RAM - Random-Access Memory.
High-Level Function: Store program variables, and the program itself.
Low-Level Function: The Stack, and the program itself.
Both the high-level and low-level function are the same, they are just represented differently.
I would say, with overclocking, RAM is probably the biggest blockade. One of the problems with adding more RAM is direct addressing - programs would have to be converted to higher digits to facilitate the increase in RAM.