9-30 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

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.

Checksum[n]

Data Size + 76 + 

(n * 12)

4

Used by utility software to decompose a microcode update into 

multiple microcode updates where each of the new updates is 

constructed without the optional Extended Processor Signature 

Table.

To calculate the Checksum, substitute the Primary Processor 

Signature entry and the Processor Flags entry with the 

corresponding Extended Patch entry. Delete the Extended Processor 

Signature Table entries. The Checksum is correct when the 

summation of all DWORDs that comprise the created Extended 

Processor Patch results in 00000000H.

Table 9-8.  Microcode Update Format

31

24

16

8

0

Bytes

Header Version

0

Update Revision

4

Month: 8

Day: 8

Year: 16

8

Processor Signature (CPUID)

12

Re

s: 4

Exte

nde
d

Fa

mily: 8

Exte

nde
d 

Mod
e: 4

Re

se

rv

ed

: 2

Ty

pe

: 2

Fa

mily: 4

Mod
el: 4

St

ep

pin

g: 4

Checksum

16

Loader Revision

20

Processor Flags

24

Reserved (24 bits)

P7

P6

P5

P4

P3

P2

P1

P0

Data Size

28

Total Size

32

Reserved (12 Bytes)

36

Table 9-7.  Microcode Update Field Definitions (Contd.)

Field Name

Offset (bytes)

Length 

(bytes)

Description