Why some CPUs are locked by the frequency multiplier and some do not

Q: I've seen this term lately, and I don't know how to explain it. Why some CPU is doubled frequency lock, some did not answer: CPU main frequency = FSB number x times frequency FSB general to see motherboard support (usually two), also depends on the CPU itself (Intel out of 800 FSB P4). The frequency multiplier is also generally seen in the BIOS settings in the motherboard (someone has previously upgraded the BIOS to increase the frequency of multiples). Unlock the double frequency lock, also not necessarily can "rest assured" overclocking. There is also a problem of stability, overclocking after the biggest sequela is the stability of the lower, often appear panic. There are excessive overclocking will increase the burden of the machine, serious even burn the CPU, so overclocking a little attention! My first machine was PII233 (66x3.5) CPU, overclocking to 266 (66x4) and could not be used. Overclocking to 299 (66x4.5), but no problem. Go up to 333 (66x5), also not! I was very puzzled: Why 299 can be used stably, a low point of 266 can not use it? Later, after many inquiries, only to know the frequency of the whole times can not be used! So far the machine is Win2000 under the sun!