In the first part of this blog series on In Memory Databases (IMDBs) I talked about the definition of “memory” and found it surprisingly hard to pin down. There was no doubt that Dynamic Random Access Memory (DRAM), such as that found in most modern computers, fell into the category of memory whilst disk clearly did not. The medium which caused the problem was NAND flash memory, such as that found in consumer devices like smart phones, tablets and USB sticks or enterprise storage like the flash memory arrays made by my employer Violin Memory.

There is no doubt in my mind that flash memory is a type of memory – otherwise we would have to have a good think about the way it was named. My doubts are along different lines: if a database is running on flash memory, can it be described as an IMDB? After all…