It was used by Microsoft OS/2 1.0 to initiate task switching. IBM added the key to the PC AT, the first PC to use the Intel 80286 chip, which made pre-emptive multitasking practical. IBM felt that a hardware-level interrupt that could be initiated by the user would be handy. Oddly, when IBM later took over OS/2, they didn't make much use of the key. --LDC
Deleted "e.g., the linux kernel can be compiled with "Magic System Request Key support" (without using the BIOS, most likely)" since I'm pretty sure Linux doesn't use the BIOS for this, and any other key could have been chosen instead of SysRq. Put the comment in a separate paragraph, without any implication of it having anything to do with the BIOS. -- SJK
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