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The History And Purpose Of The Sys Rq, PauseBreak, And Scroll Lock Keys

Keyboard Keys

If you are the curious sort, you may have noticed several conspicuous keys towards the right side of your keyboard that don’t really come into play in your daily computing routine. What do they mean, why are they there, and can they be of any use to you?

Today’s post is going to delve into the history and purpose of several lesser known keyboard keys.

SysRq

SysRq

SysRq is an abbreviation for System Request and, on modern keyboards, is often combined with the Print Screen key. To actually invoke SysRq, you need to press Alt+SysRq. Historically, this key was designed to call low-level operating system functions. Pressing this key would make your system’s BIOS generate a special interrupt that made the operating system listen for an event and perform a special function.

On most modern OSes and applications, this key press will be ignored. One notable exception is the open source Linux operating system, where pressing this key enables you to send commands directly to the system’s kernel to help you recover from crashes and debug the OS.

Scroll Lock

Text Only Environment - Scroll Lock

The Scroll Lock key is just a toggle, like both the Caps Lock and Num Lock keys on your keyboard. Its presence is a throw back to older, text-mode environments where screen real estate was limited. In order to quickly navigate a text-only prompt, users could press the Scroll Lock key to enable scrolling of the screen with their keyboard’s arrow keys, instead of moving the cursor one line at a time.

Since modern GUIs utilize mouse wheels and windows with scroll bars, this functionality is gratuitous  and most modern applications will ignore the Scroll Lock key when pressed.

Excel

One popular exception is Microsoft Office Excel. Pressing the Scroll Lock key in this application will enable scrolling the viewing area with the arrow keys without moving the cursor.

Pause/Break

Like the Scroll Lock key, the Pause/Break button was more relevant in the past, when text-based computing environments were the norm. Still functional in the Windows command prompt, this key is used to pause a text-mode program’s output. Press the key a second time to continue the program.

POST

Additionally, the Pause/Break button can often be used to pause the BIOS boot-up process, which can be useful for reading POST (Power On Self Test) information that briefly flashes on the screen.

The Break key (Ctrl+Break) can be utilized to terminate DOS programs.

Source How-To Geek

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