TL;DR
Generally, a standard USB device cannot directly read data from a PC’s internal hard drive when the computer is completely powered off. However, it’s possible under specific circumstances – if the PC is in sleep/hibernation mode or has features like Wake-on-USB enabled, or if special hardware/software configurations are used.
Understanding Why
When a PC is fully turned off, power to most components, including the hard drive and USB controllers, is cut. Without power, data cannot be read or written. A USB device needs power from the computer to operate and communicate with any internal hardware.
How Data Access *Can* Happen
- Sleep/Hibernation Mode: If your PC is in sleep or hibernation mode (not fully off), some components remain powered, including enough of the USB controller and potentially the hard drive to allow limited access. This isn’t a full power-off scenario.
- Check Power Options in Windows Control Panel to confirm if your PC actually shuts down completely when you select ‘Shut Down’.
- Wake-on-USB: Some motherboards support Wake-on-USB, allowing a connected USB device to wake the computer. During this process, the hard drive spins up and becomes accessible.
- This feature is usually enabled in the BIOS/UEFI settings of your motherboard. The exact location varies depending on the manufacturer. Look for options related to ‘Power Management’ or ‘USB Wake Support’.
- Bootable USB: A USB drive can be used as a boot device, allowing you to start the computer from it. This bypasses the internal hard drive and operating system.
- You need to configure your BIOS/UEFI to prioritize booting from the USB drive.
- Example BIOS setting change: Boot Order -> First Boot Device -> USB Drive
- Special Hardware/Software: There are specialized hardware devices and software solutions designed for data recovery or forensic purposes that can access hard drives even when the computer is off. These typically involve direct connections to the drive’s interface (SATA, NVMe) and bypass the standard USB controller.
- These tools are usually expensive and require technical expertise.
Checking if Your PC is Truly Off
- Power Light: A completely off computer should have no power lights illuminated (except potentially a standby light).
- Windows Power Options: In Windows, go to Control Panel > Hardware and Sound > Power Options. Check the settings for ‘Choose what closing the lid does’ and ‘Choose what the power buttons do’. Ensure that ‘Shut down’ is selected, not ‘Sleep’ or ‘Hibernate’.
- BIOS/UEFI Settings: Check your motherboard’s BIOS/UEFI settings to see how it handles shutdown. Some motherboards have options to keep certain USB ports powered even when the computer is off.
- Accessing the BIOS/UEFI usually involves pressing a key (Del, F2, F12, Esc) during startup. The specific key varies depending on your motherboard manufacturer.
Security Considerations
If you’re concerned about data security, it’s crucial to ensure that your computer fully shuts down when selected and that Wake-on-USB is disabled if not needed. Leaving a PC in sleep/hibernation mode or with Wake-on-USB enabled can create vulnerabilities.
Troubleshooting
- Test with Different USB Ports: Try connecting the USB device to different USB ports on your computer. Some ports may provide more power than others.
- Try a Different USB Device: The USB device itself might be faulty or not compatible with your computer.