Disk Space Myths

Hijacked from Apple's website

Guh… blogging sure requires much more commitment than I’ve anticipated. With so many other things having higher priorities than blogging, I’ve chose to leave it aside for a while. First was the F1 weekend in Malaysia Ｏ(≧∇≦)Ｏ , then I had my Japanese oral exam (which I think I screwed ToT), Japanese written exam up next  ((T.T； )(； T.T))おろおろ･･･ , college finals next week ＼(>o<)／ギャーッ！, pile o work with club and society… and my to-do list goes on… Finally managed to free myself up to write something short.

Just a while ago a friend of mine had some PC problems with a new tread of worm (again, Mac vs. PC, Mac wins!). Manage somewhat to get it fixed but ended up having weird disk space usage readouts, and that, I’ve still yet to figure out. He asked a good question during the diagnostics: He has a 160GB HDD, but Windows shows only 149GB. What gives? The OS took 11GB? Wow…~!

Neh… The answer is: NO, you do have a 160GB hard drive, the OS did not take up that space, and it is still a 160 GIGA-byte hard drive, despite the 149 gigabyte readout… HUH?

(warning: technical data ahead!)

The long, technical reason

Okay okay… Here’s the actual reason why any operating systems will show you less space than advertised on the packaging on the hard drives.

Here’s the catch. Hard drive manufacturer notes the disk space in byte units: for example – 160 giga-bytes means you have 160 billion bytes of storage space. That’s 160,000,000,000 bytes. The giga prefix in metric system means one billion, or 10 to the power of 9. And all those calculations are in decimal. In computing however, things are slightly different. Computing calculations are usually expressed in number base of 2 (binary) instead of 10 (decimal). in order to do conversions, the numbers are expressed also in binary numbering system. The closest thousand that can be expressed in base 2 is 2 to the power of 10: or 1024 in decimal.

In short:

Metric converts bytes to kilobytes by dividing bytes by 1,000

Computers converts bytes to kilobytes by dividing bytes by 1,024

And… the same goes to all increments after that, kilo to mega, and mega to giga, giga to tera

unit = decimal – binary

1 kilo = 1,000 – 1,024

1 mega = 1,000,000 – 1,048,576

1 giga = 1,000,000,000 – 1,073,741,824

1 tera = 1,000,000,000,000 – 1,099,511,627,776

So… In English?

Taking back the 160″GB” hard drive as an example:

Manufacturer logic : 160,000,000,000 / 10 power of 9 (also 1,000,000,000) (GIGA) = 160 GIGA-byte

Computer logic : 160,000,000,000 / 2 power of 30 (also 1,073,741,824)  (giga) = 149.0116119384765625 gigabyte

Basically some marketing genius thinks that by using metric conversions to note disk space, you’ll get a “larger-looking” drive space than it is. And he is not exactly lying to you either. It’s just like expressing weight in KGs rather than pounds, so you’d feel slimmer. They are technically misleading you into believing you have a larger disk space than there actually is. Well… at least the entire storage industry uses the same “error” in expressing storage space, so a bigger number do represent a bigger drive. However do bear in mind that that’s not the exact storage space you are actually getting. And no, the operating system did NOT take up the “lost” disk space, despite what some less-informed sales person might tell you. The difference is caused by the different conversion methods they use to express numbers.