The hard drive provides storage for your computer's programs and frequently used data. Most hard drives today are rated in gigabytes (GB). Not to be confused with RAM, your hard drive is permanent storage for your data. RAM is memory; your hard drive is storage. However, hard drives do serve a function of memory. When Microsoft Windows runs out of RAM to use for programs, it taps into the hard drive to sustain programs. The hard drive then becomes "virtual memory," and while your system will slow considerably when this backup occurs, it prevents your PC from crashing.

One advance in hard drive technology has been the increase in rotational speed. Hard drive performance is measured by two criteria, access time and throughput. Access time refers to how fast data is located and begins to be processed after you execute a command on your PC. Throughput refers to how much data is pushed from one place to another, or processed in a given timeframe. Rotational speed is one component of throughput, and as manufacturers increase it, the speed at which data can be retrieved from, and saved to your system's hard drive will also increase.

You need space for each program that you add to your PC, as well as any data you create. As you add new programs and create new data, it can quickly fill up. Hard drive capacity is like closet space—you can never have too much. While the hard drive capacity included in PCs has rapidly expanded through the years, so has the size of the files that consume this space. High-resolution graphics, audio and video files take up large amounts of storage space. For example, as camcorder interface with PCs continues to grow, you may find yourself editing and storing videos on your computer. Likewise, if you often find yourself downloading and using multimedia applications, as well as the latest 3D-capable gaming software, you'll see your hard drive start to fill up too.