It's worth noting that in current conditions the assumptions may be unwarranted. First, while storage used to be orders of magnitude slower than memory, not SS

It's worth noting that in current conditions the assumptions may be unwarranted. First, while storage used to be orders of magnitude slower than memory, not SSD storage is just a single order of magnitude slower; Second, in many domains now it's often practical to ensure that your data set can fit in memory. For example, if your system is for storing financial transactions (which is a prime market for Oracle), then your enterprise has to be quite large to get a terabyte of transactions and you can put a terabyte (or much more) of RAM in a database system if you choose to.