Before having distributed systems there existed multiuser systems built around
a single time shared computer. UNIX is one of the best-known operating systems
for multiuser systems.
Since UNIX was already in widespread use and easily available, a lot of
distributed system researchers extended UNIX as a basis for distributed
systems. The first extension, developed at the University of California at
Berkeley (BSD) in the late 1970s, was interprocess communication.
The distributed UNIX model outlined in figure 2 above is the result of
the extension contributed by Sun Microsystems: the remote procedure call
(RPC) that led to the development of the network file system (NFS) and
network information system (NIS).
Although the development of distributed UNIX systems offers obvious commercial
and technical advantages, UNIX was originally designed to meet a restricted
range of requirements in a time when the limitations of computer hardware
restricted the scope of the designers' ambitions. In the recent past a new
generation of distributed operating systems has been developed. Mach, Chorus
and Amoeba are operating systems which have been developed as true distributed
systems.
