Is the Celeron-M 420 upgradable?

[asiafish]

What is the fastest processor that is pin and clock compatible to the Celeron-M 420 in my 14" R60?

[aaa]

It sounds like a Socket M, so you have plenty of choices; slightly faster Celeron 4xx, Core Duo, and certain Core 2 Duos. There are some incompatible Core 2s as well (that use Socket P). So I think your top speed is more defined by your budget as you can probably put the pricey T7600 Core 2 in there if you want.