With SATA out of the way, you can now easily scale bandwidth by simply adding PCIe lanes. You can remove the middle man by sticking a native PCIe controller on the SSD controller. The SATA interface will talk to the host’s SATA interface, which inevitably sits on a PCIe bus. The SATA side has been limiting max sequential transfers for a while now at roughly 550MB/s. You can view a traditional SSD controller as having two sides: one that talks to the array of NAND flash, and one that talks to the host system’s SATA controller. Rather than wait for another rev of the SATA spec, SSD controller makers started eyeing native PCIe based controllers as an alternative.
Today that number is roughly 500MB/s for 6Gbps SATA, which even value consumer SSDs are able to hit without trying too hard. The result is a setup that can quickly exceed the maximum bandwidth that SATA can offer. A good controller will be able to have reads/writes in flight to over half of those die in parallel. A 256GB SSD can be made up of 32 independent NAND die, clustered into 8 discrete packages. Not only do solid state drives offer amazingly low access latency, but you can hit amazingly high bandwidth figures by striping accesses across multiple NAND Flash die.
Hard drives were rarely quick enough to need more than they were given to begin with, and only after generations of platter density increases would you see transfer rate barriers broken. In the old days, increasing maximum bandwidth supported by your PATA/SATA interface was always ceremonial at first.
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