the data bus. More complex systems have a multi-master bus—not only do they have many devices that each drive the data bus, but also have many bus masters that each drive the address bus. The address bus as well as the data bus in bus snooping systems is required to be a bidirectional bus, often implemented as a three-state bus. To prevent bus contention on the address bus, a bus arbiter selects which particular bus master is allowed to drive the address bus during this bus cycle. Dual Independent Bus Intel has used the term Dual Independent Bus (DIB) for two different purposes. The first one came when Intel changed from a single local bus to the DIB, using the external front-side bus to the main system memory and I/O devices, and the internal back-side bus to the L2 CPU cache. This was introduced in the Pentium Pro in 1995. In 2005 and 2006 Intel introduced the 8500 and 5000 chipsets, where DIB referred to the two front-side buses on a chipset, which doubles the system bandwidth compared to having just one FSB shared by all the CPUs. However, the information needed to guarantee the cache coherence of shared data located in different caches have to be sent in broadcast (snooped) to check the other FSB's CPUs' cache state, reducing the available bandwidth. 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). The system bus approach is obsolete in the modern personal and server computers, which instead use higher-performance interconnection technologies such as HyperTransport and Intel QuickPath Interconnect, while the system bus architecture continued to be used on simpler embedded microprocessors. The systems bus can even be internal to a single integrated circuit, producing a system-on-a-chip. Examples include AMBA, CoreConnect, and Wishbone. See also Bus (computing) External Bus Interface Expansion bus References Computer buses