"High compression memory" is immersion-breaking magic. There are hard mathematical limits to how much you can compress things (Kolmogorov complexity), and every lossless compression algorithm necessarily increases the size of some inputs (pigeonhole principle). It's much simpler to assume that "M" is slang for some bigger unit.

We already have the real life example of people using "mega" (10^6) as slang for "mebi" (2^20).