many of the XP series could be unlocked, some by joining the L1 trace and some by shorting 2 processor pins (normally by soldering a wire between the corresponding wires on the back of the socket). Pentium's were unlocked, although i don't think Pentium Pro's were. of course the FX series is and the AMD K6 series were unlocked. apparently the new Core 2 Duo X6800 is unlocked as well.