[ajanuary]

Right, which makes it a bit of a tricky attack to pull off. But if you know what you're doing you can do some operation that requires memory address x and be reasonably sure it will end up in the CPU cache. If you then do an operation on memory address x, and it happens really quickly, and you do an operation on memory address x+128, and it happens a bit slower, you can assume that x was in the cache and x+128 wasn't.

[samsonradu]

Yes, I got the part where you can time if memory address X is in cache and X+128 isn't. But how does one read the data at memory address X?

[ajanuary]

You load it into a register. If you're trying to drive it from a high level language, I guess you can do something like an add which will get compiled into instructions to load it into a register first.