Bus

Transportation

For most people the bus is a way of transport. A bus is a large vehicle designed to carry as many people as possible in reasonable comfort, and sometimes unreasonable discomfort over short and long distances. Many people rather drive their own car than use the bus. This is understandable if you live in the USA. However, every time you drive your own car instead of the bus you kill a kitten or some piece of nature. Naturally you do the same when you use the bus, except that the guilt is spread over many people.

Computers

In computers bus denotes a set of bits. there are 2 primary buses in computers. data bus and address bus. intels 8080 had an 16 bit address bus and a 8 bit data bus. the data bus was multiplexed onto the lower 8 bits of the address bus. motorolas 6809 had 2 seperate buses. the address bus is used to access memory. in the above examples the address bus could access 65536 (64K) of memory. the data bus held the data that is to be stored, or retrieved, at the address on the address bus

there is a third bus called the I/O bus. this bus has several differebnt lines depending on whether the bits are transmitted serialy or in parallel.

the motorola CPUs had what is called memory mapped I/O. data from peripherals was treated like a memory location, therefor it could be accessed direcly by assembly language.