Any interrupt driven OS needs wait states and they do not slow the machine down if they do not miss the interrupt. It is simply the way they direct traffic when you have more than one thing going on at a time. Generally they are waiting for a hardware event to finish. It can be a problem if you are not managing your hardware efficiently but the biggest time killer is a lack of RAM when the system has to page software segments in and out of disk storage to run. I have seen systems so overloaded that they were paging, just sitting on the desk top.
