Part of the Internet Archive, which also covers archived moving images (The Internet Moving Images Archive), audio and software, the Wayback Machine holds cached versions of thousands of websites and billions of pages, allowing users to look at sites that are no longer available or at earlier versions of ones that are still around. An invaluable resource that, due to the gigantic nature of the holdings, is slightly hampered by the fact that no list of the holdings can be easily provided. This means inevitably that correct recall of the URL in question is necessary, or failing that, searching for it on the web first.