Gate A20 Option

Common Options : Normal, Fast

Quick Review

This BIOS feature is used to determine the method by which Gate A20 is controlled. The Normal option forces the chipset to use the slow keyboard controller to do the switching. The Fast option, on the other hand, allows the chipset to use its own 0x92 port for faster switching. No candy for guessing which is the recommended setting!

Please note this feature is only important for operating systems that switch a lot between real mode and protected mode. These operating systems include 16-bit operating systems like MS-DOS and 16-bit/32-bit hybrid operating systems like Microsoft Windows 98.

This feature has no effect if the operating system only runs in real mode (no operating system currently in use does that, as far as I know!) or if the operating system operates entirely in protected mode (i.e. Microsoft Windows XP or newer). This is because if A20 mode switching is not required, then it does not matter at all if the switching was done by the slow keyboard controller or the faster 0x92 port.

With all that said and done, the recommended setting for this BIOS feature is still Fast, even with operating systems that don't do much mode switching. Although using the 0x92 port to control Gate A20 has been known to cause spontaneous reboots in certain, very rare instances, there is really no reason why you should keep using the slow keyboard controller to turn A20 or or off.

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