Why are file sizes different on XP to Vista Machines??

February 6, 2009 2:44 PM

Why do file sizes vary from Windows XP to Vista?????

I have been transfering Photo files from my old XP desktop to my new Vista Laptop and noticed that the file sizes were sometimes smaller on the Vista machine by 200MB on a 1Gig file. I initially thought that some pictures had been missed, so tried copying them again. Noticing that they were still smaller. I decided to count the actual pictures and there was the same amount!!!
So, how/why is this possible???????

posted by maxmix to computers & internet (16 comments total)

That doesn't sound plausible. How are you determining the file size?

The best way is to right-click on the file and select "properties". That will give you the file size as a true byte-count, and I suspect you'll find that they're the same.

If, indeed, they are not I would suspect a botched transfer which lopped off the end of the image.
posted by Chocolate Pickle at 2:47 PM on February 6

Assuming that Chocolate Pickle is wrong, and the files aren't corrupted...

Different blocksizes would be my guess.
posted by Netzapper at 2:50 PM on February 6

NTFS Compression could be a reason, but 20% seems very unlikely, especially on image files (unless they aren't in a compressed format yet).
posted by starzero at 3:06 PM on February 6

Different blocksizes would be my guess.

Different block sizes only affect the last block in a file, which may not be completely full. It would not produce differences this big.

Is it possible that file compression is turned on by default?
posted by JackFlash at 3:08 PM on February 6

If they are an uncompressed format (older TIF, or BMP) and if the Vista machine has file compression enabled for the drive or directory, then they would crunch some. Depending on what is in the image, they can compress a hell of a lot.

If they are a compressed format (new TIF, JPG, PNG) and compression is enabled, the file sizes would change by only by a very small amount (a percent or two).

A 1G file probably is uncompressed, but if you're moving it to a compressed drive, I'd expect a lot more than 20% compression. 3:1 is pretty typical.
posted by Chocolate Pickle at 3:43 PM on February 6

There's no way that a difference in cluster sizes would result in a 200 megabyte difference, I might mention. NTFS clusters are usually a few kilobytes.
posted by Chocolate Pickle at 3:44 PM on February 6

To determine if a drive is compressed, right click on the drive icon and select "properties". Near the bottom will be a checkbox labelled "Compress this drive to save disk space". If it's checked, the drive is compressed.

To determine if a directory has compression enabled, right click on the directory icon and select properties. Press the "Advanced" button, and then look for that same check box.
posted by Chocolate Pickle at 3:47 PM on February 6

Is your XP box using a FAT32 filesystem? Because that could result in a 200 mb difference.
posted by qxntpqbbbqxl at 3:53 PM on February 6

If the original machine has a big hard drive formatted with FAT16, large amounts of waste are quite likely since the clusters are very large. FAT32 would result in much less waste but there is still room for slop. If the XP partition is also NTFS then I don't have any idea.
posted by chairface at 3:55 PM on February 6

If the original machine has a big hard drive formatted with FAT16, large amounts of waste are quite likely since the clusters are very large. FAT32 would result in much less waste but there is still room for slop.

Again, cluster size will not significantly affect the size of a single file. The maximum loss would be only one cluster (32KB maximum in FAT16, 4KB maximum in FAT32). Cluster size is significant only if you have thousands of small files.
posted by JackFlash at 4:22 PM on February 6

In Windows, if you right click on a file or folder, and click Properties, you should see one line that says "Size" and another that says "Size on disk". The first one is the real size of the file, while the second one is the size considering file cluster issues and compression.

What do these say for your group of files?
posted by Simon Barclay at 5:12 PM on February 6

"I initially thought that some pictures had been missed, so tried copying them again."

I think you are using the word "file" where you mean "folder" or "directory." Is that the case? Because yes, differences in allocation unit sizes between two filesystems, added up across a large number of files in the directory would account for this. But that's only the case if where you are saying "1GB file" you mean "something containing several files that total about 1GB when added together."
posted by majick at 5:25 PM on February 6

What majick said: folders will certainly be differently-sized across different OSes, so that you could easily account for 200MB between XP and Vista. In fact, you can get differences between XP and XP, since (as chairface points out) between NTFS (the kind of filesystem your hard drive uses) and FAT32 (the kind of filesystem your USB drive uses) there are different allocation methods. Hence this strange thing, which I noticed a while ago: if you have a 1GB folder, and you drag it over and copy it to your flash drive, it can suddenly be 800MB.

And since what you said up there didn't make any sense at all, unless maybe your photo files are multi-image TIFFs (which seems a little unlikely), I imagine you are talking about folders rather than files. I mean, how did you go back and count the pictures in a single photo file?
posted by koeselitz at 7:06 PM on February 6

JackFlash: Again, cluster size will not significantly affect the size of a single file. The maximum loss would be only one cluster (32KB maximum in FAT16, 4KB maximum in FAT32). Cluster size is significant only if you have thousands of small files.

But I doubt he's really talking about a single file, since he talks about counting "the actual pictures" in it; he probably does mean folder.
posted by koeselitz at 7:08 PM on February 6

Let's assume he is going from FAT32 on XP to NTFS on Vista. The maximum cluster size for FAT32 is 16KB so on average each file will waste half a cluster or 8KB. At 8KB per file you would need 25,000 files to add up to a 200 MB of savings in Vista. Each file would average 40KB. Could maxmix have a 1GB folder with 25,000 files each about 40KB? And this is ignoring any waste on NTFS in Vista which has a 4KB cluster size.
posted by JackFlash at 9:22 PM on February 6

Also, you may have different settings on the two file browsers. Maybe XP is showing you some hidden temp or system file but vista isnt.
posted by damn dirty ape at 6:26 AM on February 7