These keys are sometimes referred to in computer manuals as interrupt keys , since they are often used to interrupt the operation of a malfunctioning program. Bradley originally designed Control-Alt- Escape to trigger a soft reboot without warning or confirmation by the user , but he found it was too easy to bump the left side of the keyboard and reboot the computer accidentally.
Play me online? As computers became ubiquitous, so too, has the jargon. Control-Alt-Delete can also mean "dump," or "do away with. On a PC running DOS or a system that runs in real mode , this keystroke combination is recognized by the keyboard handling code in the BIOS unless the keyboard interrupt has been hooked by some other resident program. The BIOS reacts by invoking a soft aka warm reboot. Under Windows 3. In Windows 3. According to the value of the LocalReboot option in the [Enh] section of system.
As such, it is strongly recommended that, following a process kill in these versions of Windows, any work should be saved in any other applications and Windows should be restarted.
Such damage is much less likely in newer versions of DOS-based Windows because of resource tracking. In Windows 9x, pressing the combination a second time if the process listing has not appeared will display a blue screen from which the user can reboot the system by pressing the combination a third time; other times the system restarts on the second Ctrl-Alt-Delete combination.
This allows the user to over-ride any "stuck" process, since no user-level program is able to define its own response to the Control-Alt-Delete key combination.
However, this functionality does not always work. In Windows NT , and thus on its successors, including Windows , Windows XP , Windows Server , Windows Vista , Windows Server and Windows 7 , this keystroke combination is recognized as a special system-wide "keyboard hook" by the Winlogon process, which in response instructs GINA to perform one of the following tasks:. Windows NT is designed so that, unless system security is already compromised in some other way, only the Winlogon process, a trusted system process, can receive notification of this keystroke combination.
This is because the kernel remembers the process ID of the Winlogon process, and allows only that process to receive the notification. This keystroke combination is thus called the Secure Attention Sequence.
A user pressing Control-Alt-Delete can be sure that it is the operating system specifically the Winlogon process , rather than a third party program that is responding to the key combination see Login spoofing , and that it is therefore safe to enter a password.
It was chosen as the secure attention key in Windows instead of, for example, the System Request key , because on the PC platform no program could reasonably expect to redefine this keystroke combination for its own purposes this is the soft reboot combination in BIOS and DOS. It is also a reliable method for bringing up the Task Manager in Windows and older. All other keystroke combinations could potentially be exclusively tied up by a process that is stuck, but a user process is not able to intercept the Control-Alt-Delete sequence.
The task manager can be however disabled by Windows Group Policies. However, as both the Task Manager and Windows Security have options for shutting down the computer, this operation can still be executed unless the entire system including the Winlogon process is unresponsive. There is no supported method of replacing the login interface as there was in Windows XP , but there is a flexible system for modifying it.
The classic logon screen has been completely removed, replaced with an updated welcome screen, similar to that from Windows XP. In Windows XP, this is done by configuring local security policy. While the default behavior is to have icons for each user, the welcome screen can be configured to prompt for a username and password, though it retains the new UI.
Users can also lock the computer even if fast user switching is enabled. In both cases, the system flushes the page cache , cleanly unmounts all disc volumes, but does not cleanly shut down any running programs and thus does not save any unsaved documents, or the current arrangements of the objects on the Workplace Shell desktop or in any of its open folders. In Linux , this keystroke combination is recognized by the keyboard device driver in the kernel.
In the absence of more specific instructions, which will usually only be during system initialization, the kernel directly initiates a soft reboot in response. More commonly, the kernel will send a signal to the init process, which will perform an administrator-configured task, such as running a script, or displaying an "end current session" box in KDE.
In many Linux distributions, init is configured to switch run levels and to perform a soft reboot in response to the signal. Thus it provides a mechanism for a person with physical access to the keyboard to perform system shut down a task that requires superuser rights to initiate programmatically.
However, Linux systems can be configured to ignore the keystroke combination. Instead of the typical three- to five-year turnaround, Acorn had to be completed in a single year. Turning the machine back on automatically initiated a series of memory tests, which stole valuable time. The tedious tests made the coders want to pull their hair out.
So Bradley created a keyboard shortcut that triggered a system reset without the memory tests. Bradley joined IBM as a programmer in It was an exciting time—computers were starting to become more accessible, and Bradley had a chance to help popularize them.
In September , he became the 12th of 12 engineers picked to work on Acorn. Without this key at the time, users would have been unable to log into the OS. Thankfully, common sense prevailed, eventually, and Microsoft switched to a dual login sequence for secure logins; users either sticking with the old Control-Alt-Delete or the new combination of the Windows key and power button. In any fact, secure login is disabled by default on the new Windows tablets and has to be activated by the administrator.
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