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:

Alfred

Alfred is a Pilot & Tech blogger from India. Currently he is pursuing a career in aviation.

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4 Comments

April 28, 2008 at 11:53 am

kaushik

Perhaps you would like to read this

1 Gigabyte is Not Equal to 1024 Megabytes
January 8, 2008 at 9:29 am

Jevin

Yeah, the gap is more remarkable on higher capacity hard drives. This is when you feel ripped off. Great info dude.
December 28, 2007 at 9:17 am

sukosaki

Hmm…I never knew this. I feel ripped off :lol:
December 28, 2007 at 7:13 am

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.

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