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I have created a new Primary partition on XP. After I formatted the drive, I can see the hard disk space isn't 100% available. A small amount of disk space is used already and the partition was created as NTFS.

I hope someone would have idea what's going on? I have attached the link to the screen shot below

http://picasaweb.google.com.au/lh/photo/tbhZ5dn0sMxLV3PqTeCs3g?feat=directlink

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migrated from stackoverflow.com Jul 20 '09 at 11:13

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Should be on superuser.com –  scheibk Jul 20 '09 at 11:11
    
Once that site goes out of beta and is actually accessible, anyway. –  Michael Borgwardt Jul 20 '09 at 11:13

2 Answers 2

There'll be a small amount of disk space reserved for system purposes such as indexing info or deleted items - these are likely to take up small space even if you don't have anything on the drive yet.

I wouldn't worry too much, it's only about 0.04% of the disk.

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Actually, NTFS will use up to 12% of the disk for the MFT & caching... but it will relinquish some of that back as the disk fills up. –  moobaa Jul 20 '09 at 12:40

There are two reasons that the available disk space is less than you may expect:

Some of the disk space is always used to keep track of the data. A FAT file system for example uses a file allocation table to link file clusters together into files. The file allocation table is reserved for all the disk space from start, so it uses a certain small percentage of the total space.

Disk space is either calcualted using scientific prefixes or binary prefixes. A kilybyte is 1000 bytes while a kibibyte is 1024 byte. Hard drive space is always specified using scientific prefixes, so a 1 TB disk is around 1000000000000 bytes. The operating system always shows the disk space using binary prefixes, so the disk shows up as only 931 mebibyte. To further add to the confusion, most systems still use the scientific prefixes even if they calculate the numbers using binary prefixes, so the systems says 931 MB when it really means 931 MiB.

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