The difference between hard drive and file system size

When specifying a size of a disk, hard drive manufacturers consider 1 KB to be 1,000  bytes, MB (megabyte) to be 1,000,000 bytes, and gigabyte to be 1,000,000,000 bytes.

However, in software, slightly odd measurement units are used.
KB contains 1024 bytes (210),

1 gigabyte (GB) contains 1,073,741,824 bytes.
The difference grows as sizes grow. For a 750GB hard drive, the discrepancy between advertised and useful capacity is about 7%.
In case of a 1TB drive, the discrepancy is close to 10%.
The differences add up quickly, and although one would reasonably expect a RAID 5 array of eight (8x) 2TB hard drives to be 14TB in size, actually it’s only a miserable 12.6TB.

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One Response to The difference between hard drive and file system size

  1. Pingback: Hard drive shows less capacity than expected « Tom, not at home.

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