What are the really unusual or weird computers?

Single Level Store: - The operating system and all user processes share a single large address space. - There is no filesystem: every database table, user profile, etc. is addressed by a pointer in this very large address space. This seems insane, but it works. There are a few things that make it work better: - database tables, user profiles, etc. are all well defined data structures. They are referred to 'objects', although I don't really think it is object oriented. - There is a lot of pointer checking going on to prevent overruns and accessing data that isn't yours. - Pointers are 'tagged' by the operating system to indicate if they are legitimate (ie: blessed by the OS and secure). If a user somehow manages to change a pointer in a non-blessed way, the 'tag' is lost. The old 48 bit CISC architecture (IMPI) was quite a weirdy compared to modern architectures.