Backplane

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Backplane

A backplane (or "backplane system") is a circuit board (usually a printed circuit board

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using Conductor pathways, or signal traces, industrial etchinged from copper sheets laminated onto a non-conductive substrate....
) that connects several connectors

Electrical connector

An electrical connector is a Electrical conductor for joining electrical circuits together. The connection may be temporary, as for portable equipment, or may require a tool for assembly and removal, or may be a permanent electrical joint between two wires or devices....
in parallel to each other, so that each pin

A pin is a device used for fastening objects or material together.Pin may also refer to:* Award pin, a small piece of metal or plastic with a pin attached given as an award for some achievement...
of each connector is linked to the same relative pin of all the other connectors, forming a computer bus

Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
. It is used as a backbone to connect several printed circuit boards together to make up a complete computer system. Early personal computers like the Apple II and the IBM PC

IBM PC

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform ....
integrated an internal backplane for expansion card

Expansion card

An expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard to add additional functionality to a computer system....
s.

While a motherboard may include a backplane, the backplane is actually a separate entity.

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Encyclopedia

A backplane (or "backplane system") is a circuit board (usually a printed circuit board

Printed circuit board

Electrical connector

Computer bus

IBM PC

Expansion card

Motherboard

A motherboard is the central printed circuit board in some complex electronic systems, such as modern personal computers. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple Inc....
by the lack of on-board processing power where the CPU

Central processing unit

A central processing unit is an electronic circuit that can execute computer programs. This broad definition can easily be applied to many early computers that existed long before the term "CPU" ever came into widespread usage....
is on a plug-in card.

Backplanes are normally used in preference to cables because of their greater reliability

Reliability engineering

Reliability engineering is an engineering field, that deals with the study of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time....
. In a cabled system, the cables need to be flexed every time that a card is added to or removed from the system; and this flexing eventually causes mechanical failures. A backplane does not suffer from this problem, so its service life is limited only by the longevity of its connectors. For example, the DIN 41612

DIN 41612

DIN 41612 is a DIN standard for electrical connectors that are widely used in rack based electrical systems. Standardisation of the connectors is a pre-requisite for open systems, where users expect components from different suppliers to operate together....
connectors used in the VMEbus

VMEbus

VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of Central processing unit, but later widely used for many applications and standardized by the IEC as American National Standards Institute/Institute of Electrical and Electronics Engineers 1014-1987....
system can withstand 50 to 500 insertions and removals (called mating cycles), depending on their quality.

In addition, there are bus expansion cables which will extend a computer bus to an external backplane, usually located in an enclosure, to provide more or different slots than what the host computer provides. These cable sets have a transmitter board located in the computer, an expansion board in the remote backplane, and a cable between the two.

Active backplanes

Backplanes have grown in complexity from the simple ISA

Industry Standard Architecture

Industry Standard Architecture was a computer bus standard for IBM compatible computers....
(used in the original IBM PC

IBM PC

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform ....
) or S-100

S-100 bus

The S-100 bus, IEEE696-1983 , was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer ....
style where all the connectors were connected to a common bus. Because of limitations inherent in the PCI

Peripheral Component Interconnect

The PCI Local Bus , or Conventional PCI, is a computer bus for attaching computer hardware in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification or an expansion card that fits into a socket....
specification for driving slots, backplanes are now offered as passive and active.

Passive backplanes offer no active bus driving circuitry. Any desired arbitration logic is placed on the daughter cards. Active backplanes include chips which buffer

Buffer (computer science)

In computing, a buffer is a region of Memory used to temporarily hold data while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device or just before it is sent to an output device ....
the various signals to the slots.

The distinction between the two isn't always very clear, but may become an important issue if a whole system is expected to have no single point of failure

Single Point of Failure

A Single Point of Failure, , is a part of a system which, if it fails, will stop the entire system from working. They are undesirable in any system whose goal is high availability, be it a network, software application or other industrial system....
. A passive backplane, even if it is single, is not usually considered a SPOF. Active backplanes are more complicated and thus have a non-zero risk of malfunction.

Backplanes in storage

Backplanes have also become commonplace for connecting multiple hard drives to a single disk array controller

Disk array controller

A disk array controller is a device which manages the physical disk drives and presents them to the computer as Logical Unit Number. It almost always implements RAID#Hardware RAID RAID, thus it is sometimes referred to as RAID controller....
. Backplanes are commonly found in disk enclosure

Disk enclosure

A disk enclosure is essentially a specialized chassis designed to hold and power disk drives while providing a mechanism to allow them to communicate to one or more separate computers....
s, disk array

Disk array

A disk array is a disk storage system which contains multiple disk drives. It is differentiated from a disk enclosure, in that an array has cache memory and advanced functionality, like redundant array of independent disks and virtualization....
s, and server

Server (computing)

A server is a computer program that provides services to other computer programs , in the same or other computer. The physical computer that runs a server program is also often referred to as server....
s.

Backplanes for SAS and SATA HDDs most commonly use the SGPIO

SGPIO

SGPIO is an acronym for Serial General Purpose Input/Output which is a 4-signal bus used between a Host Bus Adapter and a backplane - of the 4 signals, 3 are driven by the HBA and 1 by the backplane....
protocol as means of communication between the HBA

Host adapter

In computer hardware, a host controller, host adapter, or host bus adapter connects a host system to other computer network and computer storage devices....
and the backplane. Alternatively SCSI Enclosure Services

SCSI Enclosure Services

Most recent SCSI disk enclosure products support a protocol called SCSI Enclosure Services . The SCSI initiator can communicate with the enclosure using a specialised set of SCSI commands to access power, cooling, and other non-data characteristics....
can be used. With Parallel SCSI

Parallel SCSI

Parallel SCSI is one of the interface implementations in the SCSI family. In addition to being a Bus , SPI is a Parallel communications electrical bus: There is one set of electrical connections stretching from one end of the SCSI bus to the other....
subsystems, SAF-TE

SAF-TE

In computer computer data storage, a SCSI Accessed fault-tolerant system Disk enclosure is an industry standard to interface an enclosure to a SCSI subystem to gain access to information or control concerning...
is used.

Midplane

Whereas cards and devices connect to only one side of a backplane, a midplane has cards and devices connected to both sides. This ability to plug cards into either side of a midplane is often useful in larger systems made up primarily of modules attached to the midplane. Midplanes are used in computers, mostly in blade server

Blade server

Blade servers are self-contained all-inclusive server with a design optimized to minimize physical space. Whereas a standard 19-inch rack server can exist with a power cord and network cable, blade servers have many components removed for space, power and other considerations while still having all the functional components to be consider...
s, where server blades reside on one side and the peripheral (power, networking, and other I/O) and service modules reside on the other. Midplanes are also popular in networking and telecommunications equipment where one side of the chassis accepts system processing cards and the other side of the chassis accepts network interface cards.

Platforms

PICMG

A Single Board Computer meeting the PICMG 1.3 specification and compatible with a PICMG 1.3 backplane is referred to as a System Host Board

System Host Board

System Host Board is a term applied to a Single Board Computer meeting the PICMG 1.3 specification. PICMG 1.3 extended the previous PICMG specifications to continue support for Peripheral Component Interconnect/PCI-X plug in cards as well as new support for PCI-Express....
.

In the Intel Single Board Computer world, PICMG

PICMG

The PCI Industrial Computer Manufacturers Group is a consortium of over 250 companies who collaboratively develop open specifications that adapt PCI technology for use in high-performance telecommunications and industrial computing applications....
provides standards for the backplane interface: PICMG 1.0, 1.1 and 1.2 provide for ISA and PCI support with 1.2 adding PCIX support. PICMG 1.3 provides for PCI-Express support.

Backplane

Active backplanes

Backplanes in storage

Midplane

Platforms

PICMG

See also