PCI-104 Form Factor

Following along a previous posting about the slow adoption of new interface bus standards, I have yet another one. Upgrading the page that covers PC104 board manufacturers and separating out vendors that produce only PCI104 cards, I don't find that many companies producing PCI/104 boards.

The attached graphic shows the road-map [up-grade path]. The PC104 standard started out with an IBM XT bus interface in a 90mm x 96mm board format in 1992. Following that release, the IBM AT bus interface was added a few years later. Then in 1997 the PCI bus interface was added to reside along side the PCAT bus, as a new connector. With each upgrade board area was reduced because of the increase in the number of connectors. However; card-to-card transmission speed increased as the interface buses increased their throughput.

The PCI104 specification was released in 2003. The change here was to leave the PCI interface, now common, and remove the connectors and interfaces dedicated to the out-dated PCAT bus which than freed up board space.

Odd that there are still not that many PCI/104 board vendors. The stack height is reduced form 6 cards to 4 cards, but they may still be stacked using the PCI104 standard. Could it be that the CPU card is the only CCA that requires a PCI interface, while all the other I/O cards don't benefit from being redesigned? Maybe the increased density of FPGAs compensated for the reduced board area? Perhaps most OEMs require a 6-card stack in a PC/104 chassis. What ever the reason, the original PC bus lives on......

Graphic; The different connector locations for each PC/104 board format.