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Scroll Lock (⤓ or ⇳) is a lock key (typically with an associated status light) on most IBM-compatible computer keyboards. The key is infrequently used, and therefore some newer Logitech and laptop keyboards lack Scroll Lock altogether.
The Scroll Lock key was meant to lock all scrolling techniques, and is a remnant from the original IBM PC keyboard, though it is not used by most modern-day software. In the original design, Scroll Lock was intended to modify the behavior of the arrow keys. When the Scroll Lock mode was on, the arrow keys would scroll the contents of a text window instead of moving the cursor. In this usage, Scroll Lock is a toggling lock key like Num Lock or Caps Lock, which have a state that persists after the key is released.
Today, this particular use of Scroll Lock is rarely used. Only very few modern programs still honor this behavior, such as Lotus Notes and Microsoft Excel. Most GUI environments neglect Scroll Lock, which means scrolling must be accomplished with a computer mouse, using means such as scrollbars or scroll wheels. Many common text editors (such as gedit, Notepad++) exhibit similar behaviour when arrow keys are used with control key depressed.
In Multiuser DOS, System Manager and REAL/32, activating Scroll Lock during boot will enter a special diagnostic mode, where the operating system and loaded device drivers will display detailed status and debugging information about themselves and their interaction with the operating system, sometimes up to several screenfuls per loaded driver. Automatic scrolling is suspended for as long as Scroll Lock remains activated.
DR-DOS 7.02 and higher provides a new CONFIG.SYS directive named
SCROLLOCK=ON/OFF to change the Scroll Lock status on the fly. Activating Scroll Lock during boot will enter a DIAG mode as well, wherein some special drivers may display more verbose messages, but in contrast to the situation under the Multiuser DOS family normal DOS drivers do not typically display additional information. The operating system, however, will temporarily suspend any automatic timeouts in CONFIG.SYS trace and single-stepping modes for as long as Scroll Lock is active.
Pressing the Scroll Lock key in the Linux console while text is scrolling through the screen freezes the console output (but not input) — during the duration of the freeze no further text is printed on the screen. When Scroll Lock is pressed again the screen is unfrozen and all text generated during the freeze is printed at once. This allows the user to pause the display and read long messages that scroll through the screen too quickly to read, for example when the system is booting up (provided the keyboard driver has already been loaded). If not configured otherwise, Control+S and Control+Q can be used instead of Scroll Lock, in any terminal in Linux, to freeze and unfreeze the terminal output respectively.
Other uses 
The indicator light is also sometimes used in certain applications, as well as Keyboard Layout Indicator in some Linux distributions because doing so is less likely to cause problems than manipulating other keys/lights.
In some Microsoft Windows versions, a registry setting can be changed to enable a debugging feature that allows the user to manually crash the system, generating a memory dump for analysis. Once set, the user can hold the Ctrl key and tap the Scroll Lock key twice to trigger a BSOD.
Some KVM switches use the Scroll Lock key on the keyboard connected to the switch for selecting between computers. The switching is accomplished by pressing the Scroll Lock key twice followed by a number, or in the case of some 2-port switches, the up and down arrow keys. It is not functional on Lenovo Laptops.
See also 
- "Keyboard - General Discussion". Logitech. 2008-08-28. Retrieved 26 November 2008. "this keyboard does not have a Scroll Lock key"
- IBM: IBM PC User Manual. Page 5-20: "This key is interpreted by appropriate application programs as indicating that the use of the cursor-control keys should cause windowing over the text rather than cursor movement. Pressing the Scroll Lock key a second time reverses the action. The keyboard routine simply records the current shift state of the Scroll Lock key. It is the responsibility of the system or application program to perform the function."
- "Illuminated Keyboard Hack". Kipkay(via Instructables). 2008-05-30. Retrieved 25 July 2011. "Using the Scroll Lock key for illuminating your keyboard"
- 11.JPG (การใช้งาน Ubuntu | SAMUTSAKHON FOUNDATION)
- Keyboard Layout Options, Keyboard Preferences (Desktop User Guide - GNOME Library)
- "Windows feature lets you generate a memory dump file using the keyboard". Microsoft Corporation. Retrieved 25 September 2011.