System Interrupts are a mechanism by which the hardware (or a background device) can notify the processor that something requires attention, could be USB transfer, disk transfer something like that; nothing to worry about.
Even simply moving your mouse activates an interrupt, the Operating System see’s the interrupt which tells it that the mouse is being used and it must divert it’s attention to what the mouse is doing.
If your old processor is struggling to keep up with newer software this can occur more often, the reason everyone is saying replace the machine is due to its age and it being more cost and time effective than solving the issue on the older machine.
Performing a clean install of Windows is a shortcut in troubleshooting the software issues, as you start to reinstall all of your programs the culprit with either show it’s head once you install the software or the problem will correct itself due to the clean installation and not running an operating system that once was windows 8.
Tap or click here for a thread on system interrupts from Microsoft.
Tap or click here for more info on system interrupts on Wikipedia.