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Why is Hard Drive Capacity Different from Advertised Sizes ?

There must have been times when you bought a hard drive or a memory card and realized that the hard drive capacity shown on the package is more than the available space. Ever wondered why the available space was lesser ?

Well, the capacity of the hard drive is the same as what is advertised on the package. The discrepancy in the available space and the advertised space is due to the way the capacity of a hard drive is calculated.

There are methods used to calculate how much information can be stored on the hard disk drive. They are base-2 system and the base-10 system.

In the base-2 system used by the OS, 1GB = 1,073,741,824 bytes. While the base-10 system used by the manufacturing company, 1GB = 1,000,000,000 bytes.

The table below shows the difference for some commonly used drive capacities.

Base 10

Base 2

80 GB 76.3 GB
120 GB 114.4 GB
160 GB 152.6 GB
250 GB 238.4 GB
1000 GB 953.7 GB


Hope this explained why there is a difference between the available and advertised spaces. May you brain rest in peace knowing you weren’t cheated :shock:

Why is Hard Drive Capacity Different from Advertised Sizes ?
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  • jmarzo

    Thank you for clearing that out for me. You’re right, there have been many times that I bought a hard drive that does not have the capacity as advertised. Cheers.

  • sukosaki

    Hmm…I never knew this. I feel ripped off :lol:

  • Jevin

    Yeah, the gap is more remarkable on higher capacity hard drives. This is when you feel ripped off. Great info dude.

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