Glossary
Thermal state
macOS's rating of how hot the Mac is: nominal, fair, serious or critical.
What it is
macOS tracks a thermal state for the whole system. At nominal and fair, nothing changes. At serious and critical, the system reduces performance to bring temperatures down, which is called throttling.
Apps can read this state through a public API, which is how iKnowMyMac reports it on every Apple silicon Mac, even where individual temperature sensors aren't readable.
Why it matters
Throttling makes everything slower at once, and no single process looks responsible. Knowing the thermal state, and which apps used the most energy while it rose, explains it.
In Activity Monitor
Not shown directly. Apple notes that kernel_task using a lot of CPU is how macOS manages temperature, so a busy kernel_task can be a sign of heat.
In iKnowMyMac
The thermal state on every chip, CPU and GPU temperatures and fan speeds where validated (M1 Pro), and thermal throttling alerts. Diagnosis correlates heat with the top energy users.
pmset -g thermShows whether a thermal or performance warning has been recorded.
Know why your Mac is slow.
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