To set CPU affinity in Windows 10 or 11, open Task Manager, go to Details, right-click the app’s process, choose Set affinity, and select the logical processors it may use. This restricts where the process can run; it does not automatically make an app faster. Test the change under the same workload and restore All processors if performance gets worse.
For a one-time change, use Task Manager. To launch an app with a mask, use Command Prompt’s start /affinity; for a script, PowerShell exposes the process’s ProcessorAffinity property. These changes generally apply to a process instance, not permanently to the application.
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What CPU affinity does in Windows 10/11
Windows schedules threads across logical processors. Process affinity restricts the logical processors on which a process’s threads are allowed to run. It does not make the process use every selected processor continuously.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallA logical processor is what Windows presents as a CPU number. It may be a physical core or a simultaneous-multithreading (SMT) thread sharing a physical core with another logical processor. CPU 0 therefore does not necessarily mean one whole physical core in the performance sense.
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Affinity is a restriction, not an automatic performance boost. Microsoft generally cautions against forcing affinity because doing so can interfere with the scheduler and limit parallel processing. It can be useful for controlled tests, isolating a background workload, troubleshooting, or a deliberate CPU-topology experiment. Microsoft’s processor-affinity guidance explains the trade-offs.
Affinity is different from CPU priority, which affects scheduling urgency; power mode, which affects system-wide power and performance behavior; and core parking, which is governed by Windows power management. Windows also has CPU Sets, a more flexible mechanism intended to cooperate with power management, but they are mainly an advanced API concept rather than a simple Task Manager setting. Microsoft’s CPU Sets documentation has details.
When you should try affinity
Affinity is most defensible when you are testing a scheduling issue, isolating a background render or encoding task, working around a legacy application, benchmarking, or experimenting with hybrid CPU cores. It is unlikely to help if the app is GPU-limited, the processor is lightly loaded, or the real problem is memory, storage, heat, drivers, network latency, or the application itself.
Restricting a game or multithreaded app to too few processors can lower frame rates, increase frame-time variation, or slow completion. Change one setting at a time, measure the result, and keep a way to undo it. Do not treat CPU affinity as a substitute for CPU priority or use real-time priority casually.
Before you change anything
- Find the actual workload process. Many apps create launchers, helpers, anti-cheat services, or worker processes. In Task Manager’s Details tab, check the CPU column while the app is active; do not assume the launcher is doing the work.
- Check the CPU topology. Task Manager’s affinity choices represent logical processors, not necessarily physical cores. On hybrid Intel CPUs, numbering is not a universal P-core/E-core map. On AMD processors with SMT, processor numbering does not reliably identify physical-core siblings. Verify your particular system’s topology before selecting processors.
- Record a baseline. Compare the same workload before and after. For games, check frame rate and frame-time consistency; for rendering or encoding, compare completion time; for interactive apps, assess responsiveness.
- Avoid changing critical Windows processes casually. Some protected or elevated processes may reject a change, and restricting system processes can cause problems.
Method 1: Set CPU affinity from Task Manager
Task Manager is the quickest way to test affinity on a running process. The exact layout can vary slightly by Windows version.
- Press Ctrl + Shift + Esc to open Task Manager. Choose More details if that option appears.
- Open the Details tab.
- Find the app’s executable process. Check the CPU column while the app is active to help identify the process doing the work.
- Right-click the process and select Set affinity.
- In the Processor affinity window, clear All processors, then select the logical processors to allow.
- Select OK, then check the process again after a short time to confirm the change was accepted.
For a protected, elevated, or other-account process, you may need to run Task Manager as administrator. A Task Manager change generally affects only that running process instance; it is not a permanent profile for future launches.
Restore unrestricted scheduling
- Open Set affinity for the process again.
- Select All processors, then select OK.
Method 2: Launch an app with Command Prompt
Windows 10 and 11 support the start /affinity command. Its mask is hexadecimal: each set bit permits the corresponding logical processor. When the executable path is quoted, the first empty quoted argument is the window-title placeholder.
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Allow logical processors 0–3: start “” /affinity F “C:\Games\Example\game.exe”
Allow logical processors 0–7: start “” /affinity FF “C:\Apps\Example\app.exe”
Allow logical processors 0 and 2: start “” /affinity 5 “C:\Apps\Example\app.exe”
The mask applies when the new process starts; it does not create a permanent setting for every future launch. If you normally start an app through Steam, Epic Games, or another launcher, make sure you are targeting the executable that does the work and preserve any required launch arguments. The Microsoft start command reference documents the syntax.
Method 3: Set affinity with PowerShell
PowerShell’s .NET System.Diagnostics.Process.ProcessorAffinity property sets the affinity mask for a process instance. Replace the example process name with the executable name without “.exe”; if multiple instances match, the pipeline example applies to each one.
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Set affinity for one matching process, allowing logical processors 0–3: $process = Get-Process -Name “app”; $process.ProcessorAffinity = [IntPtr]0xF
Set affinity for every matching process: Get-Process -Name “app” | ForEach-Object { $_.ProcessorAffinity = [IntPtr]0xF }
Inspect the current mask: (Get-Process -Name “app”).ProcessorAffinity
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteTo launch an app and then set affinity, use: $process = Start-Process “C:\Path\To\App.exe” -PassThru; Start-Sleep -Seconds 2; $process.ProcessorAffinity = [IntPtr]0xF
The delay gives the process time to start, but some apps hand work to a different process. Verify the actual CPU-consuming process and apply the change there if needed. Access-denied errors can occur with protected or elevated processes. A 64-bit PowerShell session is the usual choice on modern Windows systems, especially on machines with many logical processors. This setting is for the current process instance, not a permanent application profile. See the .NET ProcessorAffinity documentation.
Method 4: Use Process Lasso for persistent rules
A third-party process-management utility such as Process Lasso can apply configured rules when a process starts. Use a persistent rule only if repeated testing shows it helps; a rule can keep reapplying a restriction after a relaunch.
- Install and open the utility.
- Launch the target app and locate the process that does the work.
- Create an affinity rule for that process and select the desired logical processors.
- Enable the rule, then test the app after a fresh launch.
- To undo the change, remove or disable the rule and restore All processors if necessary.
Picking processors and calculating the affinity mask
A mask is a bitmask, not a count of CPUs. Each bit position corresponds to a logical processor index; bits set to 1 are allowed. The table shows the hexadecimal mask for common selections.
| Selection | Hex mask |
|---|---|
| CPU 0 only | 1 |
| CPU 1 only | 2 |
| CPUs 0–1 | 3 |
| CPUs 0–3 | F |
| CPUs 0–7 | FF |
| CPUs 0 and 2 | 5 |
For example, CPUs 0–3 set bits 0, 1, 2, and 3, giving binary 1111 and hexadecimal F. That is why start /affinity F allows four specific processors; the mask is not simply the decimal number of processors selected.
There is no universal best mask. For a single-threaded app, one CPU may be useful for a controlled test but can also become a bottleneck. A multithreaded app may need a broader set. Do not assume a contiguous range means P-cores, or that alternating indices map to physical cores; verify the topology on your own system.
Edge cases and gotchas
More than 64 logical processors
This is unusual on consumer systems. On Windows 11 and Windows Server 2022, processes and threads span processor groups by default on systems with more than 64 logical processors. Legacy APIs and applications that explicitly manage processor groups may behave differently. If this applies to your system, verify the tool and application’s group behavior rather than assuming a simple mask covers every processor. See Microsoft’s processor-groups documentation.
Child processes and launchers
Setting affinity on a launcher does not guarantee that the worker process doing the work has the same setting. Some child processes may inherit affinity in some launch scenarios, while launchers, services, or applications may create or configure processes differently. Check the actual process and test.
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Affinity versus priority and power management
Affinity controls where a process may run; priority affects its scheduling urgency. Efficiency mode and EcoQoS are resource-management mechanisms, not affinity controls. Power plans and core parking are separate system power-management behavior. Change one variable at a time so you can identify what helped or hurt. Microsoft’s Task Manager Efficiency mode overview describes that feature.
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Troubleshooting when affinity changes do not stick
The Set affinity option is missing or unavailable
Confirm that you are in Task Manager’s Details tab and selected a normal process. For an elevated or protected process, try Task Manager as administrator. Avoid changing affinity on critical Windows processes.
The change has no effect
Confirm that you selected the process consuming CPU, not just a launcher, and check whether a worker process starts or the app restarts. If the app is GPU-limited or the problem is caused by another bottleneck, affinity may not help.
The app becomes slower, crashes, or will not start
Restore All processors in Task Manager. Remove the affinity argument from a shortcut or batch file, undo the PowerShell script, and disable any persistent third-party rule. Make sure the mask selects available processors. Restart the app; if a launcher keeps applying the setting, restart Windows after removing the rule.
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That is expected for a Task Manager change to a process instance. Use a launch command, script, or third-party rule if testing shows you need the setting reapplied, and remove it if results worsen.
CPU usage is lower, but performance is not better
Lower CPU usage does not necessarily mean better performance. Compare frame times and frame rate for games, completion time for rendering or encoding, or responsiveness for interactive apps. If affinity worsens the result, restore unrestricted scheduling.
Comparison: which method should you use?
| Method | Best for | Limitations |
|---|---|---|
| Task Manager | One-time tests on a running process | Usually applies only to that process instance; manual selection |
| start /affinity | Repeatable launches from a command or shortcut | Requires a correct hexadecimal mask and the right executable |
| PowerShell | Scripts that target process instances | Requires the right process and permissions; not a permanent profile |
| Third-party process manager | Persistent rules reapplied at launch | Requires installing and maintaining a separate utility |
FAQ
Will CPU affinity make my game faster or increase FPS?
Sometimes a specific workload may benefit, but affinity often makes no difference or reduces performance by limiting the scheduler. Test frame rate and frame-time consistency under the same conditions; restore All processors if results worsen.
Does setting an app to one core make it faster?
Not in general. A single processor can bottleneck an app that can use multiple threads. Use one processor only for a deliberate test or a specific compatibility reason.
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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →What does CPU 0 mean?
CPU 0 is the logical processor Windows labels index 0. It may be an SMT thread rather than an entire physical core. On hybrid processors, its number alone does not tell you whether it is a P-core or E-core.
Should I choose P-cores, E-cores, or physical cores?
There is no universal mapping from processor numbers to P-cores, E-cores, or physical-core siblings. Check your system’s topology and measure the workload rather than guessing from the indices.
Does Task Manager affinity persist after restarting the app?
Generally, no. Task Manager changes apply to the current process instance. A launch command or script can reapply affinity when used, while a third-party process manager may provide persistent rules.
How do I undo CPU affinity?
In Task Manager, open Set affinity, select All processors, and select OK. Also remove any launch-command mask, script, or persistent third-party rule that reapplies the restriction.
Bottom line
Use Task Manager to test CPU affinity on the process that actually does the work. For repeatable launches, use a correctly formed hexadecimal mask with start /affinity or apply the .NET process property in PowerShell. Affinity is a constraint, not a guaranteed performance tweak: measure the result and restore All processors if it does not help.
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