[GSixZero]

I downloaded a big scientific application that a friend is working on (1.9GB) and when it arrived at my computer it has a different MD5 than the original. The MD5 hashes are totally different.

Is there any way to look at the hashes and determine how different the two files are. If it's only a small amount, I doubt it will matter, but if it's very corrupted I'd probably spend the two days to download it again.

[Mithras]

prebinding in OS X causes executable MD5sums to change.
You can check it with ctool if you want to be careful.

And no, there's no 'distance metric' implied by an MD5 hash -- it is sensitive to minute changes in the original. There are hash functions that are robust under a certain amount of perturbation, but they're obviously not ideal for checking the integrity of executables!

You can read about cryptographic hash functions like MD5 if you're curious.

[GSixZero]

It's a disk image of the appication CD. Does this still apply?

[Chuckit]

Prebinding only happens to applications. Disk images wouldn't be affected by it unless they redid the prebinding before they packaged the app but forgot to update the MD5. I doubt that's the case, but you might check with them to ensure the MD5 is correct on their end if you want to be extra sure it got messed up in transit.

[Mithras]

Disk images themselves have a checksum; can you verify & mount the disk image okay? If so, it should be fine.