Unlike what many people believe, most notebook CPUs aren’t soldered on the motherboard thus making a replacement or upgrade impossible, they can be replaced or upgraded relatively easy. One thing to keep in mind though is that not all notebooks come with proper documentation on how to disassemble and properly configure it for a new processor. Most recent notebook motherboards behave similar to a desktop motherboard so it will autoconfigure a CPUs clockspeed and core voltage to match the new CPU, but depending on your notebook’s make and model this may not be the case. Furthermore the cooling requirements for the new CPU should be a match for the cooling solution used in the notebook. It simply doesn’t make sense to plug in a Mobile Pentium III at 1GHz if your notebook’s cooling solution can only cope with 700MHz, it’ll quickly overheat and start to display the dreaded BSODs or worse.
Fig 5. Standard cooling solution for notebooks, a aluminum heatsink with a heat-pipe for better heat transfer.
In actuality the 1GHz Mobile Pentium III might not be what you’re looking for after all. Sure, it offers great performance, but it’ll drain your battery faster than anything else. We’d opt going for one of the low-voltage versions of Intel’s Mobile Pentium III, and rather go with the 750MHz clockspeed version right away. These low-voltage versions offer a big reduction in power drain as the core-voltage of these CPUs is much lower than the other models. And as for performance, 750MHz is fast enough for almost anything, those 250MHz extra the 1GHz buys you will go unused most of the time. And quite frankly, I’d rather trade a few MHz for battery life, as a drained battery will cut into my productivity much more than a CPU not running at 1GHz.
Fig 6. A 750MHz Low-Voltage Mobile Pentium III CPU, offers a good combination of performance and low power drain.
If you happen to have a notebook equipped with an Intel Mobile Celeron you’re also much better off with upgrading it to a Mobile Pentium III. Not so much because of the performance but simply because of the SpeedStep feature included with the Mobile Pentium III. It basically lowers the clockspeed and core-voltage when running off of batteries, and issues a halt instruction when the CPU is not in use, thus putting the brakes on the power drain. A Mobile Celeron doesn’t have that feature and will be running at its full clockspeed all the time, regardless of what power the notebook runs off of, or whether you’re actually doing work or not.
More information about Intel's Mobile CPUs can be found here: Intel Mobile CPUs