Arbitration in shared resource

The need for more powerful and faster systems gave birth tomulTIprocessing and mulTI-tasking systems. But to achieve this, costand reliability were not to be sacrificed. To reduce cost it is vital toshare resources, but to do so requires reliable means of arbitraTIon.In a mulTIprocessing system, a single bus may be shared betweenvarious processors or intelligent peripherals. The resources sharedby processors (Figure 1) are generally termed as global resourcesand those shared between the local processor and the peripherals(Figure 2) are typically known as local resources. Whether local orglobal, there always exists a protocol that will connect anddisconnect various devices to and from the shared resources.Various bus architectures in existence today have different ways ofdoing this.No matter what the protocol of a specific bus, there is always amethod which dictates how arbitration shall be performed betweentwo or more devices. Some systems employ synchronous arbitrationand some use an asynchronous approach. The third option is not touse arbitration at all, but instead to employ time-multiplexing. This isused mainly in data communications by dividing the common mediainto various time slots. Each processor (station) is assigned apredetermined time for using the media. If the station does not needto use the media during its assigned time-slot, it may pass control tothe next station. This obviously results in an inefficient use of thebus bandwidth.