Sometimes when a state transition is made, the transition itself takes 1usec to run, but other times it doesn't. Maybe I'm misunderstanding something about the correct behaviour. For example, at the start of every boot, a process gets spawned and is moved to running, which starts at 0usecs and finishes at 5usecs. This means that at 0usecs, the transition "starts." Then from the start of t=1usec to the end of t=5usecs, it actually does the transition. This equals 6usecs total. Another example is shown in the picture I've attached. In the first transition shown, the CPU is idle at 115usecs, it starts the transition from sleeping to ready at 116usecs, and actually transitions from 117usecs to 126usecs. Here, the transition takes 11usecs in total, instead of 10usecs. However, in the second transition, the OS is computing at 126usecs. At the exact same time, it starts the transition from ready to running. Then it actually transitions between 127usecs and 131 usecs. Thus, it doesn't take 1usec to start, and the transition takes 10usecs like I'd expected. I'm not sure if the sample is wrong or not. If it is correct, what is the difference between these transitions? Why does one take up 1usec to start while the other doesn't? What is the rule for determining if a transition will take time to start or not?