The Brand string is a new extension to the CPUID instruction implemented in some Intel IA-32
processors, including the Pentium 4 processor. Using the brand string feature, future IA-32
architecture based processors will return their ASCII brand identification string and maximum
operating frequency via an extended CPUID instruction. Note that the frequency returned is the
maximum operating frequency that the processor has been qualified for and not the current
operating frequency of the processor.
When CPUID is executed with EAX set to the values listed in Table 1, the processor will return
an ASCII brand string in the general-purpose registers as detailed in Table 1.
The brand/frequency string is defined to be 48 characters long, 47 bytes will contain characters
and the 48th byte is defined to be NULL (0). A processor may return less than the 47 ASCII
characters as long as the string is null terminated and the processor returns valid data when
CPUID is executed with EAX = 80000002h, 80000003h and 80000004h.
The cpuid3a.asm program shows how software forms the brand string (see Example 1). To
determine if the brand string is supported on a processor, software must follow the step below:
1. Execute the CPUID instruction with EAX=80000000h
2. If ((returned value in EAX) > 80000000h) then the processor supports the extended CPUID
functions and EAX contains the largest extended function supported.
3. The processor brand string feature is supported if EAX >= 80000004h