Your OS depends on the keyboard. HP 400s were the "hybrid" models made after HP acquired Apollo, so from the factory they were set up to run either HP-UX (9 or earlier) with a HP-HIL keyboard or mouse, or DOMAIN/os (Aegis) with a Domain keyboard. Switching between the two requires keyboard/mouse swap and setting one value in the NVRAM. I've only used DOMAIN on my 425, since HP-UX of the early '90s has been described as not spectacular. SR10.4 works well, and with the y1k997 patches it seems to tick along just fine in the 21st century. DOMAIN is neat since it's so network-transparent and very unusual, but with the BSD or SysV environments the learning curve is not nearly as big as with the Aegis environment. Of course, NetBSD can be run on them with a HP-HIL keyboard setup as well, but I think it's pretty evident which camp I'm in. Bear has some manuals on his site (www.typewritten.org) Scott