The SAT is a general knowledge/skill test. There's a math section (if memory serves, algebra and geometry, but not trig or calculus) and a language section (reading comprehension, vocabulary. There is an optional essay portion. Each of the 3 sections is weighted the same (800 points, so total of 1600 default, 2400 if you include the essay).

A-Levels are subject exams. They more closely align to AP exams in the US.