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Q. I'm using Windows XP. When I right-click a file and choose Properties, it shows two different sizes, labeled "size" and "size on disk." Which one should I use when I'm trying to figure out the actual size of a fileāand why are there two sizes shown? I'm confused.
A. Your question requires a semi-technical answer, so I'll do my best to respond in a way that won't cause your eyes to glaze over. Caution: Do not continue reading if you are operating heavy machinery! Okay, here goes: Hard drives save data in what are called clusters, and cluster sizes vary. A cluster is comprised of disk sectors, and it's the sectors that you tidy up when you run Disk Defragmenter. When you run Scan Disk, part of what you're checking is the integrity of your clusters. And nobody likes a person with untrustworthy clusters.
For the sake of our example, let's say your hard drive's clusters are 10 kilobytes each in size. And let's say you need to save an 8-kilobyte file. Because clusters aren't shared, your 8-kilobyte file is going to use the entire 10-kilobyte cluster, making it unavailable for other files. So the "size on disk" figure refers to how much space the one file is consuming on your hard drive, based on utilized clusters. If you want to know what the actual data size of the file is, then you'll want to refer to the "size" number. (Anybody still awake?)
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