macOS has no documented general-purpose switch for enabling every CPU core: it schedules work across the available cores automatically. If some cores look idle, that does not mean they are disabled. To check whether macOS reports fewer active logical processors than expected, identify your Mac, run one Terminal command, and use the result to decide whether further diagnosis is needed.
How do I enable all cores on my Mac?
You generally do not need to enable them. Apple describes macOS as scheduling applications onto appropriate cores according to their performance requirements. A core that is not busy at a particular moment is different from a processor that the operating system does not report as active.
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Apple does not document a general user-facing macOS setting to turn on all CPU cores. Avoid treating an idle-looking CPU graph or an undocumented command as evidence that a core needs unlocking.
Step 1: Identify your Mac and clarify what you are seeing
Open Apple menu > About This Mac to check the model and processor. For more detail, open Apple menu > About This Mac > More Info > System Report and review the Hardware information. Menu wording can vary by macOS version.
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Then distinguish between two different observations:
- Some cores show little or no activity: this is a utilization snapshot. macOS schedules work as needed, so a light task may not keep every core busy.
- The active processor count is lower than you expect: this is a count reported by the operating system and is a more relevant check for a possible discrepancy.
Step 2: Check the active logical processor count
- Open Applications > Utilities > Terminal.
- Enter
sysctl -n hw.logicalcpuand press Return. - Read the number printed in Terminal. Apple equates this value with
ProcessInfo.activeProcessorCount, the number of active processing cores available to the computer.
This is an operating-system count of logical processors; do not assume it always equals the number of physical cores. Compare it with reliable specifications for your exact Mac model and chip rather than estimating from an Activity Monitor graph. Apple notes that the active count can vary.
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Why some cores may be idle—or not active
Idle cores are not necessarily disabled
macOS decides where work should run. On Apple silicon, performance cores are designed for maximum-performance work and efficiency cores for less CPU-intensive tasks. The system schedules work according to its performance requirements; an application may not have enough parallel work to keep every core occupied. Apple explains this scheduling model in its WWDC20 overview of Apple silicon architecture.
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A lower active count can have several causes
Apple lists boot arguments, thermal throttling, and a manufacturing defect as possible reasons a core may not be active. A single CPU graph does not reveal which, if any, applies. Apple’s activeProcessorCount documentation defines the count and names these possible factors, but does not provide a consumer diagnostic procedure.
Step 3: Check power mode if the concern is performance
Power modes affect energy use and workload behavior; they are not core-enable controls. Apple says Automatic is the default. Low Power Mode reduces energy use, while High Power Mode may increase fan speeds and can improve performance for intensive workloads on supported models. Availability depends on the Mac model and macOS version.
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On macOS Ventura or later, Apple’s path is Apple menu > System Settings > Battery (or Energy on desktop Macs) > Energy Mode. On earlier systems, look in System Preferences. Check Apple’s current About Power Modes on your Mac page for eligible models and current interface details; it reports publication on June 5, 2026.
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| High Power Mode | May help intensive workloads on supported models; may increase fan speeds | Does not enable cores |
Why server performance mode is not a general solution
Apple’s serverperfmode=1 instructions apply only to Intel Macs and are intended for high-performance services on a Mac running macOS Server. Apple documents setting the NVRAM boot-args variable for OS X El Capitan 10.11 and later, and the change requires a restart. This is a server performance feature, not a method for enabling cores on an everyday Mac. See Apple’s Turn on performance mode for macOS Server page, published December 4, 2023.
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Step 4: Escalate a persistent count discrepancy
If the active logical processor count remains unexpectedly low after checking the model and ordinary power settings, contact Apple Support or a qualified service provider for diagnosis. Apple identifies several possible causes, including a hardware defect, but the count alone cannot establish the cause. Do not try undocumented boot arguments or third-party utilities as a general core-unlocking fix.
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