how to decide which cpu to get..

Besides the Ghz, what else do u use to decide which cpu to get? e.g. Mhz, Mb etc

 

The L2 cache, the higher the better (for gaming), watts, 25 watts will run cooler than 35 watts. 45nm runs cooler than 65nm cpu's. Stuff like that..

 

More specifically, I would look for an Intel P-series processor, such as the Core 2 Duo P8600.

 

It depends on what tasks you want to perform with the notebook and what battery life you need.

 

And also if it is the T or the P series.

 

As Phil said, the importance of each factor (raw speed, L2 cache, TDP, etc.) is based on what you are using your computer for. For most games and day-to-day tasks, any Core 2 or Turion with 2.0+ GHz is typically good enough and speed increases do not yield much benefit compared to the cost of the upgreade.

However, if you work with programs that require lots of CPU power (ie. calculations for work, GTA IV, or rendering to name a few) then you want a faster processor w/ higher cache. Your budget will determine how high you can go, though at the really high end you will notice a less and less speed boost.

Finally, if you want an ultraportable (< 13") or require maximum battery life, then select a P series processor.

 

Also note that ultraslim 13" notebooks (e.g. the ThinkPad x301) and many 12.1" and 11.1" models use low voltage or ultra low voltage processors. These are even more efficient, and run cooler, than the P series but come with a moderate performance penalty.

The best of the LV parts is the SL9400 (my CPU) or the recently released SL9600 (2.13GHz, 6MB L2 cache, 45nm, 1066MHz FSB, 17w TDP). The best of the ULV parts is the SU9400, or the recently released SU9600 (1.6GHz, 4MB L2 cache, 45nm, 800MHz FSB, 10w TDP).

 

It is also important to note that ULV processors such as the ones jonlumpkin mentioned are usually BGA mounted to the motherboard. That is a fancy way of saying that the processor is not removable or upgradeable.

If you choose a T or P series processor from Intel they will run the socket P platform, which means the processor is removable and upgradeable.

I wouldnt call much of a power difference between the T and P series. It is claimed as a 10 watt TDP but has anyone done the tests
I have a gut feeling all P and T series chips are 25 watt processors. Intel just markets them in a way they can overprice the "25 watt" ones and sell the "35 watt" ones which probably also have a 25 watt TDP

K-TRON

 

The difference in idle is ~1W. For systems that consume little power (the Dell Latitude E6500 can go as low as 10-11W, from the Latitude/Precision subforum), then 1W can yield a significant battery life benefit. While say a midranged one w/ discrete graphics can consume 30-40W and 1W isn't going to give it more than 5 min. Hence why I mentioned the P processors are most useful in ultraportables (though my example of the E6500 is an exception).