Yesterday, I got tired of coding and decided to look some sites about CPUs and other interesting things... I found the site
http://www.rcollins.org/secrets/, which shows CPUs secrets and bugs, and
http://www.rcollins.org/secrets/opcodes/, which shows undocumented opcodes. The site is old and isn't updated (looking
http://www.rcollins.org/Errata/ErrataSeries.html, the last article is from February 1998, and there are many 404 errors on the links), but has a interesting article about A20.
Here, it shows that resseting a computer with A20 disabled may jump to unknown code, which will probably stop the CPU (triple-fault again and again...). I belive this doesn't happen nowadays (my 32-bit CPU resets normally with A20 disabled), but it's a nice information to keep OS's compatible with older CPUs and avoid crashes. I didn't know that, and I was testing some CPU features (Long Mode, for example) before enabling A20. If the CPU doesn't support Long Mode, I would show a error message and triple-fault. On older computers, that would crash the computer. Other developers can be doing the same error.
Do you think it's a good info for the wiki article? If yes, could you add it (my english isn't very good)?