Here at Trenton, we get a lot of questions about the PICMG 1.3 System Host Board specification. We’ve answered a few below, but the full spec can be found at www.picmg.org. Enjoy!
Q: Why call the PICMG 1.3 specification SHB Express and not SBC Express?
A: SHB means System Host Board and the technical subcommittee that wrote the specification felt that SHB provided a good way to avoid confusion with PICMG 1.0 and PICMG 1.2 SBCs that support the PCI/ISA or PCI-X/PCI parallel bus interfaces. A PICMG 1.3 system host board performs the same function as an SBC, but an SHB by virtue of the multiple PCI Express serial links along the board’s edge connectors supports multiple communication pathways into the SHB unlike the common parallel bus used in PICMG 1.0 single board computers.
PICMG 1.3 SHBs therefore can handle greater data traffic into and out of the board as compared to PICMG 1.0 SBCs. We use the term SHB Express to define a system host board that uses PCI Express as the primary interface to the backplane. The terms “SHB Express” and “PICMG 1.3″ are used interchangeably. Additionally, PICMG 1.3 SHBs must always be used with PICMG 1.3 backplanes.
Trenton's JXT6966 Single Board Computer
Q: What is meant by the terms “Server-Class” and “Graphics-class” as it relates to PICMG 1.3 board hardware?
A: Server and Graphics class refers to how the PCI Express electrical links are routed to the SHB’s card edge connectors A and B and how these links are in turn routed or “plumbed” to the option card slots and/or devices on a PICMG 1.3 backplane. Server-class SHBs usually feature two x8 PCI Express electrical links on edge connectors A and B plus either one x4 or four x1 PCIe links.
Graphics-class SHBs usually feature one x16 PCI Express electrical link on edge connectors A and B plus either one x4 or four x1 PCIe links. The type of chipset utilized in an SHB design determines if the board is a server- or graphics-class SHB. Matching the class of a PICMG 1.3 SHB to the PICMG 1.3 backplane class results in the maximum use of all available option card slots and devices on a PICMG 1.3 backplane.
Q: Does the PICMG 1.3 specification provide support for PCI Express Gen 2 products and can a PCI Express serial communication link support multiple PCI Express card slots like a PCI or PCI-X parallel bus?
A: Provisions have been worked into the specification that allow the PICMG 1.3 SHBs and backplanes to support both PCI Express Gen 1 and Gen 2 hardware. Remember that PCI Express is a point-to-point, high speed and scalable bandwidth serial communication interface and as such cannot support multiple card slot interfaces without some help. While the chipsets support multiple PCI Express links that can be routed to a PICMG 1.3 backplane to support a number of PCI Express option card slots, PCI Express fan-out switches or simply PCIe switches are also commonplace in many backplane designs.
A PCI Express fan out switch takes an incoming PCI Express link and produces multiple PCI Express links. The basic function of a PCIe switch is similar to that of a PCI-to-PCI bridge chip in that the PCIe switch enables support for multiple PCI Express option card backplane slots.
PICMG 1.3 system host boards and backplanes are widely deployed in a wide range of mission critical applications, including Government & Defense, Virtualization, GPU Computing and Video Processing. Trenton integrates these PICMG 1.3 boards in a number of fully integrated systems, such as the new TCS4500 4U rackmount computer which features the JXT6966 Single Board Computer and Trenton’s BPC7041 PCI Express 2.0 Backplane.
Trenton's TCS4500 Rackmount Computer
