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PCIe 4.0 Specs Revealed: 16GTps Rate and Not Just For Graphics Cards Anymore (tomshardware.com)
Freshly Exhumed writes: PCI-SIG has released the specifications for version 4.0 of the PCIe (Peripheral Component Interconnect Express) bus, which, according to Chairman Al Yanes, promises data transfer rates of 16GTps, extended tags and credits for service devices, reduced system latency, lane margining, superior RAS capabilities, scalability for added lanes and bandwidth, improved I/O virtualization and platform integration. Tom's Hardware has posted a slide deck of the new version's specifications.
Giga Transfers, double version 3
Wow, sent an e-mail as suggested when clicking on "use classic" banner, and got a fast response that addressed my msg
GigaTransfers per second, essentially the clock speed of the bus. The bandwidth can then be found by multiplying the number of transfers per second with the bus width, and adjust for the encoding overhead (8/10 for PCIe 2.0 and earlier, 128/130 for PCIe 3.0 and above).
So, 4x (lane) PCIe 4.0 can do 16 * 4 * 128 / 130 = ~63Gb/s or ~7.9GB/s.
Wikipedia got a nice table: https://en.wikipedia.org/wiki/PCI_Express#History_and_revisions.
After actually reading the NVMe spec, it's specifically designed to be used over PCI Express. Other transports look to be an afterthought. NVMe over Fabrics is a separate specification for using NVMe over non-PCI* interfaces.
NVMe 1.2 was only intended to be used over PCI type interfaces, primarily PCI Express, but also PCI and PCI-X.