This shortcut would come in the form of a key combination.
Given the IBM PC keyboard is wired to IRQ 1 within the PC's architecture, this made
perfect sense.
When a signal is received through this hardware interrupt it becomes the CPU's highest priority
and therefore any reset request should be issued straight away.
Scanning the keyboard, David chose a combination of keys that were unlikely to accidentally
be pressed simultaneously, given that no wants to reset their computer accidentally.
After first considering CTRL-ALT-ESC, but realising it was too easy to mash the left
side of the keyboard and activate it, he reasoned it would need to require 2 hands to execute
and involve keys which could be pressed at the same time without sending characters to
the computer.
For this he chose Ctrl-Alt and Delete.
It reportedly took David 10 minutes to implement before moving onto the next task, and that
was that.
It's original intention was purely to assist the team in their development and never envisaged
as an end user feature.
However it remained, coded into the IBM BIOS, ready to be executed when required.
Project Acorn would then be released to huge success as the IBM 5150, leaving the keyboard
command enshrined in circuitry.
For IBM PC compatible users throughout the 80s and early 90s, this was a useful and much
used feature among those in the know, although it wasn't hugely documented until the arrival
of Windows 3.0.
As a MS-DOS user, this combination also seemed to fit well among other commands built into
software, such as CTRL-BREAK and CTRL-C that could intervene the execution of programs
under Microsoft DOS.
The latter having descended from the TOPS-10 Operating System by Digital Equipment Corporation.
For any x86 computer running in REAL mode - which even computers today start up in - CTRL-ALT-DELETE
is a direct path to the BIOS which instigates the reset command.
It's why when you boot even a modern computer, it will still cause a reboot, until the operating
system takes over and activates protected mode.
When Intel's 80286 processor was released in 1982, it allowed a new mode of operation,
known as protected mode.
This was improved upon for the 386 processor in 1985 and when Windows 3 was released on
May 22nd 1990, it made use of this new protected environment to provide virtual memory, paging
and safe multitasking.
This mode could also circumvent the BIOS, and so with this in mind, Microsoft re-purposed
the CTRL-ALT-DEL key combination to instigate a blue screen that could kill a problematic
application without having to perform a complete reboot.
However, if this was unsatisfactory, the user could press those same keys again to initiate
a BIOS interrupt call a reboot as if they were still in DOS.
Windows 95 took this a step further by halting the entire system and displaying the task
manager which could be used to terminate whichever application you desired.
System errors would also trigger the blue screen (of death) and allow you to reset using
the key combination.
Since then, the key combination has been used in pretty much the same way, whilst also allowing
us to log onto our operating system in the first place.
When Windows NT appeared in 1993, designed for server and serious business use, it required
a Secure Attention Key, so users knew they weren't entering their password into a spoof
program.
Pressing CTRL-ALT-DEL was a call directly to the operating system, so if a program was
pretending to be the NT logon screen, pressing this would bring up NT's equivalent to the
task manager, and you'd know it was a fake.
However, a true NT login screen will simply allow you to enter your password, and know
you're safe.
And so like that, CTRL-ALT-DEL had found it's further purpose in life, not only allowing
us to reboot, but to login to our new operating systems in the first place.
In 2013 Bill Gates, having really pushed the "Three Finger Salute" to become the famous
combination it is...
"I can't take all the credit.
I may have invented it, but it was Bill who made it famous"
*laughter*
"I mean, with the Windows NT logon screen!"
...seemed to complain that he tried to get IBM to add a dedicated SAK key before NT came
out.
However, given most PC's weren't even made by IBM at this point, it seems a little odd.
Especially given that it's Microsoft who really had the power to get keys added to a keyboard,
with Windows 95 keys appearing from the mid 90s onwards.
Again, more recently he mentioned that he'd have made the combination a single button
from the outset, but then we're just back to the same issues Bradley had with accidental
restarts.
In any case, CTRL-ALT-DEL is thanks to the IBM engineer David Bradley who followed a
jam packed career at IBM before retiring in 2004.
So whether you like CTRL-ALT-DELETE or not, that's what we've got.
I personally wouldn't change it for the world.