Maciej W. Rozycki wrote:

John Sigler wrote:

quoted

As far as I understand, the Local APIC was integrated directly to the CPU
12-15 years ago. Why would a BIOS implementor choose to disable it?

Because they are lazy/incapable/out-of-time/select-your-favourite-excuse.
For the chip to work you have to provide some minimal support in the
firmware, in particular for the trickier paths of execution in the system
management mode.  The system still works with the Local APIC disabled, so
why bother?

The motherboard manufacturer (well, their level 1 support, anyway) told 
me I could "safely enable the LAPIC". If it is safe to enable the LAPIC, 
then why are they disabling it in the BIOS? (They weren't able to tell 
me whether their BIOS triggers SMIs or not...)

Is this a "either works or doesn't" situation where hell should break 
loose if I try to enable the LAPIC and it's not supported by the 
motherboard, or is this a "you will silently lose data at the worst 
possible time" situation?

quoted

(And what does it mean to "disable" the LAPIC?)

The LINT0 and LINT1 inputs of the APIC are routed straight to the INT and
NMI inputs of the CPU respectively and the rest of the APIC logic becomes
inactive (tri-stated, etc.).

If that were the case, then I could not enable the LAPIC and have NMIs 
work, right?

Regards.