We do, something like http://techreport.com/articles.x/16255 http://techreport.com/articles.x/16255 or http://www.anandtech.com/show/1697/5 http://www.anandtech

We do, something like http://techreport.com/articles.x/16255 http://techreport.com/articles.x/16255 or http://www.anandtech.com/show/1697/5 http://www.anandtech.com/show/1697/5 although I don't think they actually have a full NV backing store. They definitely exist though, and have done even before SSDs, it just had a normal disk hanging off it. Battery-backed cache has probably been around even longer in write caches for large RAID systems. The 5% power and shutdown is also how the Macbook laptops handle sleep. Sleep mode is a low power nothing-but-ram mode, and when the battery gets too low, it goes into 'safe sleep', basically a dump-to-disk all-powered-off hibernate. The main reason it's not all that common is that for the sort of workloads you're prepared to pay for a shitload of RAM, you're probably just using it as a cache for a DB or some monster app, and actually keeping it around isn't that much of a priority. You've got failover somewhere else in the stack, and it's one less thing to buy and maintain. The other critical flaw is that there is a (potentially huge) performance hit in presenting as a disk vs hanging off the northbridge MMU. Even the latest in new fancy SATA is hilariously slow compared to the actual memory bus (6Gbps for SATA3 vs maybe 100Gbps for DDR3[1]), and having all the filesystem abstraction on top, as in the titular article of this thread mentions, is a whole lot more overhead. So yeah. We can. Sometimes people do. But it's probably easier and better to just stick it in the actual RAM slots, and use it differently for everything except 5-second boot times. [1] https://en.wikipedia.org/wiki/List_of_device_bandwidths#Storage https://en.wikipedia.org/wiki/List_of_device_bandwidths#Stor...