Although watching TV shows from the 1970s suggests otherwise,
the era wasn't completely devoid of all things resembling modern
communication systems. Sure, the 50Kbps modems that the ARPANET
ran on were the size of refrigerators, and the widely used Bell
103 modems only transferred 300 bits per second. But long
distance digital communication was common enough, relative to
the number of computers deployed. Terminals could also be hooked
up to mainframe and minicomputers over relatively short
distances with simple serial lines or with more complex
multidrop systems. This was all well known; what was new in the
'70s was the local area network (LAN). But how to connect all
these machines? The point of a LAN is to connect many more than
just two systems, so a simple cable back and forth doesn't get
the job done. Connecting several thousands of computers to a LAN
can in theory be done using a star, a ring, or a bus topology. A
star is obvious enough: every computer is connected to some
central point. A bus consists