the Simplicity of noSql

A common stated cause is that noSql is faster than Sql bc it's in memory. From a practical viewpoint, this appears to be the main cause.

But, let's talk theoretical: why can't we put an entire relational db in memory

[It sounds to me that the real cause of the performance of noSql is that it uses a simplified set of instructions/that developers have figured out that's all it's needed for that application, thus allowing it to be placed mainly in volatile memory]


http://stackoverflow.com/questions/5329613/relational-db-in-memory

How much gigabyte expandibility should I have?

Of course it depends on your app or the type of memory; but is 8GB max enough for a 64bit os? Some Dells desktops go up to 192GB. Some 72, some 24, some 48, 16, etc. I need a matrix of apps/memory type/quantity of memory. Can someone do this for me?