This is the total clock ticks, in 10-millisecond units, all CPUs combined have spent on the interrupt stack since the system was booted. An administrator uses this system-wide figure to detect an overall rise in interrupt-driven overhead across the machine, which individual per-CPU vmsModeInter values might mask if spread unevenly. For example, a steadily climbing vmsTotalInter trend would prompt the administrator to check per-CPU interrupt figures to find which device or CPU is driving the increase.