Laptop CPUs are custom tailored version of Desktop processors. They normally have the following charecteristics compared to a Desktop processors
1. Low power consumption. It is very much required for being used in a Laptop as you have limited power source. So they have a lower TDP value compared to a similar Desktop processors
2. Low heat generation is another mejor factor as Laptop does not have ventilation like a desktop processors
3. For achieving the above mentioned points Laptop CPUs normally run in lower clock speed and have less resources like less L3 cache compared to a Desktop processors. For example a Nehalem based i7 processor has Tri-Channel memory controller and 8 MB of L3 cache and normally runs beyond 2 GHz speed, even for the chepaest core i7 920, whereas their Notebook based brothers have dual channel memory controller, run slower than the desktop brothers (sub 2 GHz speed) and have less amount of (4 MB or 6 MB) L3 cache.
