AOMEI Partition Assistant
What is Partition Assistant Restart Mode?
Partition Assistant offers a special startup environment called PreOS mode. Some specific operations not be completed under the reboot mode. You can read to know more details.
By Dervish / Updated on April 7, 2025
Introduction to PreOS mode
What is PreOS mode? PreOS mode is a special startup environment that AOMEI Partition Assistant uses to perform disk operations before Windows loads. Generally speaking, when you click the "Apply" button to commit an operation and click the "Proceed" button to start on Partition Assistant, the operation will be completed under Windows Mode.
In this mode, there is no need to reboot the computer. As below:
However, some operations—such as "Shrink system partition," "Clone System Partition," or "Migrate OS to SSD"—cannot be completed in Windows Mode, especially when certain applications are running on the target partition or when the system partition cannot be locked. In such cases, the program needs to reboot the computer to complete the task. This is done through Reboot Mode, which includes Windows PE Mode and PreOS Mode.
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Windows PE Mode: This is a lightweight version of Windows used for advanced system tasks like partition management, system repair, or installation. In tools like AOMEI Partition Assistant, it allows operations that can't be done while the main Windows system is running by rebooting into this special environment.
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PreOS Mode (AOMEI-specific): This is a simplified pre-boot environment created by AOMEI itself. It doesn’t require a bootable USB or external setup. When you apply certain changes, AOMEI reboots the system into this mode to perform the operation before Windows loads, then starts Windows as usual.
AOMEI Partition AssistantThe Best Windows Disk Partition Manager and PC Optimizer
Once you click the "Apply" button to commit an operation and click the "Proceed" button to start the process, you will be asked to select a mode, either "Restart into Windows PE mode" or "Restart into PreOS mode" to execute the operation. In this case, you need to select one mode you prefer to execute the operation.
Windows PE Mode
When you select the "Restart into Windows PE mode" option to perform operations, it will first create a WinPE bootable iso based on the system's recovery environment.
After the creation of WinPE is finished, the PC will reboot into the WinPE environment to execute the operation.
After operations are completed, it will reboot into Windows by default.
PreOS Mode
When you select the "Restart into PreOS mode" option to perform operations, there is no need to create ISO, so that it will be faster to enter into PreOS mode to perform operations. For system partitions, we suggest that you select WinPE mode to resize partitions.
The below interface is the PreOS mode in Windows 7 or the below system versions:
The below interface is the PreOS mode in Windows 8 and above system versions:
After operations are completed, it will reboot into Windows by default.
Notes:
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When the program reboots into the WinPE environment and detects system environment changes, it will quit the WinPE environment and then reboot into PreOS mode to continue operations.
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If AOMEI Partition Assistant can't detect the system's recovery Environment due to some reasons, it will only reboot into PreOS mode.
AOMEI Partition AssistantThe Best Windows Disk Partition Manager and PC Optimizer
Manually Enter into PreOS Mode
In order to make the process run under the boot mode, you should hold down the "Shift" key when you click the "Apply" button. Then it will commit the operation under PreOS mode.
