Described most simply, the internal computer bus serves to transfer data between the computer’s CPU and its peripheral components, such as its hard-drive, memory, sound and video systems. Consequently, usable PC performance is limited by bus capacity. Unfortunately, bus capacity has during various eras of PC development lagged behind advancements in the performance of CPUs and peripherals.
Advantech’s white paper, Industrial Bus and Network Standards, provides a detailed history of the transitions of bus standards from the Industry Standard Architecture (ISA), limited to 16 bit at 4.77 MHz, and Extended Industry Standard Architecture (EISA), with capacity of 32 bits at 8 Mhz, to Apple’s NuBus and SCSI, which formats delivered the known benefits of standardization, but at the cost of intrinsic limitations that were too quickly overrun by CPU advances, particularly with respect to the increasing demands of industrial and video-intensive applications. Their lack of plug-and-play (PnP) readiness also served to hasten their inevitable demise. Although the next-generation standard was proposed in 1991, these older formats continued to dominate until the introduction of Windows 95 and its support for PnP.
Industry-wide adoption of the PCI (Peripheral Component Interconnect) standard in 1993 brought bus performance back to within the ranges of rapidly improving CPU and peripheral performance. PCI also offers the advantage of being basically transparent – components connected to the CPU via PCI bus architecture appear to the processor as if connected directly to it. While the PCI standard has since been eclipsed by PCIe (PCI Express), modern PCs typically feature two or more buses, one of which is still of the PCI standard.
With a capacity ranging from 133 to 533 MB/s, the PCI standard served well until CPU speeds increased well beyond that (to greater than 3 GHz), necessitating a new PCI-standard, PCIe. PCIe extends that range to from 250 to 1969 MB/s per lane, but, as noted, not all peripherals require that extreme capacity – many modern disk drives and sound cards still communicate effectively via PCI. But as Advantech notes, PCIe can perform at up to 30 times the capacity of PCI and is scalable, supporting such innovations as virtualization of physical I/O. So, as the demands of video applications have increased, PCIe has become the standard interface for gaphics cards. Apple has recently championed a variation of PCIe known as Thunderbolt that is specifically designed to enhance graphic-display and human-machine interface performance as video and game play become more mainstream uses for PCs.
But despite subsequent advancements offered by the ever-improving versions of PCIe, the game-changing PCI standard remains a key ingredient of modern PC designs.
Tell me what your networking and peripheral needs are and I can work with you to create a customized industrial computing solution. You can email me at jeremy.miller@L-Tron.com or call me at 1-800-830-9523 x126.