Modern day public libraries in Britain are linked on a nation wide computer network. A library in Cardiff, Wales can discover that a rare special book a customer wants is available in Sheffield, England, and can order it. Go to your local library and the librarian can, on using your library number from your plastic card, see all the books you have taken out, and those books you have still to return. Unlike the old card system that was isolated to that one library, any changes to the computer is instantly updated on the whole system.