In computer jargon, a killer poke is a method of inducing physical hardware damage on a machine and/or its peripherals by the insertion of invalid values, via e.g. BASICs POKE command, into a memory-mapped control register. The term is typically used to describe a family of fairly well known tricks that can overload the analog electronics in the CRT monitors of computers lacking hardware sanity checking (notable examples being the IBM Portable[1] and Commodore PET; a similar trick is reported having been done to Atari ST displays).
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The PET-specific killer poke is connected to the architecture of that machine's video rasterizer circuits. In early model PETs, writing a certain value to the memory address of a certain I/O register ( POKE 59458,62 [2]) made the machine able to display text on the screen much faster. When the PET range was revamped with updated hardware, it was quickly discovered that performing the old trick on the new hardware led to disastrous behavior by the new video chip, causing it to destroy the PET's integrated CRT monitor.[3]
The TRS-80 Model III had the ability to switch between a 32-character-wide display and a 64-character display. Doing so actuated a relay in the video hardware, and was accomplished by writing to a specific memory-mapped control register. Programs that repeatedly switched between 32 and 64 character modes at high speed (either on purpose or accidentally) could permanently damage the video hardware. While this is not a single "killer poke", it demonstrates a software failure mode that could permanently damage the hardware.
The TRS-80 Color Computer, IBM PCjr, MSX, and BBC Micro from Acorn Computers all contained a built-in relay for controlling an external tape recorder.[4] Toggling the motor control relay in a tight loop would reduce the relay's longevity.
The floppy drive of the Commodore Amiga personal computer could be made to produce noises of various pitches, by making the drive heads move back and forth. A program existed which could play El Cóndor Pasa, more or less correctly, on the Amiga's floppy drive.[5] As some sounds relied on the head assembly hitting the stop, this gradually sent the head out of alignment.
Certain models of LG CD-ROM drives with specific firmware used an abnormal command for "update firmware": the "clear buffer" command usually used on CD-RW drives. Linux uses this command to tell the difference between CD-ROM and CD-RW drives. Most CD-ROM drives dependably return an error for the unsupported CD-RW command, but the faulty drives interpreted it as "Update Firmware", causing them to be bricked.[6]
The Game Boy's LCD screen can be turned off by game software. Doing so outside of the vertical blanking interval can damage the hardware.[7]