How is the CPU frequency given by dmesg obtained?

For example on a PII which is nominally 350 MHz dmesg says:

cpu0: Intel Pentium II (686-class), 350.82 MHz, id 0x652

I'd like to port a program written for linux [1] to NetBSD and it 
gets the CPU speed from /proc/cpuinfo.

Is the same method used for NetBSD/alpha?  I've noticed it almost 
always reports a machine's nominal frequency.


Ray



[1] http://yade.berlios.de/