# 20" imac intel's hard disk capacity: 233 GB. not 250 GB claimed by Apple's specification

Discussion in 'Apple' started by dualline, Mar 18, 2006.

1. ### duallineGuest

Bought a new imac intel 20". Found that the capacity of its built-in
hard disk is not 250 GB but 233 GB. Why?

dualline, Mar 18, 2006

2. ### Tom StillerGuest

This question has been asked and answered at least a dozen times. You
really should check the archives before asking obvious questions.

The difference arises because drive manufacturers use the (correct)
decimal value of 10^9 to represent "giga", while most computer software
uses 2^30 to represent "giga".

The arithmetic is left to the reader.

Tom Stiller, Mar 18, 2006

3. ### Edward DotyGuest

The difference is probably because of the difference in how
manufacturers count. Most companies claim that 250 GB is
250,000,000,000 bytes, while computers count in increments of 1024.
Read the fine print in the specifications and you'll see that they
consider 1 GB to be 1,000,000,000 bytes instead of 1,073,741,824 bytes.

Edward Doty, Mar 18, 2006
4. ### MathueGuest

Not to sound snippish or anything, but..

Why does this question keep having to be answered, YEAR AFTER YEAR?

I recall this coming up over what a 3.5 floppy holds!

<http://en.wikipedia.org/wiki/Megabyte>

From article:

Consumer confusion

Note that computer memory is addressed in base 2, due to its design, so
memory size is always a power of two. It is thus convenient to measure
in binary units. Other computer measurements, like storage hardware
size, data transfer rates, clock speeds, operations per second, and so
on do not have an inherent base, and are measured in the usual decimal
units. Consumers who are (initially) unaware of varying meanings of the
abbreviations often feel shortchanged when they discover the
difference, and claim that manufacturers of drives and data transfer
devices are using the decimal measurements in an intentionally
misleading way to inflate their numbers, though these measurements are
the norm in all fields other than computer memory and storage.
For instance, if a hard drive is said by a vendor to store 140 GB of
data, the disk can store 140?109 bytes. Generally, operating systems
allocate and report disk and files sizes in binary units, and present
them using abbreviations (e.g GB, MB, KB) also used by the decimal
system, so this drive would be reported as "130 GB" (actually 130.36
GiB). Some have even sued these manufacturers for deceptive
advertising, because of the discrepancy. (Another complication is that
the drive wouldn't be able to store files with a total filesize of
130.36 GiB, either, due to filesystem overhead. See Partition
(computing).)

Mathue, Mar 18, 2006
5. ### Steve HixGuest

Because disk drive formatting overhead uses up part of the total disk
capacity. The drive does have that much space, it's just that some of it
is taken up by necessary data beyond your own stuff.

Steve Hix, Mar 18, 2006
6. ### Johan W. ElzengaGuest

No, that's not the reason for this discrepancy. The overhead will not
take up a whopping 17 GB!! The reason is explained in the other answers:
binary versus decimal numbers.

Johan W. Elzenga, Mar 18, 2006
7. ### AlGuest

In my opinion, the confusion stems from advertisers mixing apples and
oranges. In days of yore, a kilobyte was defined as 1028 bits, and so
on. I don't think there was anyone working in the profession who was
confused by it.

Now we have the great unwashed trying to deal with the concept. Most can
only count to ten because they have ten fingers. They never did
understand the concept that number systems can have diffenent bases and
that they are consistent within themselves.

Now that some European standards group has declared that kilo means
1000, the great unwashed think they can apply the prefix kilo to byte
and think it means 1000 bytes. In reality, a kilobyte was, and always
will be 1028 bytes.

Al

Al, Mar 19, 2006
8. ### Tom StillerGuest

I will agree that advertisers make claims that tend to make their
products seem more attractive, but that example doesn't show then mixing
anything.

As far back as I can remember, and probably before computers existed,
the prefix kilo has meant one thousand, as in kilogram, kilometer, etc.

The confusion is sort of akin to measuring television screen sizes on
the diagonal. Not too many people remember that CRTs used to be round
and the diameter was the only measurement that indicated sizes. When
rectangular tubes were produced, the diagonal measurement was introduced
to provide a level of comparison between the old and the new. Round
CRTs have pretty much gone the way of the Dodo, but the diagonal
measurement persists.
As long as all drive manufactures use the same terminology, meaningful
comparisons can be drawn and, except for idle curiosity, the difference
between 1000 and 1024 doesn't matter.
1024

Context is everything. Would you sell 1024 grams of gold for the price
of a kilogram?

Tom Stiller, Mar 19, 2006
9. ### Matthew RussottoGuest

Try "1024 bytes". 1028 bits is 0.125 kilobytes with 50 cents left over.
To be fair, the standards group declared that long before their use in
computers. More recently, they've come up with the abominations
"kibi", "mibi", and "gibi", abbreviated "Ki", "Mi", and "Gi", and they
want the rest of us to use them. Now that's gross; I refuse to use
such gibirish.

Matthew Russotto, Mar 19, 2006
10. ### AlGuest

Ahh, somebody is listening. I bite (pun intended) my tongue.

Al

Al, Mar 19, 2006
11. ### J StewartGuest

Last time I looked that was 1024 (2 to the 10 power) not 1028.

J Stewart, Mar 19, 2006
12. ### William MitchellGuest

The European standards group which declared this was active during the
French Revolution. If you can give an earlier citation for the use of
"kilo" to mean 1024, I'd be interested to see it.

William Mitchell, Mar 20, 2006
13. ### Michael VilainGuest

It's this what's called the "marketing overhead"

Michael Vilain, Mar 20, 2006
14. ### duallineGuest

Actually I had searched it via goole group before I posted it. I now
realize that the question has been asked quite often here with your
information. A FAQ.

In othe words, it IS really a problem to customers in computer
industry, as the others indicated here.

dualline, Mar 20, 2006
15. ### Per RønneGuest

Because most harddisk manufacturers cheat on the bathroom scales ...

In computer science, 233 G = 233 * 2^30 bytes. But the harddisk
companies say it only means 233 * 10^9 bytes. 250*10^9/2^30 = 232.831

In physics, 1 G = 10^9. In the computer industry 2^30.

Per Rønne, Mar 20, 2006
16. ### Per RønneGuest

Consequently, we always used to discriminate between K [meaning 2^10]
and k{ilo} [meaning 1000].

Per Rønne, Mar 20, 2006
17. ### Steve HixGuest

D'oh... I knew that. Brain fault.

(But still, formatting data *does* take up some disk space. Almost
nothing compared to the binary/decimal innumeracy. But still....
/vainattempttosalvagepitifulshredoftattereddignity)
Only so far as marketing takes advantage of the combined
laziness/stupidity of using the same prefixes to describe different
things. "Kilo" *should* refer to 1000, and *shouldn't* be used to
describe 1024.

We're almost too late to disambiguate the issue; it's not clear yet
whether or not the "Gibi" (Giba?) construction will actually see

Steve Hix, Mar 20, 2006
18. ### Steve HixGuest

So we try to plug the hole in the dike with GiB...

Steve Hix, Mar 20, 2006
19. ### Per RønneGuest

That's the reason for choosing K and k as examples - I perfectly knows
what you wrote.
.

Per Rønne, Mar 21, 2006
20. ### Jd LyallGuest

I think that "European standards group" made that decision a few
thousand years ago. Kilo, does in fact mean one thousand. Probably long
before western (or any?) mathematicians comprehended the utility of base
2 mathematics. Base 60 was used WAAY long ago tho.

Jd Lyall, Mar 27, 2006