And then, Sony needs to validate them to ensure that they will work properly. The PS5 will have an NVMe slot, but drive compatibility will be paramount. It's not just a bandwidth issue either, though clearly that is a factor. PS5's spec delivers six priority levels to developers, while the NVMe spec has just two.
"We can hook up a drive with only two priority levels, definitely, but our custom I/O unit has to arbitrate the extra priorities - rather than the M.2 drive's flash controller - and so the M.2 drive needs a little extra speed to take care of issues arising from the different approach," says Cerny. "That commercial drive also needs to physically fit inside the bay we created in PS5 for M.2 drives. Unlike internal hard drives, there's unfortunately no standard for the height of an M.2 drive, and some M.2 drives have giant heat sinks - in fact, some of them even have their own fans."
While the internal SSD solution is proprietary, with what might be considered a non-standard capacity, this will have no impact on the storage available from compatible M.2 drives, if you buy a 1TB or 2TB drive, that's the storage you'll have available. "The M.2 drive will have its own flash controller with its own (invisible) internal interface to its NAND flash dies. We don't know, or need to know, the details of that internal interface, or the size and type of NAND flash attached via that interface," Cerny explains. "What's relevant is the M.2 drive's external interface (eg four lanes of Gen4 PCIe so it can hook up to our flash controller) and the read bandwidth it can support via that interface."
In short, expandable storage is possible and you won't need proprietary drives from Sony to get the extra space you want. However, in the short term at least, the advice is simple: don't buy an NVMe drive without Sony validation if you plan to use it in PlayStation 5. Also remember that extreme bandwidth PCIe 4.0 NVMe drives are likely to be very expensive - in the short term, at least. This is cutting-edge technology, after all. Obviously though, the outlook should improve significantly as the next generation progresses - and prices do tend to drop significantly over time.