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Why Partitioning Your Hard Drive Makes Sense
Most PCs come from the factory with a single partition on their hard drive, meaning that it shows up as one drive in the Computer window (as C:, typically). But keeping your data, applications, and operating system on the same partition can be risky because, if something happens to the partition's index file (the file that tells your computer where the various pieces of your data are located), your computer won't be able to boot up off that drive--and even if you boot up with a recovery disc or external drive, you won't be able to access the rest of your data.
One drive, three partitions.
Partitioning your hard drive essentially tells your computer to treat portions of that drive as separate entities. If you keep your system and apps on a partition separate from your data (documents, music, video, and the like), the data will be easier to back up (because your backup utility won't bother to copy the system and apps, which you can reinstall from the discs or redownload from an online source). In addition, you'll be less likely to lose your data in an accident; and if you ever need to reformat and reinstall Windows, you won't have to worry about restoring your data backups.
You can also set up an emergency partition. Suppose that Windows unexpectedly croaks and you don't have your emergency boot disc handy. If you've created a bootable partition that's large enough to contain a stripped-down OS and a handful of diagnostic tools, you can use it to rescue your data and salvage your computer. Some computer manufacturers (Lenovo, for example) supply a built-in emergency partition on some of their PCs, but you can make your own, if your PC lacks one.
Finally, partitioning lets you try out other operating systems--like Linux, for example. Generally, two operating systems can't coexist on the same volume without stepping on one another's toes, so you won't be able to dual-boot Linux or ease into Windows 7 if you're on a single-volume system.