Intel 64 and IA-32 Architectures Software Developers Manual Volume 2A, Instruction Set Reference, A-M

Vol. 2 3-171
INSTRUCTION SET REFERENCE, A-M
• Local APIC ID (high byte of EBX) — this number is the 8-bit ID that is assigned to
the local APIC on the processor during power up. This field was introduced in the
Pentium 4 processor.
INPUT EAX = 1: Returns Feature Information in ECX and EDX
When CPUID executes with EAX set to 1, feature information is returned in ECX and
EDX.
• Figure 3-6 and Table 3-15 show encodings for ECX.
• Figure 3-7 and Table 3-16 show encodings for EDX.
For all feature flags, a 1 indicates that the feature is supported. Use Intel to properly
interpret feature flags.
NOTE
Software must confirm that a processor feature is present using
feature flags returned by CPUID prior to using the feature. Software
should not depend on future offerings retaining all features.
Figure 3-6. Extended Feature Information Returned in the ECX Register
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