Retention has always been configurable. As has been repeatedly said, speed and endurance are the primary targets. From there, the model gets tweaked to get the desired compromise.
From the Technology tab on the 4DS website:
Speed is everything in the space close to DRAM, while reaching an endurance as close as possible to DRAM is the opportunity, especially if this reduces the need for more expensive DRAM in systems. Whatever retention this results in may be acceptable. The main reason that retention is far less critical than speed and endurance is the space close to DRAM is that DRAM is essentially a volatile memory. Its contents need to be read and written back (refreshed) every 60 milliseconds and any retention better than DRAM saves power. The reality is that a Storage Class Memory with a retention of just one day is an astonishing 1.5 million times (or 6 orders of magnitude) better than DRAM retention. A Storage Class Memory with a retention of 1 week, 1 month, or 1 year further boosts this to 10 million, 44 million, and half a billion respectively.
The biggest opportunities are always where the pain is the highest and that is in the space closest to DRAM. The ultimate market demand is therefore for Storage Class Memory with DRAM speed, the highest endurance achievable with this speed, a cost per gigabyte closer to NAND Flash, and a pragmatic retention far superior to DRAM retention.
And from last July's investor presentation:
PARAMETERS NEEDED MET. Scales to geometries needed for high-density memory and 3D Endurance has moved into the tens of millions of cycles Read speed comparable to DRAM – an area-based ReRAM first No need for speed crippling error correction – a ReRAM first 4DS Interface Switching ReRAM has displayed enough relevant and meaningful data in each category Endurance far exceeds NAND Flash Retention data adequate for Storage Class Memory
