This is the number of clock ticks, in 10-millisecond units, a specific CPU has spent on the interrupt stack since the system was booted. An administrator monitors this to detect excessive interrupt-driven overhead on a CPU, which can be a sign of a malfunctioning device generating too many interrupts. For example, a CPU showing unusually high vmsModeInter ticks compared to its peers could point to a failing network adapter or disk controller flooding it with interrupts.