PCI Express 4.0 (PCIe 4.0) doubles PCIe 3.0’s signaling rate to 16.0 gigatransfers per second (GT/s) per lane. The often-quoted 64 GB/s figure is the rounded, combined bandwidth of an x16 link in both directions—not the speed of data moving one way. After encoding overhead, PCI-SIG lists about 31.5 GB/s in each direction.
What PCIe 4.0’s 64 GB/s figure means
PCIe is a general-purpose input/output (I/O) standard used to connect components and peripherals. Its bandwidth figures depend on the number of lanes, the direction of traffic, and whether the number refers to raw signaling or usable bandwidth after encoding overhead.
PCI-SIG’s 2024 webinar comparison table lists 16.0 GT/s per lane and 252 gigabits per second (Gb/s) per direction for an x16 link after encoding overhead. Dividing 252 Gb/s by eight gives 31.5 gigabytes per second (GB/s) each way. Add the two directions and the total is 63 GB/s, commonly rounded to 64 GB/s. That aggregate figure does not mean an x16 connection sends 64 GB/s in one direction. PCI-SIG’s comparison table.
- 16.0 GT/s per lane: the signaling rate, doubled from PCIe 3.0.
- About 31.5 GB/s each way for x16: PCI-SIG’s listed bandwidth after encoding overhead.
- About 64 GB/s combined: the rounded sum of bandwidth in both directions.
When PCIe 4.0 specifications were released
Revision 0.9: feature complete in June 2017
On June 7, 2017, PCI-SIG announced publication of PCI Express 4.0 Revision 0.9. The organization described it as feature complete and said it was going through final intellectual-property review. This was a pre-final milestone, not the final Version 1.0 release. The announcement highlighted 16 GT/s data rates and flexible lane-width configurations. PCI-SIG’s Revision 0.9 announcement.
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Version 1.0: final specification
PCI-SIG later announced that PCIe 4.0 Specification Version 1.0 had been released and was available for download. It covers the architecture, interconnect attributes, fabric management, and programming interface used to design compliant systems and peripherals. The release notice does not establish a precise publication date, so the final release should not be assigned one based on the June 2017 Revision 0.9 announcement. PCI-SIG’s Version 1.0 release notice.
Compatibility with other PCIe generations
PCI-SIG says PCIe 4.0 maintains compatibility with earlier generations in software and mechanical interfaces. Its FAQ says an older card can be installed in a PCIe 4.0-capable slot, and a newer card can be installed in an older-generation slot. The link operates at the highest rate supported by the connected devices and configuration. PCI-SIG’s FAQ.
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That standards-level compatibility does not guarantee a specific device will fit a particular system, work with its firmware, receive a given number of lanes, or achieve a particular performance level. Check the system and component documentation for those details. A PCIe 4.0 NVMe SSD, for example, is a type of PCIe peripheral; its actual compatibility and performance depend on the drive and host platform specifications. Microchip’s PCI Express overview.
Where PCIe 4.0 is used
PCI-SIG lists servers, workstations, desktop and notebook PCs, tablets, embedded systems, peripheral devices, and high-performance computing among PCIe 4.0’s target applications. The standard aims to scale I/O bandwidth while considering cost, power, manufacturing, and compatibility. PCI-SIG’s PCI Express overview.
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PCI-SIG’s FAQ also says its feasibility analysis found 16.0 GT/s signaling over copper technically feasible at approximately PCIe 3.0 power levels. This is the organization’s feasibility finding, not a measured power result that applies to every product or configuration. PCI-SIG’s FAQ.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare PCIe bandwidth claims
When comparing generations or hardware specifications, check what each number describes rather than comparing GT/s directly with byte-per-second throughput. Use these distinctions:
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- Signaling rate: GT/s per lane.
- Lane width: the connection’s number of lanes, such as x16.
- Usable bandwidth: throughput after encoding overhead.
- Direction: bandwidth in one direction or the combined total in both directions.
- Platform support: the capabilities of the specific devices and system configuration.
PCI-SIG’s overview describes PCIe 4.0 as a general-purpose I/O standard, while its FAQ explains the generation’s signaling and compatibility. PCI-SIG’s overview and PCI-SIG’s FAQ.
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