Confused about Apple Lossless and m4a files

John,

if you get info on a file it will tell you what kind it is, in this case Apple lossless. The difference between importing a song this way and regular AAC or MP3 is size. Lossless is roughly 10MB per minute, AAC and MP3 is about 1MB per minute, so a 4 minute song lossless is about 40MB compared to 4MB.
By importing a song as lossless, you don't lose any of the song, whereas AAC and MP3 throw out the stuff you don't really need to hear and enjoy the song, thus the reason it is alot smaller in size. You can increase the bit rate that you import your songs in using AAC or MP3, making them larger, but not by much.

MPEG 4 is more a type of container file. It can hold several kinds of things. In iTunes case, it can hold Apple Lossless audio (which is indeed lossless) or it can hold AAC audio (which is lossy). But in either case, it's still an MPEG 4 file.