Why Windows Task Manager Can Feel Wrong About CPU Usage, According to Its Original Creator

If you have ever opened Windows Task Manager during a lag spike and thought, "Eh, why does this number feel off?", turns out you are not imagining things.

Former Microsoft engineer Dave Plummer, the guy who built the original Task Manager, recently explained why CPU usage is much harder to measure than most people think. Plummer is also known for work on Windows features like ZIP file support and the Windows NT Start Menu, so this is not some random hot take from the internet. He literally built the tool.

His main point is simple: CPU usage sounds easy to explain, but it really is not. On paper, you would think a PC should just tell you how busy the processor is and be done with it. In reality, that opens up a lot of messy questions. Is the CPU busy on one core or all cores? Are we talking about a single instant, or an average over the last second or two? Does "busy" include user work, kernel work, interrupts, deferred procedure calls, or other low-level system activity?

That is why Task Manager does not give you a perfect live reading. According to Plummer, the original Task Manager was built to stay extremely lightweight so it would not waste precious system resources. It was also timer-driven, meaning it refreshed at intervals and showed an interpretation of what happened between those refreshes, not a true real-time snapshot.

The obvious shortcut would have been to take CPU usage and divide it by the time between updates. But Plummer said that approach depends too much on the interface timer firing exactly when it should. In other words, if the timer itself is a bit inconsistent, your usage reading also becomes shaky.

So he used a different method.

Instead of asking, "How busy is the CPU right now?", Task Manager looks at the total CPU time used by each process since it started. That total includes both kernel time and user time. Then, on the next refresh, it compares the new total against the previous one for that same process. The difference tells Task Manager how much CPU time that process consumed during that specific period. After that, it divides the value against the total CPU time accounted for across all processes between refreshes.

Yeah, a bit more mafan than a simple percentage, but also more accurate for the job it was designed to do.

The bigger problem is that modern CPUs have changed a lot since the original Task Manager was built. Back then, time spent on the CPU was a decent approximation of work done. Today, that link is much weaker. Modern processors constantly adjust themselves with dynamic frequency scaling, turbo boost, thermal throttling, and deep idle states. A CPU running for the same amount of time can deliver very different levels of actual performance depending on its clock speed and conditions.

That is why a usage number can feel "slippery" on modern hardware. Your CPU might show a certain percentage, but that does not fully capture how much real work is getting done. Plummer compared it to traffic on a freeway: a half-full road with fast cars can still move more traffic than a packed road full of slow trucks.

For Malaysian and SEA PC users, this matters more than you might think. If you game on a laptop in our panas weather, or use a budget gaming rig that is constantly juggling heat and power limits, CPU percentages alone do not always tell the full story. The same goes for streamers, esports players, and anyone troubleshooting stutter in games like Valorant, CS2, Dota 2, or Apex. Sometimes the number looks "fine", but boost behaviour, throttling, or uneven per-core loads are the real problem.

Plummer even said that, in an ideal world, CPU usage should measure the amount of work completed versus the theoretical maximum work the chip could have done. That would be a much better reflection of real performance, but he also admitted he is retired now, so it is not like he gets to redesign Windows from the couch.

If nothing else, this is a nice reminder that Task Manager is useful, but not magical. If the CPU graph feels weird, it does not automatically mean Windows is broken. Sometimes the hardware itself is just too complex for one neat percentage to explain properly.

Source: Tom's Hardware