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Why are hard drives never as large as advertised?

I just discovered a minor curiosity in My Computer.
My Computer shows that my HDD is partitioned into 3 drives:

  • C is 238 GB (Operating system)
  • D is 332 GB (Data)
  • R is 24.9 GB (Recovery)

As you can see, these partitions only add up to 594.9 GB. However, my computer was advertised as having a 640 GB HDD. Furthermore, in the System Information menu, under Components/Storage/Disks, is lists the disk size as 596.17 GB.

Does anyone understand why this is? Any help is much appreciated. Thanks!

I'm using Windows 7 64-Bit

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marked as duplicate by Karan, Simon Sheehan, ChrisF, Mokubai, Dennis Dec 31 '12 at 1:12

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1 Answer 1

It is called marketing :)

HD manufacturers measure 1GB as 1000MB and Microsoft measures 1GB as 1024MB. Hence the reason you are seeing a 640GB drive as 596GB.

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Sort of. Actually, 1 GB is 1000000000 bytes, while 1 GiB is 1073741824 bytes. Microsoft is really at fault here, labeling GiBs as GBs. Linux (that includes Mac OS), uses the proper prefixes. –  Dennis Dec 30 '12 at 3:36

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