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Frequently asked questions
PCI Express PCI-SIG, PCI, and PCI Express (PCIe) FAQ
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What is the PCI-SIG? |
| A |
Formed in 1992, the PCI Special Interest Group (PCI-SIG) is the industry organization chartered to develop and manage the PCI standard.
Their website is www.pcisig.com.
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| Q |
How does PCI Express differ from PCI? |
| A |
PCI Express is a new standard that overcomes the speed limitations of PCI, pushing the data rate to 2.5Gbps and beyond.
The bus architecture of PCI has restricted its data rate because the skew between the clock and data lines becomes excessive as the rates increase.
PCI Express (also written as PCIe) replaces PCI's bus architecture with a serial I/O structure that uses a clock, embedded in the data, to solve the skew problem.
In addition to providing faster data transfer rates, PCI Express simplifies PCB design and lowers overall cost because it uses only four signal pins, compared to the 49 used with PCI.
PCI Express also comprehends different data types, provides extended configuration attributes, offers power management and quality of service features, supports hot plug and hot swap, and provides superior data integrity and error handling.
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| Q |
How does v1.1 of the PCI Express specification differ from v1.0a? |
| A |
Most of the changes from v1.0a to v1.1 relate to the protocol layers.
As far as the physical layer is concerned, version 1.1 modifies the physical layer by relaxing the transmitter differential return loss budget from 12dB to 10dB and the receiver differential return loss budget from 15dB to 10dB.
In addition, Version 1.1 performs Tx and Rx eye measurements with a "clean" clock, reduces the Tx eye budget from 0.70UI to 0.75UI, and restricts PLL bandwidth.
For more details, please visit the PCI SIG website at www.pcisig.com.
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| Q |
Is PCI Express software compatible with PCI? |
| A |
Yes.
To ensure that all existing applications and drivers operate unchanged, the PCI Express protocol maintains the PCI addressing model (a load-store architecture with a flat address space).
As long as there are no new PCI Express features needed, the system will operate as usual.
PCI Express software can boot in existing operating systems without any OS or BIOS changes and no changes are required for the configuration and software driver models.
Software for power management is also compatible.
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Other Questions
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