Crypto · The Register
Task Manager's CPU meter is an obituary for the recent past, tells the engineer who created it
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Windows has always had a built-in portal to the recent past: Task Manager's CPU usage meter.
Key facts
- Windows has always had a built-in portal to the recent past: Task Manager's CPU usage meter
- The CPU number in Task Manager is a moving little obituary for the immediate past," explained former Microsoft engineer Dave Plummer, "Not what happened at the moment that your eyeballs landed
- For an individual process, the math is the cumulative current CPU time minus the previous cumulative CPU time
- Petzold" refers to the books by Charles Petzold, which were an indispensable companion to Windows programmers in the 1990s, well into the 2000s
Summary
"The CPU number in Task Manager is a moving little obituary for the immediate past," explained former Microsoft engineer Dave Plummer, "Not what happened at the moment that your eyeballs landed on the row. Plummer wrote the original version of Task Manager, back when it was a lean, mean, process-killing machine rather than the considerably chubbier and cuddlier tool of today. So how did Task Manager report the CPU percentage? Every time the timer fired, the code asked the kernel for cumulative execution times and compared them to the previous sample. "For an individual process, the math is the cumulative current CPU time minus the previous cumulative CPU time.