Glance at your keyboard and chances are you’ll see a few keys you never use near the top-right corner: Sys Rq, Scroll Lock, and Pause / Break. Have you ever wondered what those keys are for?
While these keys have been removed from some computer keyboards today, they’re still a common sight — even on new keyboards.
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The SysRq key (sometimes Sys Req) is an abbreviation for System Request. These days, keyboards generally combine the SysRq key with the Print Screen (or Prt Scr) key. To actually invoke the System Request key, you’d need to press Alt+SysRq.
This key was meant for invoking low-level operating system functions. it behaves differently from other keys on your keyboard – when you press this key, your computer’s BIOS generates a special interrupt that tells the operating system the key was pressed. The operating system can listen for the event and do something special.
These days, most operating systems and programs will simply ignore this key-press event. One notable exception is Linux, where the “Magic SysRq key” can send commands directly to the Linux kernel to help recover from crashes and debug the operating system.
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Scroll Lock is a toggle, just like Caps Lock and Num Lock – on some keyboards, Scroll Lock may also have a dedicated light.
Scroll Lock was designed for older, text-mode environments, which had a small amount of available screen space. Pressing the arrow keys normally moved the text-entry cursor around, but people wanted a way to scroll up and down through the contents of a text screen.
When Scroll Lock was enabled, the arrow keys would scroll the contents of the screen instead of moving the cursor.
With modern graphical environments that include scroll bars and mouse wheels, this behavior is no longer necessary – in fact, most programs will ignore the Scroll Lock key entirely.
One notable program that continues to obey Scroll Lock is Microsoft Excel. When Scroll Lock is enabled in Excel, pressing the arrow keys will scroll the viewing area without moving the cursor.
Pause / Break
The Pause and Break keys were used in DOS and still function in the Command Prompt today.
The Pause key is designed to pause a text-mode program’s output – it still works in the Command Prompt window on Windows. When you press Pause, the output scrolling down your screen will stop. Depending on how the program is written, this may also pause the program’s execution. Press another key after pausing and the program will continue.
The Pause key can also pause many computers during the BIOS boot-up process. This can allow you to read BIOS POST (power-on self-test) messages that flash on your screen for a short time.
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The Break key can be used to end DOS applications – pressing Ctrl+Break terminates a DOS application. This shortcut functions similarly to Ctrl+C, which is also used to terminate applications in command-line environments.
These keys are old and not commonly used – if you wondered who was using them, the answer is very few people. With the exception of the Scroll Lock key in Microsoft Excel, there’s very little the average person can do with these keys. In fact, it’s surprising that they’re still so common on keyboards today.
This post was written by Chris Hoffman and was first posted to www.howtogeek.com
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