[naasking]

Sure, you can force a fiction of O(1) by dramatically increasing latency and strictly limiting the size of memory, as we do with microcontrollers. This would now be O(1) with a very large constant factor overhead, basically pinning memory access to the latency of the memory cells that are furthest from the CPU.

[gpderetta]

If there is an upper bound on the latency then it is constant no matter how you look at it.

[naasking]

I'm not disputing you can establish an upper bound on latency. You can always do this by using a system's slowest component as the upper bound and pin everything else's latency to that bound, as I said. I'm just pointing out that this upper bound a) doesn't scale well/leaves a lot of performance on the floor, and b) the upper bound is very sensitive to size and geometry.

In high performance systems, constant time random access is just not constant.