# Why is my hard disk smaller than on the box?

Discussion in 'Mac Basics and Help' started by Drum, Jul 26, 2006.

1. ### Drum macrumors newbie

Joined:
Apr 29, 2005
Location:
Southampton, UK
#1
I just installed a new 160Gb Western Digital drive into my Flat Panel iMac G4 (OS 10.4.7) but, before anything at all is installed on it, only 148.93 Gb are available. Does anyone know why? Thanks in advance.

Joined:
Jul 4, 2004
3. ### GimmeSlack12 macrumors 603

Joined:
Apr 29, 2005
Location:
San Francisco
#3
Has to do with the definition of megabyte. A megabyte is considered to be a metric measurement of 1000kB. But in reality a megabyte is an exponential of the integer 2. So intead of having 1000kB = 1mB there is 1024kB = 1mB . As the size of the drive increases there becomes a certain estimation of how much space is available in a drive. So a 160gB drive is created as 160,000,000kB , but that is not equal to 160,000mB, so it is reduced to whatever you end up with.

I know that's a rough explanation but it has to do with the misconception that 1mB = 1000kB. I'm sure I'll get some help on it all.

4. ### ChrisBrightwell macrumors 68020

Joined:
Apr 5, 2004
Location:
Huntsville, AL
#4

According to WD, 1GB = 1,000,000 bytes

According to your OS, 1GB = 1,073,741,824 bytes

Do the math and you'll find your "missing" bytes.

5. ### yippy macrumors 68020

Joined:
Mar 14, 2004
Location:
Chicago, IL
#5
Because there are two different definitions of Gb. One is the scientific version and one is the binary version.

See more here.

6. ### Chundles macrumors G4

Joined:
Jul 4, 2005
#6
A "Kilobyte" should NEVER have been called a "kilobyte."

One kilobyte should equal, and should only ever equal 1000 bytes. But, the folks who made computers in the early days went with kilobyte for their binary level storage whatchamacallits and hence forth a terrible lie was born.

Something is going to have to change, either OS'seses are going to have to report HDD capacity in REAL gigabytes (10^9 bytes) or we're going to have to start using the correct binary prefixes, kibibyte, mebibyte, gibibyte etc.

You haven't been ripped off so don't worry about that, you paid for 160GB which is 160,000,000,000 bytes. It's just that because computers quote binary numbers incorrectly using SI units instead of standard binary units it appears you've lost space but you really haven't.

Sorry if this is a bit forceful, but I've got a few beers and a bottle of red wine under the belt, it's after 4am and I've just got back from a mates marathon SNES Super Mario Bros session so I'm totally wired.

To be honest, it wouldn't be too hard to get a computer to display HDD capacity in GB (as advertised on your HDD box) rather than GiB (as shown in the OS itself).

### Staff Member

Joined:
Sep 2, 2004
Location:
The Centennial State
#7
GimmeSlack12, besides the other problems with your explanation (in reality a Megabyte is not always an exponential of the integer 2), you seem to have your SI prefixes confused. "mB" is not a "Megabyte", it's a "millibyte", which doesn't really exist. SI Prefixes are case-sensitive. m = milli, M = mega.

Similar situation. A "b" is a bit, short for binary digit. A "B" is a byte, which is equal to 8 bits. You meant GB, right?

8. ### Hytower77 macrumors regular

Joined:
Nov 9, 2005
Location:
Some random place outside of Fort Worth, TX
#8
I'm so in envy...nothing like a marathon of any old SNES game...we did that in college with Mario Kart for the 64. Burned many a grade point honing my skills.

9. ### playaj82 macrumors regular

Joined:
Jun 26, 2006
Location:
Kingman, AZ
#9
Don't forget Goldeneye

10. ### Chundles macrumors G4

Joined:
Jul 4, 2005
#10
This is the problem.

1 Kilobyte = 1000 bytes. There is no room for interpretation, "kilo" is an SI prefix relating to units of 10^3. There is not two different meanings for kilobyte, someone decided to use the term incorrectly back when computers were appearing.

1 Kibibyte = 1024 bytes. This is a standard binary prefix relating to units of 2^10. But for some reason the folks who thought all this up decided to incorrectly go with "kilobyte."

KB = 1000 bytes and ONLY 1000 bytes.
KiB = 1024 bytes and ONLY 1024 bytes.

The folks who make the HDDs are correct, it's the computer that is using the wrong terms. You buy a HDD in GB - the computer reports it's space in GiB but CALLS it GB. The numbers are equivalent but the terms are wrong.

Either HDD makers need to start advertising the space in GiB and computers need to start using the terms GiB, MiB, KiB etc or HDD makers can keep using GB etc and computers need to start using the right terms.

Argh!!

It's like if you go to a petrol station and buy 40 litres of petrol but your car shows the numbers in gallons but calls them litres. OK, so the difference isn't so dramatic but you see what I mean.

11. ### someguy macrumors 68020

Joined:
Dec 4, 2005
Location:
Still here.
#11
Question: How come when I take 74.41 (the number my Mac reports the total capacity of my HD to be) and divide it by 1000, then times it by 1024, I only get 76.xx?

80,000,000,000 / 1024 = 78,125,000,000

And yeah, now I'm confused.

12. ### GimmeSlack12 macrumors 603

Joined:
Apr 29, 2005
Location:
San Francisco
#12
Naturally I was trying to punch out an answer as fast as I could so I could be first. And therefore the mistakes. But then again, who's counting? You are apparently and I thank you for correcting my mistakes and making everyone here at MacRumors aware of what I really should have written.
Have a nice day!

### Staff Member

Joined:
Sep 2, 2004
Location:
The Centennial State
#13

I am having a nice day! Thanks.

14. ### Chundles macrumors G4

Joined:
Jul 4, 2005
#14

OK, you have an 80GB HDD.

80,000,000,000 bytes / 1024 = 78125000 Kibibytes

/ 1024 = 76,293.9453125 Mebibytes

/ 1024 = 74.50580596924 Gibibytes

So, your Mac reports 74.41GiB, that means you lose ~0.1GiB to formatting.

Make sense?

15. ### emw macrumors G4

Joined:
Aug 2, 2004
#15
[sarcasm]
It's common practice for packaging manufacturers to use enlarged photos of contents, generally to show more detail but sometimes just because they don't have any other pictures and are too lazy to hire a good prepress guy.

As a result, what you see on the package generally will be sized differently, unless they specifically say "Shown actual size". This tends to be very noticeable on my Grape Nuts cereal boxes.
[/sarcasm]

### Staff Member

Joined:
Jan 20, 2005
#16
Not only that, but there are neither grapes nor nuts to be found in the box. Talk about false advertising...

17. ### rdowns macrumors Penryn

Joined:
Jul 11, 2003
#17

That's why the mirror on my ceiling says 'objects in mirror are closer than they appear".

18. ### Hytower77 macrumors regular

Joined:
Nov 9, 2005
Location:
Some random place outside of Fort Worth, TX
#18
Ah...yes...surly we are not the only two on here that want to re-live the good ol' days...

Damn, i'm getting old...

19. ### swiftaw macrumors 603

Joined:
Jan 31, 2005
Location:
Omaha, NE, USA
#19
Count me in, nothing can beat Goldeneye or Mario Kart on the N64.

20. ### Hytower77 macrumors regular

Joined:
Nov 9, 2005
Location:
Some random place outside of Fort Worth, TX
#20
Thanks, I was beginning to think I was nothing but a spare...

*Looks around room quickly and then thinks to self, damn...nevermind.

21. ### someguy macrumors 68020

Joined:
Dec 4, 2005
Location:
Still here.
#21
Makes perfect sense. I didn't think to convert it that way. Thanks!

Now, what is lost or used up when formatting? Is that ~0.1GiB used to store an allocation table or something? Where does it go?

22. ### Chundles macrumors G4

Joined:
Jul 4, 2005
#22
Yeah, it's used to store all the formatting information, drivers etc.

23. ### Drum thread starter macrumors newbie

Joined:
Apr 29, 2005
Location:
Southampton, UK
#23
Thank you

Thanks to all you kind people for your varied, and occassionally drunken, explanations. Now I understand.

Actually there was no box. It just came in a little anti-static bag. I just said that as a quicker way of explaining

24. ### Sun Baked macrumors G5

Joined:
May 19, 2002
#24
Usually, they blow up the picture on the outside of the box to make you drool.

It is unusual for them to print an actual size picture on the box anyhow.

Understandable that the drive would be smaller than the one pictured on the box.

25. ### Hytower77 macrumors regular

Joined:
Nov 9, 2005
Location:
Some random place outside of Fort Worth, TX
#25
My wife said this about me after we went out a few times...