Enabling/Disabling the Local APIC
General
On the Pentium®, the processor's Local APIC could not be disabled or enabled by software. Rather, the processor sampled an input pin (on the removal of reset, APIC data line 1 was treated as the APICEN signal) to determine whether to enable or disable the processor's Local APIC.
With the advent of the Pentium® Pro processor, two mechanisms were added that permit software to enable or disable the Local APIC.
Permanently Disabling the Local APIC
Well, not permanently! Refer to Figure 61-9 on page 1511. Immediately following a power-up or reset, the APIC Global Enable/Disable bit in the IA32_APIC_BASE MSR is set to one, enabling the Local APIC. By clearing this bit to zero, software can permanently disable ...
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