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For fun and laziness, I've got 20 entries in my GRUB2 menu. To get to the bottom one quickly, I tap down-arrow a couple of times during the GRUB loading screen. I can press the key 15 times (+/- 1, don't remember) -- the next press, GRUB beeps and the menu choice isn't affected.

Why would someone put the limit at 2^4 on a 64-bit processor? Is it even a GRUB problem, or is it caused by keyboard queuing?

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up vote 3 down vote accepted

Do you mean you press the key 15 times before Grub has time to process the first press? If so, that's the BIOS buffering the key presses. The BIOS probably has a fixed-size buffer whose size probably hasn't changed in >30 years. (The API hasn't changed, the hardware has to some extent but for the BIOS's sake it'll emulate older hardware, and there isn't any demand for fancier behavior, so BIOS writers don't bother.)

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Most any bootloader relies heavily on the PC BIOS to control hardware. GRUB2 is no different and it relies on the BIOS to monitor the keyboard and keep track of keystrokes. Your seeing the limit of your BIOSes keyboard buffer. I guess they decided if no one is asking for key strokes then there's no point to keeping more than 16 which I think is reasonable. Until GRUB starting asking for keystrokes, the BIOS will not record more and instead beep at you.

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