Legacy pages are pages that are no longer considered current; they contain references to obsolete equipment, techniques, etc. However they do still have a value.
Over the years we've built up a lot of tutorials and reference material about things that have since become obsolete. However we've found a surprising number of people still needing help with these older systems so we're keeping our "obsolete" resources available indefinitely.
These legacy pages are also an interesting and useful archive for anyone wanting to know how things were done in times past.
Examples of legacy pages: