Erased hard drive not showing full capacity

I have just finished erasing my Hard drive to sell my iMac, however it is a 250 GB Hard drive in there, but it only shows 230 gig free? why is this when it has wiped the whole drive and operating system??

Cheers

Bussta said:

I have just finished erasing my Hard drive to sell my iMac, however it is a 250 GB Hard drive in there, but it only shows 230 gig free? why is this when it has wiped the whole drive and operating system??

Cheers

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The formatted size of a drive is always less than the manufacturers branding. I'd expect a 250gb drive to have approx 232gb free once formatted which is what you're seeing.

The manufacturers quoted size always differs from the way the OS calculates it.

I'm sure some here will know the correct formula to work it out.

When you buy a "500 Gigabyte" hard drive, the vendor defines it using the decimal powers of ten definition of the "Giga" prefix.
500 * 109 bytes = 500,000,000,000 = 500 Gigabytes
But the operating system determines the size of the drive using the computer's binary powers of two definition of the "Giga" prefix:
465 * 230 bytes = 499,289,948,160 = 465 Gigabytes