System bus

The technique was developed to reduce costs and improve modularity, and although popular in the 1970s and 1980s, more modern computers use a variety of separate buses adapted to more specific needs.

In what became known as the Von Neumann architecture, a central control unit and arithmetic logic unit (ALU, which he called the central arithmetic part) were combined with computer memory and input and output functions to form a stored program computer.

Engineers used the common techniques of standardized bundles of wires and extended the concept as backplanes were used to hold printed circuit boards in these early machines.

[7] Modularity and cost became important as computers became small enough to fit in a single cabinet (and customers expected similar price reductions).

The passive backplanes of early models were replaced with the standard of putting the CPU and RAM on a motherboard, with only optional daughterboards or expansion cards in system bus slots.

[13] The easiest way to implement symmetric multiprocessing was to plug in more than one CPU into the shared system bus, which was used through the 1980s.

[14] Even in very simple systems, at various times the data bus is driven by the program memory, by RAM, and by I/O devices.

To reduce the coherency traffic, a snoop filter was included in the higher-end chipsets, in order to have cache state information available on-chipset.

In 2007 Intel extended the idea of multiple buses in the 7300 chipset with four independent FSBs, calling it dedicated high-speed interconnects (DHSI).