Dual Pentium PCI-ISA Passive Backplane Single Board Computer
PCI-ISA and PCI Express Passive Backplane Standard
Introduction
The PCI-ISA Passive Backplane Standard was developed by PICMG member companies to adapt desktop PCI/ISA standards and later the PCI Express standard for industrial applications.
Dual Pentium PCI-ISA Passive Backplane Single Board Computer
Desktop
computers generally have most of their circuitry on a single large "motherboard"
that mounts to the bottom of the computer's chassis. While this is the least
expensive packaging method, it leaves a lot to be desired when used in
industrial applications. The motherboard, usually constructed from 0.062"
material, is thin enough and large enough to flex when inserting plug-in boards.
This flexure can, and often does, break small traces and solder joints on fine
pitch surface mount devices. Replacing a motherboard necessitates complete
disassembly, removing all cards and cables from the system. Downtime ranges from
30 minutes to several hours. This is unacceptable for many critical industrial
or telephony applications. Since motherboard technology changes literally
monthly, it is usually impossible to find an exact replacement. Using another
motherboard often causes software problems due to BIOS changes, changing device
drivers, and different timing. These can take days or weeks to completely solve.
The
PCI-ISA passive backplane standard moves all of the components normally located
on the motherboard to a single plug-in card. Looking much like a standard ISA or
PCI card, a PCI-ISA CPU card has two edge connectors on it - one for the PCI bus
and one for the ISA bus. The "motherboard" is replaced with a simple
"passive backplane" that has only connectors soldered to it. This
backplane is simple and robust, with a very low likelihood of failure.
Passive
backplane systems have several advantages. First, they are more maintainable
than a motherboard system and have a much lower mean time to repair (MTTR).
Second, it is easy to upgrade to a newer and faster processor if desired. Third,
passive backplane CPU's are generally manufactured by industrial suppliers who
provide configuration control and longer product lifetimes than those typical of
the desktop world.
The basic specification in this series (denoted as PICMG 1.0) defines a CPU form factor and backplane connectors for PCI/ISA local bus specification.
The next specification (denoted as PICMG 1.1) defines the PCI-PCI Bridge Board Connector for Single Board Computer, including form factor and backplane connector layout.
The next specification (denoted as PICMG 1.2) standardizes the mechanical and electrical interface to support a standard form factor PCI computer system with either two PCI/PCI-X busses or a single PCI/PCI-X bus. This embedded PCI-X Specification (ePCI-X) is an evolutionary modification of the PICMG 1.0 PCI-ISA Specification; PCI-X capabilities are added to the PCI bus and the ISA bus is replaced by a second PCI-X bus. The board retains the same mechanical dimensions as PCI-ISA but the components move to the PCI side and the slot occupies a PCI position on a backplane.
The next specification, SHB Express, (denoted as PICMG 1.3) enhances the popular PICMG 1.0 (PCI) and 1.2 (PCI-X) specifications that defined passive backplane implementations of the desktop PC architectures. PICMG 1.3 continues that practice by mapping PCI Express onto a System Host Board (SHB) and an SHB Express backplane to accommodate the System Host Board and standard add-in cards. The specification defines the mechanical, signal mapping and power distribution requirements for System Host Boards and backplanes. In addition to providing support for new PCI Express add in cards, an SHB Express system will also support legacy PCI and PCI-X add in cards. The specification defines systems that can range from two slots for deeply embedded applications to up to 20 slots for complex, high performance solutions.
A more detailed description of the PCI-ISA Passive Backplane specification is available here.
The complete specifications can be obtained from PICMG Europe by using our order form.