Bus Evolution

The importance of bus evolution is visible in terms of the clocking signal increases , numbers of data lines, interrupt sharing, and something called bus mastering. Bus mastering allowed additional processors and devices (for example, IDE and SCSI adapters) to contend for bus processing. By contrast, previous architectures where the system processor had complete control of the bus and scalability became problematic .

The decoupling of the bus through bus mastering from a single point of control came with IBMs Micro Channel Architecture (MCA); however, it was enhanced with EISA to include auto and software configuration functions. This first laid the groundwork for plug ˜n play functionality, while the second aided in reconfiguring the bus (changing device priorities, addressing, and so on).

Note 

This standard bus architecture (Extended Industry Standard Architecture or EISA) extends the ISA standard from a 16-bit to a 32-bit interface.

The physical decoupling and enhanced scalability of the bus was achieved with the Peripheral Component Interconnect Standard (PCI) and the resulting PCI mezzanine bus architecture. This was the first bus implementation not tightly coupled with the system processor. This allowed the PCI bus to expand its connectivity by using a re-configurable structure and bridging, as necessary, to add additional hardware devices.