The CompactFlash Association (CFA) has announced the release of the next-generation CFexpress 4.0 memory card standard. The update builds on the original CFexpress 2.0 standard developed in 2016 which is now commonplace in the digital camera sector. Version 4.0 promises to double the maximum theoretical transfer speed of a Type B card from the current 2000MB/s to 4000MB/s, all while maintaining full backward compatibility with existing CFexpress cameras and devices. If you're wondering what happened to the CFexpress 3.0 standard, well, confusingly it seems to have been skipped altogether. The seemingly non-existent CFexpress 1.0 standard did in fact exist, but was badged as XQD.
The secret to version 4.0's speed increase is the use of the PCI Express Gen4 interface, which allows for twice the transfer speed of the Gen3 interface used by current (version 2.0) CFexpress cards. Interestingly the Gen4 interface isn't exactly new - it was formally announced in 2017, with retail PC components like motherboards and graphics cards adopting the standard in 2019. As with Gen3, the final speed of PCIe Gen4 depends on how many data transfer 'lanes' have been implemented for a particular hardware application. Though both generational standards can transfer over a maximum of 16 lanes, CFexpress Type B cards only use two PCIe lanes, and Type A cards just one. However, with PCIe Gen4 doubling the speed each lane is capable of, CFexpress 4.0 Type B cards will now have a maximum transfer rate of 4000MB/s, and Type A cards up to 2000MB/s.
It's unlikely we'll see CFexpress 4.0 cards perform quite at these speeds though. While the current CFexpress 2.0 Type B cards theoretically top out at 2000MB/s, the fastest cards currently available boast max reads speeds of up to 1900MB/s. Likewise, the fastest existing Type A cards are rated for 900MB/s - 100MB/s short of the current 1000MB/s theoretical PCIe Gen3 1-lane speed limit.
The news that much faster CFexpress cards are in the pipeline is exciting, but we'll probably have to wait a while to see retail examples of CFexpress 4.0 cards. There is often a time delay of at least a year between the announcement of a new technological standard and retail availably of compatible products. We'd also wager that there'd be limited demand for even faster (and presumably much more expensive) CFexpress Type B cards, as the best CFexpress cards are already more than fast enough to record 8K footage and capture burst sequences of very high resolution raw stills.