Highest EAX Value
CPUID Function eax=$0
Returned in eax

This function returns the maximum CPUID function that can be called. For example, if the maximum level returned is $2, you can call CPUID function eax=$1 (which returns signature and features information) and eax=$2 (on Intel systems, returns CPU Configuration info), but you cannot call function $3 (Serial number info). It is important to always check this value before calling CPUID functions higher than eax=$0.

Note: Some early (pre Step-B0) Intel P5 processors return $0000_05xx here in error, they only support max EAX level of $0000_0001. Also, these CPUs return a blank vendor string.