That (tl;dr: abstractions) and unexpected concurrency. An example story: my aunt asked me to fix her laptop because it was “dead slow”. The usage pattern was to

That (tl;dr: abstractions) and unexpected concurrency. An example story: my aunt asked me to fix her laptop because it was “dead slow”. The usage pattern was to open it, suffer through minutes of delays, do the job and close it again. The way we “fixed” it was to leave it awake for few days so that all defrag, defender, update, prefetch, etc, etc finally did their job without extra interference or interruption. It helped for a while until she received a new ssd disk which we mounted and that solved all issues. Back in the day, run loops always included some form of STI, HLT. Modern computers try to do too much in parallel without being asked to.