Main Boards and Backplanes
ImageStream can supply main boards and backplanes for a wide range of integrated product applications. In general, backplanes are more reliable and easier to service than a main board. If a main board fails, the entire system must be disassembled to replace it. If a single board computer fails in a passive backplane system, the SBC is simply replaced like any other card.
The main drawbacks of using a backplane and SBC are cost and size. You can expect systems that use passive backplanes and SBCs to cost more than an integrated main board. With regard to size, some SBCs are full length cards that require a full length backplane. There are also several half-length backplane and SBC configurations available for deploying half-length interface cards in very small enclosures. Half-length backplane systems are generally more expensive than larger format systems, and they are also more expensive than comparable embedded main boards. As a result, embedded main boards are commonly used in applications that require diminutive chassis.
Main Boards
Some chassis are designed to accept main boards, some are designed to accept either a main board or a backplane, and some are designed to accept only a backplane. For example, ImageStream's Rebel chassis uses an embedded main board, while the R1 and Enterprise are only available with a passive backplane, and the Gateway chassis offers options for both.
One of the best reasons to use a main board is cost. Most embedded main boards can be used in standard PC applications, which means that they often benefit from larger economies of scale. Main boards do not have an expansion bus connector between the processing unit to the data bus. This reduces part counts and cost, and enables the design of embedded main boards that fit in more compact enclosures.
Backplanes
There are essentially two different backplane standards that ImageStream supports: the PICMG industrial computer standard for PCI backplane applications, and the CompactPCI backplane standard for more demanding carrier-class applications. As subsets of these standards, a wide range of complementary buses and switch fabrics are also available.
Depending on your needs, there are several PCI standards that can be deployed. For example, the lowest cost PCI backplanes are 32-bit, 33 MHz backplanes that provide a maximum of 1 Gbps throughput. The most expensive PCI backplanes support 64-bit PCI cards. Some of these 64-bit backplanes provides PCI slots that operate at 33 MHz for 2 Gbps maximum throughput, 66 MHz for 4 Gpbs maximum throughput, or 133 MHz for 8 Gbps maximum throughput.
PCI Signaling Voltage
When industry engineers decided to expand PCI bus standards to support 66 MHz clock speeds, they found that the current required to drive the faster bus would render most standard power supplies inadequate. As a result, the standards engineers decided to develop a lower voltage PCI signaling standard that would drop the voltage from 5 volts down to 3.3 volts. 3.3 volt PCI signaling is not compatible with components that use 5 volt signaling and vice versa. As a result, a keying system was developed to prevent cards from being inserted into an incompatible slot.
To ease signaling compatibility issues, many manufacturers have developed PCI cards that provide "universal signaling." This means that the card will support both 3.3 volt and 5 volt signaling. Many of these universal signaling cards can also detect the speed of the PCI bus automatically, which makes it possible for these cards to work with just about any PCI bus configuration.
Other PCI cards will only support one of the two signaling standards. For example, you may have a 64-bit 66 MHz PCI card that does not support universal signaling, and it does not provide automatic bus speed detection. This type of card can only be installed in a 64-bit 66 MHz slot that is keyed for the appropriate voltage (probably 3.3 volts).
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CompactPCI
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