Intel MultiProcessor manual Processor Entry Fields

MultiProcessor Specification

Table 4-4. Processor Entry Fields

	Offset	Length
Field	(in bytes:bits)	(in bits)	Description
ENTRY TYPE	0	8	A value of 0 identifies a processor entry.
LOCAL APIC ID	1	8	The local APIC ID number for the particular
			processor.
LOCAL APIC VERSION #	2	8	Bits 0–7 of the local APIC’s version register.
CPU FLAGS: EN	3:0	1	If zero, this processor is unusable, and the
			operating system should not attempt to access this
			processor.
CPU FLAGS: BP	3:1	1	Set if specified processor is the bootstrap
			processor.
CPU SIGNATURE:
STEPPING	4:0	4	Refer to Table 4-5 for values.
MODEL	4:4	4	Refer to Table 4-5 for values.
FAMILY	5:0	4	Refer to Table 4-5 for values.
FEATURE FLAGS	8	32	The feature definition flags for the processor as
			returned by the CPUID instruction. Refer to
			Table 4-6 for values. If the processor does not
			have a CPUID instruction, the BIOS must assign
			values to FEATURE FLAGS according to the
			features that it detects.

The configuration table is filled in by the BIOS after it executes a CPU identification procedure on each of the processors in the system. Whenever possible, the complete 32-bit CPU signature should be filled with the values returned by the CPUID instruction. The CPU signature includes but is not limited to, the stepping, model, and family fields. If the processor does not have a CPUID instruction, the BIOS must fill these and future reserved fields with information returned by the processor in the EDX register after a processor reset. See the Pentium Processor User’s Manual and Intel Processor Identification with the CPUID Instruction (AP-485) for details on the CPUID instruction.

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