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Today is considered normal to use powers of 1000 instead of 1024(SI x base2) on disks capacity(hd, ssh, usb...), even with our operating systems using base2 measures(except Snow Leopard). This makes our brand new "500GB" HD's actually have 465.66 GB on Linux or Windows.

My question is. I know that this is a common practice but, is there any legal statement, IT standard or historical reason to define SI as the storage measurement by the manufacturers? Or it is just business?


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1 Answer 1

up vote 4 down vote accepted
  1. It's technically improper to use k to mean 1024, M -> 1024*1024, and so on. The correct unit for Base2 is ki, Mi, Gi and so on.
  2. There's no basic reason to use Base 2 in HDs. In RAM for instance, it's addressed by physical binary address lines, which means base 2 sizes are "naturally" a matched.
  3. It looks bigger, so Marketing is happy.
  4. You lose some space to the file system (not to "formatting", drives have been permanently formatted from the factory for the last 20+ years). So the number reported would always be lower.
  5. It's very common that the HD isn't exactly the size advertized either. A 2 TB drive from WDC has 2,000,398,934,016 Bytes of storage for example.
Yeah, but it looks like a fight still. Manufacturers insist on using SI, while the majority of the OSes and its tools uses base2 to measure disk space/usage. –  nwildner Apr 3 '13 at 18:27
It's not the OS that's using Base2, it's the file systems, almost all of which have chunk sizes in offsets measured in base2 for efficiency. It's really not a "fight"; it's been this way for a long time. –  Chris S Apr 3 '13 at 18:37

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