Why do you use "much" when mentioning RAM?

Solution 1:

Quantifying is not the same as counting.* You can say "2 litres of water", but that doesn't mean it's countable (it's not). Similarly, you can say "2 GB of RAM", but not "I need 2 RAMs in my phone": it's not countable. That's why you don't ask "how many RAMs do I need for this?", but rather:

How much RAM do I need?

The word "GB" is obviously countable, though: written in full it would be "Gigabytes", abbreviated as GB (we tend to leave out plural endings when counting abbreviated units, cf. "2 l, 10 m, 7 kg").

*) I got to start with a capital q!

Solution 2:

Think of RAM as being like a bowl of sand. You would say 'How much sand is there here?', but 'How many grains of sand are there here?'. Similarly 'how much RAM', but 'how many GB of RAM'.