System request (often abbreviated SysRq or Sys Req) is a key on personal computer keyboards that has no standard use.[1] Introduced by IBM with the PC/AT, it was intended to be available as a special key to directly invoke low-level operating system functions with no possibility of conflicting with any existing software. A special BIOS routine — software interrupt 0x15, subfunction 0x85[2] — was added to signal the OS when SysRq was pushed or released. Unlike most keys, when it is pressed nothing is stored in the keyboard buffer.