Porchland said:
Can someone give me the quick hit on what "lossless" is, file size comparisons and why it matters?
Most compression schema actually "remove" data from music, graphics, or video, to shrink the file size. In a nutshell, what they try to do is get rid of stuff that humans probably won't notice too much--so what you've got in an AAC is an "approximate" version of your favourite song. The upside is that this "lossy" compression leaves you with small files (good for iPod), the downside is that fine details can be lost.
JPEG is a lossy image compression scheme. So if you look closely at images coming from your digital camera, you can probably see blocky areas where it was decided that the fine details are too unnoticeable to be worried about; JPEG is analogous to AAC. You get small files (good for digital cameras or for downloading over dialup internet) but you lose some of the fine details.
Some comrpession schema don't "remove" any data from music, graphics, or video. In a nutshell (and this is not "technically accurate", but it will illustrate the point), these "lossless" schema look for areas of duplication in a file and figure out a more efficient way of "writing" it in the file. So, for instance, "this exact sound occurs 15 times in the whole song
why write it out 15 times?" and so the compression scheme would rewrite it so that it says "here's a sound, which we'll call X instead of some really long name
every time you see an X, play the whole long sound that X represents". It's like shopping for huge furniture: instead of trying to lug the furniture around the store, you can just bring some barcodes to the cashier--but the real furniture is still there in the back room or wherever. The upside is that you don't lose any details, the downside is that the files are bigger (bad for iPod).
TIFF is a lossless compression scheme for graphics. You can look as closely as you want at a TIFF image but you'll find that it is indistinguishable from a source, uncompressed image (there are exceptions, but they're not important for this discussion). They're also much much larger than JPEGs as a rule; however, assuming Apple Lossless is what it claims to be, TIFF would be an analogous compression scheme.
So, to sum up: Lossy compression = tiny files with less detail, good for portability; Lossless compression = big files with all the detail, good for archiving, professionals, or ____philes. HTH!