[bluGill]

Any cpu with a cache cannot do it because you are not sure if the data is in cache and will arrive on time or not. If there is something else on the bus (USB, video, network...) you need to design the whole system to ensure that the cpu gets the bus when it needs it regardless of other uses - most computers are not designed this way. A multitasking cpu generally cannot do this because you cannot be sure some other process isn't using the cpu when you need something.

That isn't to say it can't be done. Audio is very time sensitive and Linux does it well with the right kernel options. (video is easier, though it uses far more cpu and data on the bus, it is less sensitive to delay).

Depending on how bad delay it might or might not work. As rule though most real time control is run by low speed 8 bit cpus that have exact timing. You have a high power cpu doing the calculations and then the microcontroller just runs the result of the calculations checking in for new orders as needed.