[kerby74]

I have an eMac with what is supposed to be an 80 gig HD. In the disc utility the drive shows as a 74.4 gig HD? Is this because the first 5.6 gigs are dedicated to the OS and I really do have 80 gigs with 74.4 available as useable by me?

[drmbb]

Nope, the 80GB is based on base 10 math. That is, 1 kilobyte = 1000 bytes.
The file system is formated in binary - 1 kilobyte =1024 bytes.
A hard disk sold with a capacity of 80GB should format to exactly 74.5058... GB.
The IEEE standards board has actually proposed using:
1 GB = the proper SI prefix, that is 10^9
1 GiB = the binary prefix, that is 2^30
So, 80GB = ~74.5GiB, which is what your file system actually has to work with (minus a tiny overhead for boot sectors and FATs).
Unfortunately, most people don't know that, and most marketing is done using the SI prefix, with the small print caveat that "actual formatted space may be less"
Oops, it's not the IEEE's proposal, but the IEC's.

[sereluna]

No, you have a 74.4GB HD as measured by a computer, which defines a gigabyte as 1,073,741,824 bytes, as opposed to companies which sell you things, whose definition is 1,000,000,000 bytes. This means they can have less space in a HD but pretend it's more afterwards with an approximate calculation. (I can't see any reason why they couldn't make a 85,899,345,920 byte HD and call that 80GB, instead of making an 8,000,000,000 byte HD and calling that 80GB, but that's probably because I've never studied economics.)
Mac OS X is probably taking 1-2GB; if you installed all the extra software that came with it a bit more. That should show up in something like Activity Monitor as 'space used.'
Two other places your space may have gone (but I'm not sure about these, and would like someone to verify/disprove them):
The file system created (I think) when the disk was formatted might not show up as space used, but be part of the main size measurement;
& a disk may not be made to have exactly 8,000,000,000 bytes in the first place, or if they are made to a very precise size there may be some variation between the physical part of the disk that stores a byte, or 8 bits or however it works, and what the electronic side considers to be a byte.
What I want to know is whether a document marked with a size of 4KB (because that seems to be the minimum size) is really that size, or if it just gets labelled so because files are stored in 4KB chunks (I've forgotten what those are called as well) -- i.e. if you moved it to a computer with a different file system, would it show up as a different size (or does the size information get carried with the file?)? If that is the case, is it so in all file systems? I remember reading something about one ASCII character being one byte and proving this by saving the plain text file and checking its size, which surely wouldn't be possible if there was a minimum.
Also, how can there be files of 0KB in size? Are they just listed in a general listing and don't actually exist, or are they really only a couple of bytes in size? (I'm trying to remember where I last saw one to check if they do exist.) That would mess up the idea above, so do applications sometimes put a minimum size on their documents (other than extra information like a history of changes to the document)?

[moose_n_squirrel]

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What I want to know is whether a document marked with a size of 4KB (because that seems to be the minimum size) is really that size, or if it just gets labelled so because files are stored in 4KB chunks (I've forgotten what those are called as well) -- i.e. if you moved it to a computer with a different file system, would it show up as a different size (or does the size information get carried with the file?)? If that is the case, is it so in all file systems?

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Wow, you almost answered your own question with your other questions! Yes there are two sizes. There is the actual size and the size it needs on disk. You can see this in Get Info. The K size is the disk requirement. The bytes in parentheses is the true size. Why two sizes? Disks must be divided into blocks or a minimum size. Imagine that you want to store apples. You can't just put a pile of apples in the warehouse, so you must keep them in boxes. Boxes are like disk blocks. Let's say each box holds 50 apples and you want to store 110 apples. You can't store a partial box so you must store three boxes, two full boxes and one box with 10 apples. So the "storage size" appears to be 150 apples (3 boxes), but the "actual size" is 110 apples. You could use smaller boxes, but it is more work to manage and ship them. That is why disk blocks have a minimum size. You will see many "4K" files that are really much smaller only because 4K happens to be the disk's minimum block size.
You can format your hard disk with different block sizes. Basic disk utilities like Apple's don't show you that option, but advanced ones do.
You asked if the "size" can change if you move to a different file system. You are right. Different file systems can use different block sizes. If the block size is different, the size on disk will appear to change, but remember, the "true size" is never going to change. Try copying a file from a hard drive to a USB flash drive and the size on disk will probably drop. Do a Get Info for both copies of the file and you will see that they will have different "disk sizes" but always the same "true size" (again, the bytes in parentheses). This is like moving the same 110 apples between boxes that hold 10, 100, and 200 apples. It will still be 110 apples but it will appear to take up either 11 boxes, 2 boxes, or 1 box. The reason it is confusing on computers is that we don't see the size of the boxes!

[sereluna]

Thanks moosensquirrel, that was a good explanation. I can't imagine how I missed the smaller size -- I suppose I just don't 'get info' very often on my small text files.

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Wow, you almost answered your own question with your other questions!

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/forums/ubbthreads/images/graemlins/smile.gif. I should learn to organise my paragraphs better, shouldn't I?