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Getting an 80286 or 80386 out of 8086/8088 mode to address more memory required access to the A20 address line. Which IBM added to the keyboard controller on th
by rswail 7y ago
Getting an 80286 or 80386 out of 8086/8088 mode to address more memory required access to the A20 address line. Which IBM added to the keyboard controller on the motherboard. Which lead to the A20 hacks necessary to access memory above 1MB (let alone the hacks already in place to access over 640K). Note that this hack has required CPU support up to Intel Haswell which is only 5-6 years ago.
https://en.wikipedia.org/wiki/A20_line https://en.wikipedia.org/wiki/A20_line
- consp 7y agoActually, the hack is to fix the incorrect behavior of the processor in real mode (not lowering line 20 to 0). The fact that it was put into the keyboard controller was probably as it is a simple soc[1] with (in the case of a keyboard controller) about 256 bytes of ram and about 1-4K of rom. Which resources was probably still available to the motherboard designers without complicated logic or additional components. It is not the weirdest fix to imagine. note: modern variant of the keyboard controller can sometimes be flashed which is fun to play around with. [1] https://en.wikipedia.org/wiki/Intel_MCS-48 https://en.wikipedia.org/wiki/Intel_MCS-48