Fix ReadyBoost Caching No Longer Improving Boot Speed on Windows 11

You have used ReadyBoost with a USB flash drive to speed up Windows 11 boot times, but recently the improvement has disappeared. This problem usually occurs after a Windows Update changes how the system handles external caches or after a driver update resets USB controller settings. The ReadyBoost cache may still show as configured, but the system is not using it effectively during boot. This article explains why the cache stops working and provides specific steps to restore boot speed improvements.

Why ReadyBoost Stops Improving Boot Speed After Updates

ReadyBoost works by using a USB flash drive as an additional memory cache. Windows writes frequently accessed boot files to the drive. When the system reads from the cache during startup, it can bypass slower hard drive reads. The improvement is most noticeable on systems with a mechanical hard drive and limited RAM, typically 4 GB or less.

Several events can break this caching mechanism. A Windows Update may change the Superfetch or SysMain service behavior. The service manages the ReadyBoost cache. If the service stops or its startup type changes from Automatic to Manual, the cache is no longer populated during boot. Another common cause is a USB driver update that enables selective suspend. This feature turns off the USB port after a period of inactivity. When the system boots, the port may not wake in time for ReadyBoost to read the cache. A third cause is a file system error on the USB drive. The cache file, EMDMgmt, becomes corrupted and Windows ignores it.

Steps to Restore ReadyBoost Boot Acceleration on Windows 11

1. Check ReadyBoost status on the USB drive
   Insert the USB flash drive. Open File Explorer. Right-click the drive and select Properties. Go to the ReadyBoost tab. If it shows “This device cannot be used for ReadyBoost,” the drive does not meet the minimum speed or capacity requirements. ReadyBoost requires at least 256 MB of free space and a 4 KB random read speed of 2.5 MB/s. If the status shows “ReadyBoost is currently turned off,” click Dedicate this device and then Apply. This forces the cache to use the entire device as a dedicated cache file.
2. Verify the SysMain service is running
   Press Win + R, type services.msc, and press Enter. Find SysMain in the list. Double-click it. If the Startup type is not Automatic, change it to Automatic. If the Service status is Stopped, click Start. Click Apply and OK. Restart the computer and check if boot speed improves.
3. Disable USB selective suspend
   Open Control Panel. Go to Hardware and Sound > Power Options. Click Change plan settings next to your active power plan. Click Change advanced power settings. Expand USB settings > USB selective suspend setting. Set it to Disabled for both On battery and Plugged in. Click Apply and OK. This keeps the USB port powered during boot.
4. Reformat the USB drive and reconfigure ReadyBoost
   Open File Explorer. Right-click the USB drive and select Format. Choose NTFS as the file system. Quick format is fine. Click Start. After formatting, right-click the drive, go to Properties > ReadyBoost. Select Dedicate this device and click Apply. Windows creates a fresh cache file on the empty drive.
5. Run the System File Checker to repair system files
   Open Command Prompt as administrator. Type sfc /scannow and press Enter. Wait for the scan to complete. If corrupted files are found, restart the computer. Then test ReadyBoost again.
6. Check for driver conflicts in Device Manager
   Press Win + X and select Device Manager. Expand Universal Serial Bus controllers. Right-click each USB Root Hub and select Properties. Go to the Power Management tab. Uncheck Allow the computer to turn off this device to save power. Repeat for all USB Root Hub entries. Restart the computer.

If ReadyBoost Still Does Not Improve Boot Speed

“ReadyBoost is currently turned off” message returns after reboot

This happens when Windows sees the cache file as invalid. Open an elevated Command Prompt and run chkdsk E: /f where E is the USB drive letter. This repairs file system errors. After the check, reconfigure ReadyBoost on the Properties tab.

Boot time increased after enabling ReadyBoost

The system may be spending extra time initializing the USB device during POST. Enter the BIOS or UEFI firmware settings. Look for USB boot priority or legacy USB support. Set USB boot to Disabled if you do not boot from USB drives. This reduces the time the firmware spends enumerating USB devices.

ReadyBoost tab shows “This device does not have the required performance characteristics”

The USB drive is too slow. Test with a different flash drive. ReadyBoost requires a 4 KB random write speed of 1.75 MB/s and a 4 KB random read speed of 2.5 MB/s. Most modern USB 3.0 drives meet this requirement. If the drive is older than 2015, replace it.

ReadyBoost Cache vs SSD Upgrade: Boot Speed Comparison

Item	ReadyBoost Cache	SSD Upgrade
Cost	Free to low cost (uses existing USB drive)	Moderate to high cost
Boot speed improvement	Moderate (10-30% faster on HDD systems)	Significant (50-300% faster)
Installation complexity	Plug and play, no hardware changes	Requires opening the PC and cloning or reinstalling Windows
Effect on systems with SSD	No improvement, cache is slower than the SSD	Already optimal
Reliability	Can stop working after updates	Stable and consistent

ReadyBoost remains a useful free option for older computers with a mechanical hard drive and 4 GB of RAM or less. On modern systems with an SSD, ReadyBoost provides no benefit. If you have a desktop PC, consider replacing the hard drive with a SATA SSD for a permanent boot speed improvement. On a laptop that cannot be upgraded, verifying the SysMain service and disabling USB selective suspend will keep ReadyBoost working after future updates.