Hard Drive capacities

Posted:
edited January 2014
Im curious as to why there can never be a HD that has all of its available space, available. For instance I have a 250gb HD and it only has 233.76 gb of actual capacity, what the hell takes up 16.24 gb's of space??

Posts: 802member
It's how it's calculated. I for consumer purposes a GB is defined as 1000 MB when actually it's a little less if I remember correctly. There's nothing in that space because that 16.24 GB is not really there.
Posts: 648member
Quote:
Originally Posted by maimezvous

It's how it's calculated. I for consumer purposes a GB is defined as 1000 MB when actually it's a little less if I remember correctly. There's nothing in that space because that 16.24 GB is not really there.

Posts: 802member
That's why they say "actual formatted capacity less" as the first point in the small print on all the tech pages on the site.
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It's an issue between computer- and scientific- base counting.

Scientific (metric) bases go by powers of 10. So, deca = 10, kilo (k)= 10^3, mega (M) = 10^6, giga (G) = 10^9, etc.

Computing bases go by powers of 2. kilo = 2^10, mega = 2^20, giga = 2^30.

Instead of 1000 units, kilo in computerese is 1024. Close, but not quite. At small values, this isn't really an issue, but when you get up to hundreds of GBs, it adds up into a highly noticeable amount.

Basically, the computing folks screwed up by adopting something not intended for use in that manner.

What this means, however, is that you'll see 250GB, and it will indeed be 250,000,000,000 bytes... but then the OS/Finder will report it as 234GB, and actually it's wrong. What they mean to say is 234 *computing* GB... which comes out to the 250 *metric* GB just dandy.

There's even a push to fix this by using a new set of prefixes for computing powers of 2. Instead of kilo, it'd be 'kibi' for 'kilo-binary', and the abbreviation would be ki instead of k. Ditto for mebi (Mi) and gibi (Gi).

So... 234GiB = 250GB, the Finder is using the wrong damned prefix is all. No false advertising, just an error in reporting by the Finder. You really are getting 250GB.

Unfortunately, getting everyone in the industry (Apple, Linux distros, MS) to adopt the new prefix isn't trivial. But... as long as you know the difference, it makes sense.