What exactly is the difference between an md5 and an iso. disadvantages and advantages of both?
An MD5 is an 128bit hash value (such as
49f68a5c8493ec2c0bf489821c21fc3b), wheras an ISO file is a "disk image" - effectively a file containing the same data as a physical disk would. You're comparing the sticker on an apple to an orange, here - the two are not related. You may find ISO files that come with an MD5, as each file has a unique hash (Well, unique enough that it can be used for verification), and so a corrupt download (though not one tampered with--that is, it's valid to use MD5 for integrity checks, but not validation or security) will not return the same hash as the original file.
When you download disk images like iso there is *.md5 included!
The md5 is a hash of the related iso in order to verify its integrity! So when you download a disk image you compute
$ md5 image.iso and compare what you get with the given md5 hash! If they match then your disk image probably doesn't have any errors!