Computer Senility is a concept that considers how a sentient computer might develop mental instability if left alone for millions of years.
Computer senility would therefore be a product of lasting loneliness. The sentient computer in question is Holly. Initially having an intelligence quotient (IQ) of 6,000, Holly becomes very strange after Red Dwarf has drifted through deep space for three million years. One of Holly's odd activities alone included Hol Rock, a form of decimalized music with two extra notes that Holly invented, "H" and "J".(RD: Kryten) He also has a collection of singing potatoes to keep himself sane. (RD: Queeg)
Holly also came up with an idea of serving a two year prison sentence in just fourteen weeks. Unfortunately for Lister, he'd have to become a dog. (RD: Cassandra) His current IQ is only 68. Holly brings Dave Lister out of stasis partly because s/he (Holly underwent a "head sex change" later in the series) is so lonely, and partly because the radiation from Red Dwarf's engine failure had dropped to a safe background level. (RD: The End)
Holly briefly regained more than twice her original IQ in a scheme devised by Kryten and tested on Talkie Toaster. Kryten also claimed that he knew a fellow mechanoid who was senile, whose name was Gilbert but preferred being called "Rameses Niblick the Third Kerplunk Kerplunk Whoops Where's My Thribble". (RD: White Hole)
The "droid rot" suffered by Kryten's Spare Head Three is presumably a related condition. This seemed to manifest itself in outraged rants against Kryten, made in a Yorkshire accent. (RD: D.N.A.) A vending machine on Red Dwarf also seemed to suffer from computer senility. It spoke with a lisp and got black coffee mixed up with a bucket. (RD: Future Echoes)