Investigate Hard Drive Details
Almost all notebooks today utilize 2.5" SATA hard drives. Whether you're using SATA at its original 1.5 Gb/s speed or second-generation 3.0 Gb/sec is fairly irrelevant because internal disk speeds are the true performance bottleneck, not the interface. Should you decide to install an SSD for superior performance, though, make sure it's on the faster SATA 3 Gb/sec interface.
Keep in mind that some netbook and subnotebook designs are based on 1.8” hard drives, so you can't install a 2.5" upgrade into them. Also, realize that some high-capacity hard drives are thicker than what you can typically install into a laptop’s drive bay. Stay away from drives with 12.5 mm height, because these often won’t fit into most notebooks. Mainstream solutions require the standard z-height of 9.5 mm. Consult your notebook and/or current drive specs to see what you need.