The real reason for Ctrl + Alt + Del

What’s the purpose of pressing Control, Alt Delete?

We all know it reboots or locks your box but have you ever wondered why you have to mash this famous key sequence at the login prompt?

Today we’re going to plumb the depths of Microsoft’s rationale and get to the bottom of Ctrl Alt Del.

A little History

There’s a funny story behind Ctrl + Alt + Del (also known as the Three Finger Salute).

You were never supposed to use it.

Let’s whiz through the annals of time way back to 1981 (before I was born).

This was the birth year of MS-DOS and Post It Notes by 3M corporation.  It was also the year IBM kicked off its first PC which used MS-DOS.

A computer guru by the name of David Bradley was spearheading a project for the much anticipated IBM PC.  Bradley noticed that whenever he encountered something that needed testing he had to manually restart the system, which back then, was a laborious process.  It wasted valuable hours Bradley and his team could have been using for coding.  On July 12, 2013 Bradley told Virginia Hughes of Mental Floss magazine that “some days, you’d be rebooting every five minutes as you searched for the problem”.  As a result he needed a faster way to reboot…

And this was the genesis of the worlds most ubiquitous PC shortcut!  The Ctrl + Alt + Del command came into fruition.

The funny thing is that Bradley never intended the key combo to become famous.  He simply whipped up the shortcut to save coding time.  He didn’t fathom that it would become the de-facto way of logging into PCs.

But why that specific key combination?  Why not something like arbitrary like Shift + A + B + C?

If you surveyed the keyboard layout of the early 80’s you would notice that Ctrl, Alt and Del aren’t even in the same zip-code.  The keys were sufficiently far from each other to obviate someone from accidentally restarting a PC.  So Bradley’s keyboard shortcut solved his personal problem: it was a boon for productivity because he could reboot on demand and the keys were sufficiently spaced to avoid accidental reboots

When the IBM PCs shipped in 1981 they never touted this secret shortcut.  In fact, Bradley’s little trick went relatively unnoticed; it was dormant for years.

Image Credit Steve Petrucelli via Flickr

Until the early 90’s

Microsoft Windows entered our lives in 1992 and so did the three-finger salute; however, it was still relatively unknown except by a few eccentric programmers.  It wasn’t until Windows PC started crashing with Blue Screens did people realize that pressing Ctrl + Alt + Del would restart the computer.  That’s because the Blue Screen error message instructed people to press Ctrl + Alt + Del to reboot.

In a sordid twist of events, it was the instability of Windows that made the key trio famous.

Great, but why do we press it to sign on?

Ctrl Alt Del and Security

Pressing Ctrl + Alt + Del to login

It’s all about security baby.

Here’s the thing: malevolent hackers have found ways to impersonate the Windows Login screen.

Hackers have programmed login screens that masqueraded as valid account login screens. Consequently, anyone fooled by this trick would inadvertently submit their login credentials to the duplicitous hacker rather than the harmless PC.  All this happened furtively behind the scenes with the end user completely aloof of the scam.

Ctrl Alt Del is a specific key combination known as a Secure Attention Key, that helps mitigate the problem of false login screens.  The Windows Kernel recognizes that this key sequence belongs to a specific process: Winlogon.exe.  So no other application besides Winlogon.exe can respond to Ctrl Alt Del and therefore; theoretically, it’s a secure sign-on method.

Of course, this postulates that the Windows Kernel itself wasn’t hacked.

The kernel is the crunchy layer of code sandwiched between the CPU and software.

Usually the kernel is protected in a specific portion of memory known as kernel space (while users can load programs and junk up their computers in User Space).  There is a great gorge, a great chasm that separates both spaces – this is to keep one from interfering with the other.

The Bottom Line

If someone monkeyed with the kernel or found a way to compromise the winlogon process that could effectively fool the Secure Attention Key and allow hackers to intercept passwords.  So the moral of the story is that Ctrl Alt Del makes your computer more secure but not indomitable.

So now you know the history behind Ctrl Alt Del and why we have it.  If you learned something new or have some wisdom to share, shoot me a comment below!


Connect with Vonnie on Twitter

Posted in Desktops, Hardware, Laptops, Windows, Windows 10, Windows 7, Windows 8, Windows 8.1, Windows Vista, Windows XP Tagged with:
  • Pingback: The worse passwords of 2014 - fixedByVonnie()

  • michael sherrell

    Sorry, but the Control-ALT-Delete command was WELL KNOWN even in the days of MS-DOS computers, as both the ’86, 286 and 386 computers of the 1980’s – well before Windows 1.0 came into existence. Plenty of computer magazines, Byte, PC-World, PC-Mag, PC-Computing, Info-World and others in that day and age – talked about that command, and provided plenty of other useful tips in those days. On the earliest of computers with only two floppy drives, the C-A-D command was very useful switching between between different sets of program disks and data disks. Or when switching between different environments because of the different autoexec.bat and config.sys settings needed for different programs. The C-A-D command was also very useful when programs became “stuck” – and the computer needed to be re-started. Also plenty of computers had a physical “Reset” button near the power supply which one learned quickly enough to locate. The advent of hard-disk drives with their larger storage in the MS-DOS days simply meant that there were more files to damage, if the files were left “open” during a re-boot cycle. Then Norton Utilities Scan-Disk was really helpful to fix file and disk problems. The real danger of the C-A-D command came about with Windows, because it was a multi-tasking environment, meaning plenty of more files open and likely to be damaged during an sudden “reboot” moment. Frankly folks had to be “stopped” from using C-A-D in a Windows environment. A Scan-disk operation could easily take a few hours to complete on the very large hard drives of those days. Of course all of this kind of stuff is ancient history when the lowest and cheapest tablets, cell-phones and watches of today that have more memory, processing power and storage space than the “muscle-machines” of yesteryear.