Hard drives aren’t hard choices

Every computer needs data storage, and though that is something RAM does, the majority of it will go onto your hard drive. There are typically a few different options in the search for a hard drive, but what it really comes down to is how you plan to use your computer.
Basic: If you plan to just have your computer and no peripherals, you may want to opt for the biggest hard drive you can (measured in gigabytes, or terabytes for extra large drives), since all of your files and programs will be stored on the computer. If you don’t plan to have many applications on your computer, and won’t store media on it, then you can opt for a smaller hard drive and save yourself some money. If you can handle a small hard drive but want to it be extra fast and you have the cash, consider going for a solid-state drive,  or flash hard drive.
Advanced: The size of your drive is one thing. If it’s a disk drive, the spin speed is another. Naturally, the faster your hard drive disk is spinning, the quicker information can be gathered from it. So, between a 5400rpm drive and a 7200rpm drive, the second would be faster. If you can handle having only a few larger programs installed on your computer at a time, and plan to keep everything else stored on an external device, you can probably get a quick device with a solid-state drive to keep the computer zippy at all times and still manage to stream high-quality media through a USB connection — some applications may even be able to run from an external hard drive. You’ll also want to pay attention to data transfer bandwidth. The higher, the better.

Source: Seagate.com