- on Education & Information
- Published in issue 4/2001 on page 0
PCI Bus Prototyping Card (2)
developments from ISA to PCI
Ever since IBM-compatible PCs have been available, a new bus system has been introduced each time there was a major development step. The PCI bus, which represents the current state of affairs, is not limited to IBM-compatible computers and should survive for several PC generations, thanks to its high level of performance. The price for this is a relatively complex structure, which is thoroughly described in this article.In 1985, IBM unveiled the first AT computer. The bus system used at that time was the ISA bus. Shortly after this introduction, however, it quickly became evident that the ISA bus no longer represented the current state of technical development. It was clear that ’286 processors were already being slowed down by the bus, for example when working with graphics cards or high-speed network technologies. This large loss in performance was due to backwards compatibility with older 8-bit systems. The rather low bus clock rate of 6 MHz, which was later increased to 8 MHz, also did not help matters. The result was a theoretical data transfer rate of 8 MB/s with a bus width of 16 bits. In actual practice, however, the maximum achievable data rate was around 4 to 6 MB/s.