ePCI-X, a PCI-Only Evolution for PCI/ISA Systems

Most new designs based on the popular PCI/ISA form factor have no requirements for the ISA bus. They demand more I/O bandwidth, especially in the form of the PCI-X extension to the PCI specification. Also, recent chipsets have no support for an ISA bus and can even be hostile to the addition of a PCI-to-ISA bridge. The ISA bus is now a cumbersome, expensive, and often useless feature that imposes restrictions on chipset choice.

Those were the motivations of the PICMG 1.2 subcommittee that developed the Embedded PCI-X, or ePCI-X specification. This PCI-only specification was approved in January 2002 by PICMG executives. It defines a single board computer and backplane system with one or two PCI or PCI-X busses.

Two board sizes are defined. A half-size single-bus board, similar to half-size ISA SBCs, targets applications where space is a concern. The full-size single or dual-bus board is intended for more I/O intensive applications. Hence a very broad range of applications are covered, from the plain vanilla 32-bit 33MHz PCI single-bus computers, or up to 16x more I/O bandwidth with the full-fledge dual PCI-X busses at 133MHz.

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