x86 - Enable the A20 gate using port 92h only? - Stack Overflow

admin•2025-04-18 13:28:48•questions•阅读3

For enabling the A20 gate, in multiple x86 codebases (including memtest86+ header.S) I've seen the

For enabling the A20 gate, in multiple x86 codebases (including memtest86+ header.S) I've seen the following logic: try BIOS int 15h AX == 2401h. If that fails, do port 92h (Intel fast A20 gate), and (unconditionally) do the keyboard controller method.

Why isn't it enough to try port 92h (after the failure of the BIOS method), and if it succeeds, skip the keyboard controller?

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x86Enable the A20 gate using port 92h onlyStack Overflow