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There is no documented, general-purpose macOS switch for enabling every CPU core. macOS schedules work across available cores automatically, so an idle core in Activity Monitor does not mean it is disabled. To check for a genuine discrepancy, identify your Mac, compare its active logical processor count with what you expect, and seek diagnosis if the count remains unexpectedly low.
First, distinguish idle cores from inactive cores
A core can be available to macOS without being busy at a particular moment. The operating system schedules work according to what applications need; a light workload may not use every core. Apple explains that macOS schedules work onto appropriate Apple silicon cores based on current performance requirements in its WWDC20 explanation of Apple silicon’s system architecture.
That is different from macOS reporting fewer active processing cores than expected. Apple defines the active processor count as the number of active processing cores available to the computer. It is an operating-system count, so do not automatically equate it with the number of physical cores on every processor design. See Apple’s activeProcessorCount documentation.
Check how many logical processors macOS reports
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Identify your Mac model and processor in Apple menu > About This Mac. You can also open System Information to review hardware details.
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Open Terminal from Applications > Utilities > Terminal.
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Run this command:
sysctl -n hw.logicalcpu -
Read the number printed in Terminal. Apple documents this value as equal to
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The command checks the count macOS reports; it does not show whether each processor is currently busy. Compare the result with the specifications for your exact Mac model and chip rather than using a generic expected number.
Understand how macOS uses cores
Apple silicon
Apple silicon Macs have performance cores for demanding work and efficiency cores for less CPU-intensive tasks. macOS chooses where to schedule work based on performance requirements. An application that does not have enough parallel work may leave some cores idle; there is no user-facing setting to force every performance core to remain active.
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For developers, Apple’s guidance is to use Grand Central Dispatch (GCD) to distribute parallel work and set appropriate quality of service (QoS). Those are application-development techniques, not a system-wide core toggle.
Intel Macs
macOS also schedules work across available processors on Intel Macs. Apple’s separate macOS Server performance-mode instructions are narrowly for Intel Macs running macOS Server and high-performance services; they are not a general consumer setting for enabling cores.
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Choose a power mode only if performance is the issue
Power modes affect energy use and workload behavior, not whether CPU cores are enabled. Apple says Automatic is the default. Low Power Mode reduces energy use, while High Power Mode may improve performance for intensive workloads on listed supported models and can increase fan speeds. Availability depends on the Mac model and macOS version. Apple’s About Power Modes on your Mac page, published June 5, 2026, has the current eligibility details.
On macOS Ventura or later, Apple directs users to System Settings > Battery > Energy Mode; on desktop Macs, the relevant pane is System Settings > Energy > Energy Mode. Older macOS versions may use System Preferences instead. If the option is unavailable, your Mac or operating-system version may not support it.
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| Mode | Purpose | What it means for cores |
|---|---|---|
| Automatic | Default mode; macOS balances energy use and performance. | Does not enable or disable cores as a user-facing switch. |
| Low Power | Reduces energy use. | Changes energy and workload behavior, not core availability. |
| High Power | May improve performance for intensive work on supported models; may increase fan speeds. | Is not a command to activate every core. Availability depends on model and macOS version. |
Do not use server performance mode as a core-unlocking fix
Apple’s macOS Server performance-mode instructions, published December 4, 2023, apply only to Intel Macs and high-performance services using macOS Server. For OS X El Capitan 10.11 and later, Apple documents setting the NVRAM boot-args variable; changing performance mode requires a restart. This specialized server feature is not a documented way to enable all cores on an everyday Mac, so do not apply it as a general troubleshooting step.
Get help if the active count is persistently lower than expected
Apple lists boot arguments, thermal throttling, and a manufacturing defect as possible reasons a core may not be active. A CPU graph alone cannot tell you which, if any, applies. If the Terminal count remains unexpectedly low after you have confirmed the Mac model and checked ordinary power behavior, contact Apple Support or a qualified service provider for diagnosis. Avoid undocumented boot arguments or third-party utilities claiming to unlock cores; the cited Apple guidance does not establish them as a general solution.
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