Si no lo haces igual te interesa la entrada de pingdom.com referente a la historia y utilización de la misma.
Como resumen os dejo un fragmento:
How the SysRq key was born
It might not have been the land before time, but it was at least the time before computer users had more than one sickly shade of green (or orange) as the sole color on their screen. That time was 1984, which was the year when the IBM PC/AT was released. For a bit more context, 1984 was one year after the PC/XT had been released. The XT’s keyboard included 83 keys, but the AT had 84. What was the single key that was added? The SysRq key!
Pressing the SysRq key caused the BIOS to execute a special hardware interrupt code. It was originally intended as an aid to running multiple OSs on the PC/AT’s screaming fast 80286 chip (the first one ran at 6 MHz).
Fast forward to modern times after the wildest days of the OS wars are behind us (and sprinkle in a few standards and commonly held best practices), and the SysRq key doesn’t have much use anymore. However, lurking within most PC BIOS, the interrupt that was implemented decades ago is still there. Waiting.
Encontrareis la entrada completa en: Every sysadmin needs a little SysRq magic
Aparte se encuentra una muy información en la Wikipedia System request sobre la mencionada tecla.