File Size Question (CD versus Hard Drive)

June 1, 2009 at 05:26:09
Specs: Windows Vista
If I have a file that's "Size" is 3,764,140 bytes, but the "Size on disk" is 3,764,224 bytes, I understand that there are 84 bytes of wasted space in the last cluster of the file. From my previous knowledge, I understand that there may still be old data written to that "wasted space," even though its not used by the new file.

I noticed that when transferring the file to a CD, it still has the same "Size" (which makes sense), but also the same "Size on disk," as it did when it was on my computer's hard drive.

My question is, when transferring a file to a CD, does the computer only transfer the actual "Size" of the file, and so the reason the CD's "Size on disk" for that file is the same as the computer's "Size on disk" for that file, is because they have similar cluster sizes? Or is it that, when transferring a file to a CD, are you also moving any of the wasted space on the last cluster of the file (that 84 bytes of old data)? If this is not the case, how does the computer recognize to only transfer up to a certain point within the last cluster, and not transfer any old data on that "wasted space?"

I apologize for not being totally brief. But any help would be appreciated.

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June 1, 2009 at 09:24:55
A file will have an End of File (EOF) code at the end of the file that tells the OS that's all there is. The space after that, to the end of the cluster is ignored but the file still 'owns' that space. I'm pretty sure that when you burn that file you're burning everything to the end of the cluster.

My 98 PC has both fat32 and fat16 drives with different size clusters. If I have time later on I'll burn the same file but from different drives and see what file size is reported for each.

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June 1, 2009 at 15:26:20
Thanks DAVEINCAPS. So burning a file from the computer to a CD results in the entire "size on disk" being transferred, whether or not it is data from the file, or old data from the "wasted space" in the last cluster?

I'm a bit confused, because I have several other files that share the same "Size" whether on the computer hard drive or CD, but the size on disk is smaller when on the CD than the computer hard drive. Would that indicate that its not transferring the "wasted space" of the last cluster on the hard drive to the CD? Thanks again for your help.

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June 1, 2009 at 22:31:54
I burned a 99,486,303 byte file to a cd from the fat16 drive which has 32,768 bytes per cluster and the same file on another cd from the fat32 drive with 16,384 bytes per cluster.

The space taken by the file in fat16 was 99,516,416; with fat32 it was 99,500,032. On both cds it took up 99,844,096 bytes.

The wasted space has to be less than the cluster size. For fat16 it was 30,113 bytes. For fat32 it was 13,729. For the cd it was 357,793 bytes, indicating a huge cluster size.

I don't feel inclined to try to figure that out. I don't think it makes sense to speak of the wasted space on a cd in the same terms as with a hard drive. 'CD cluster size' may not even be a real term. Or the wasted space may involve more than the space left over after the EOF. Or multiple files on the cd may make a difference. Also my cd format was CDFS which I understand has been pretty much replaced by UDF (My Nero is 7 or 8 years old) The figures may be different with a UDF format.

But since the cd file was the same size on both cds even though they were burned from sources with different sizes of wasted space I think it's safe to say that the wasted space is not burned to the cd.

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June 2, 2009 at 05:18:18
That makes sense. Thanks a bunch for your help. I appreciate you taking time out to look into that.

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June 2, 2009 at 12:56:56
You're welcome. I couldn't find a reference for CDFS sector size so maybe there's no such thing.

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June 2, 2009 at 20:57:37
Sorry for the bother again; I was reading your earlier post again. Could you explain what you mean when you said "Or the wasted space may involve more than the space left over after the EOF" and also "Or multiple files on the cd may make a difference." Thanks again.

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June 2, 2009 at 21:37:29
I just meant that since it appears the cluster size is different or doesn't apply to cds and since it doesn't seem the wasted space is copied from the hard drive then the wasted space on the cd could come from something else besides the leftover space between the EOF and end of the cluster. I have no reason to believe the examples I gave are the reason, they were only suggestions to consider.

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June 2, 2009 at 21:56:13
Gotcha. That's interesting. I understand it may not be the reason, but out of pure curiosity and speculation, what kinds of things could that wasted space be, if not from the remnants of the last cluster? Sorry if I'm bugging you!

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June 3, 2009 at 15:50:47
It might be information about the file necessary for the OS to properly use it.

If it is wasted space at the end of the file you'd have to assume some kind of cluster thing was going on. Since it's quite a bit more than you'd find on a hard drive maybe the cluster size is dependent on the file size--the larger the file, the larger the cluster thus allowing more wasted space at the end. Experimenting with burning different size files and comparing their wasted space might show something.

But all that is speculation. I just have no idea what's going on with the space.

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