lI hope this helps..
to conserve power, you'll likely find the laptop might be using anywhere from a 3,600, 4,200 or 5,400 RPM hard drive..
pending on the form factor of the hard drive bay and the bios of the mainboard will dictate what the max hdd size you can use..
3.5" max 1.5 tb
2.5" max 500-650gb
1.8" max 200-300gb
if you got money to burn you could go the ssd route for hard drives, though not sure on the hdd capacity in each hard drive format.. you'll have source that info for yourself