How do colleges calculate GPA?

I'm just wondering, how do college calculate high school GPA? Do they calculate it based on the A, B, C scale, ignoring the numerical value? So like even if you have a high A in a cl, like a 98, you just receive a 4.0 for that cl versus a 4.8. Or do they calculate it based on the numerical value? So if you have a 98 in a cl, you receive a 4.8 for that cl.