Page "Bus (computing)" Paragraph 7

In modern systems the performance difference between the CPU and main memory has grown so great that increasing amounts of high-speed memory is built directly into the CPU, known as a cache.

In such systems, CPUs communicate using high-performance buses that operate at speeds much greater than memory, and communicate with memory using protocols similar to those used solely for peripherals in the past.

These system buses are also used to communicate with most ( or all ) other peripherals, through adaptors, which in turn talk to other peripherals and controllers.

Such systems are architecturally more similar to multicomputers, communicating over a bus rather than a network.

In these cases, expansion buses are entirely separate and no longer share any architecture with their host CPU ( and may in fact support many different CPUs, as is the case with PCI ).

What would have formerly been a system bus is now often known as a front-side bus.