Does the 500GB hard drive have a capacity of exactly 500,107,862,016 bytes

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Why does my 500 GB hard disk show up to have exactly 500 107 862 016 Byte?

I'm aware of the GiB vs. GB issue and know that manufacturers of hard drives use 1000 as factor. But I cannot find an explanation for the weird looking number. It is not a power of 2, neither it seems to be any other simple product of numbers (factorization is 2^13 ⨉ 3^4 ⨉ 7 ⨉ 67 ⨉ 1607).

First I thought it is dependent on the manufacturer but than I checked a second drive and it has exactly the same amount of bytes (according to Mac OS X Disk Utility).

So what's the reason for this number?

Best Answer

  • The answer is IDEMA formula, as described in the IDEMA Standard LBA 1-03 specification (specs available here, or direct PDF download).

    LBA counts = (97,696,368) + (1,953,504 * (Advertised Capacity in GBytes – 50))
    LBA counts = (97,696,368) + (1,953,504 * (500 – 50))
    LBA counts = 976,773,168

    Capacity in Bytes = 512 Bytes * LBA counts
    Capacity in Bytes = 500,107,862,016 Bytes

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