Uncompressed CD Audio runs about 10 MB per minute, so if all of the discs were full-up (80 minutes), and you encoded them uncompressed, you'd need (1500 * 80 minutes * (10 MB / minute)) = 1,200,000 MB (just over 1 TB). 320 Kilobits per second encoding == 2400 Kilobytes per minute == about 23%...