Intel IA-32 User Manual
Page 412
9-38 Vol. 3A
PROCESSOR MANAGEMENT AND INITIALIZATION
Total Size
32
4
Specifies the total size of the microcode update in
bytes. It is the summation of the header size, the
encrypted data size and the size of the optional
extended signature table.
Reserved
36
12
Reserved fields for future expansion
Update Data
48
Data Size
or 2000
Update data
Extended
Signature Count
Data Size +
48
4
Specifies the number of extended signature structures
(Processor Signature[n], processor flags[n] and
checksum[n]) that exist in this microcode update.
Extended
Checksum
Data Size +
52
4
Checksum of update extended processor signature
table. Used to verify the integrity of the extended
processor signature table. Checksum is correct when
the summation of the DWORDs that comprise the
extended processor signature table results in
00000000H.
Reserved
Data Size +
56
12
Reserved fields
Processor
Signature[n]
Data Size +
68 + (n * 12)
4
Extended family, extended model, type, family, model,
and stepping of processor that requires this particular
update revision (e.g., 00000650H). Each microcode
update is designed specifically for a given extended
family, extended model, type, family, model, and
stepping of the processor.
The BIOS uses the processor signature field in
conjunction with the CPUID instruction to determine
whether or not an update is appropriate to load on a
processor. The information encoded within this field
exactly corresponds to the bit representations returned
by the CPUID instruction.
Processor Flags[n]
Data Size +
72 + (n * 12)
4
Platform type information is encoded in the lower 8 bits
of this 4-byte field. Each bit represents a particular
platform type for a given CPUID. The BIOS uses the
processor flags field in conjunction with the platform Id
bits in MSR (17H) to determine whether or not an
update is appropriate to load on a processor. Multiple
bits may be set representing support for multiple
platform IDs.
Table 9-6. Microcode Update Field Definitions (Contd.)
Field Name
Offset
(bytes)
Length
(bytes)
Description