Today you have alot of gimmicks and alot of choices when upgrading and existing computer system or building a new system from scratch. We feel that the best choice for speed, reliability, and performance, is to use a smaller hard disk drive for your main drive, for example perhaps a 40gb to 80gb size drive. Then for your secondary drive, a larger drive which could be as big as 250gb or larger. The simple reason is that the smaller drive will be easier to defragment, and will perform faster with less data stored on it and less room to have to scan to find files. Also, it is a good rule of thumb to store all of your media and other files on the secondary drive, and keep the main drive with windows installed on it, strictly for system files. This setup will be great to ensure that even if there is a problem and you need to reformat your main drive with your OS installed, you will not have to go through trouble of backing up or transferring a large number of files, or even worse yet, risk losing files.