documentation for sysctl MIB

[Ole]

Hello maillist, 

I have to small question
- Where i can get documentation for description some "base" sysctl variables?
- And, what the diffrence between 
sysctl hw.machine hw.machine_arch
?

For example, i extract i386 installation, but my hardware is EM64T  and 
supporting AMD64 distribution correctly. Both variable get i386 value. One of 
them must be amd64?

Thanks for your time