Online music services might make it seem like every track that’s ever been recorded is now available for purchase and digital download—with each service claiming to offer millions of music tracks—but the simple fact is that vast collections of music are not available online in any form. Sometimes these are limited-release recordings on obscure labels, where master recordings may not be available, and many others are archival or historic recordings that may never make it online. But there are a few holdouts among popular performers, too: Metallica took a long time to come around to digital sales, and (of course) The Beatles catalog has yet to come online.
