The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →If Windows reports that rdyboost.sys is missing, not found, or caused a startup failure, repair Windows’ own component store and protected files rather than downloading a replacement file. In a normally running system, open Command Prompt as administrator, run DISM.exe /Online /Cleanup-Image /RestoreHealth, then sfc /scannow, restart, and install pending updates. If Windows cannot start, run the offline versions of DISM and SFC from Windows Recovery Environment (WinRE), checking the correct Windows volume letter first.
What rdyboost.sys is and why the error matters
rdyboost.sys is the Windows system-driver file for ReadyBoost. Microsoft’s service configuration identifies the service as ReadyBoost, classifies it as a kernel driver, and gives its binary path as SystemRootSystem32driversrdyboost.sys. The expected file is therefore under the Windows system-driver directory, normally C:WindowsSystem32drivers when Windows is installed on drive C.
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A message such as “rdyboost.sys is missing,” “rdyboost.sys not found,” or “What failed: rdyboost.sys” usually indicates that Windows cannot read a protected system file or cannot start the related driver service. The underlying problem can be component-store corruption, damage to protected files, disk errors, or a failed startup repair. It does not automatically mean that ReadyBoost itself is useful or that a separate copy of the file should be installed.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsDo not download a random SYS file from a driver or DLL mirror, and do not copy one from another computer. A file from a different Windows edition, build, architecture, or update level may be incompatible, and an untrusted download creates a security and reliability risk. The supported approach is to repair the Windows image and protected files, then use recovery tools if the computer cannot boot.
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Decide which repair path fits your situation
Use the path that matches both the computer’s boot state and the likely cause. The table keeps the choices separate so that a missing ReadyBoost tab is not confused with a failed system file.
| Situation | Bootability | Likely focus | Repair source | Relative risk |
|---|---|---|---|---|
| Windows starts and shows a rdyboost.sys error | Windows runs | Component-store or protected-file corruption | Windows Update through online DISM | Supported Microsoft commands |
| Windows starts, but the error returns after restart | Windows runs intermittently | Unrepaired corruption, pending updates, or disk errors | DISM, SFC, Windows Update, then disk checks if indicated | Supported commands; back up important files first |
| Windows cannot start | Use WinRE or installation media | Offline system-file or image damage | Offline Windows image; matching installation media if required | More consequential because commands target an offline installation |
| ReadyBoost tab is absent but Windows works normally | Windows runs | Normal feature availability, especially on SSD storage | No file replacement is indicated | Do not force the feature or replace a SYS file |
Repair rdyboost.sys when Windows can start
1. Open an elevated Command Prompt
- Sign in to Windows 11 or Windows 10.
- Open Start and type Command Prompt.
- Choose Run as administrator. Approve the User Account Control prompt.
The commands below must run with administrative rights. If the window title does not indicate an administrator session, close it and reopen Command Prompt with Run as administrator.
2. Repair the Windows component store with DISM
At the prompt, run:
DISM.exe /Online /Cleanup-Image /RestoreHealth/Online tells DISM to service the Windows installation that is currently running. /Cleanup-Image checks the Windows image, and /RestoreHealth attempts to repair corruption. Microsoft explains that DISM normally obtains the repair files through Microsoft Update, so the process can take time and may require a working internet connection.
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Leave the window open until DISM finishes. Do not interrupt the computer by holding the power button while the image is being serviced. If DISM reports that it repaired corruption, continue to SFC; if it reports that no corruption was found, continue to SFC anyway because the two tools check different layers of Windows.
3. Check protected files with SFC
After DISM completes, run:
sfc /scannowSystem File Checker (SFC) checks protected Windows files and replaces missing or corrupted copies when a valid copy is available. Let the scan reach 100 percent. Restart Windows after it finishes, even if the result says that no integrity violations were found, then check whether the rdyboost.sys message has disappeared.
4. Install pending Windows updates
Open Settings > Windows Update on Windows 11, or Settings > Update & Security > Windows Update on Windows 10. Select Check for updates, install the updates offered for your edition, and restart when Windows requests it. If Windows Update reports a problem, use its troubleshooter, restart, and check for updates again. An update can replace damaged system components, but no future update is guaranteed to resolve a particular rdyboost.sys failure.
5. Check the result after the restart
- Sign in normally and repeat the activity that produced the message.
- If the error has gone, avoid downloading a replacement SYS file; the Windows repair has restored the supported file set.
- If the error returns, note whether it appears during startup, when a USB storage device is connected, or after Windows resumes. That timing helps distinguish a startup-file problem from a broader disk or image problem.
When DISM cannot find repair files
Online DISM normally uses Microsoft Update as its repair source. If the command says that source files cannot be found, the installed Windows image may need a local source. Microsoft documents using the /Source option with Windows installation media.
- Obtain Windows installation media that matches the installed Windows edition and build. A source for a different edition or build may not contain the correct component files.
- Connect or insert the media and identify its drive letter in File Explorer or Command Prompt.
- Run DISM again with
/Sourcepointing to the matching image source, following Microsoft’s syntax for the media format you have. Do not substitute a random file path or a SYS file downloaded from the internet. - After the image repair completes, run
sfc /scannowagain and restart.
If you cannot obtain matching media, keep the installation media available for WinRE recovery and resolve the source issue before experimenting with unverified downloads. The objective is to repair the component store, not to replace one file in isolation.
If Windows will not boot
When the normal desktop is unavailable, use Windows Recovery Environment (WinRE) or boot from Windows installation media. The commands are similar to the online procedure, but they must target the offline Windows installation.
1. Start WinRE or installation media
Enter WinRE through the recovery options shown after failed starts, or boot from Windows installation media and choose the repair option instead of installing Windows. If you use a USB drive, it is removable media for starting the recovery environment; it is not a guaranteed rdyboost.sys replacement.
2. Confirm the Windows volume letter
In WinRE, the Windows partition may not be assigned C:. Before running an offline command, identify the volume that contains the Windows directory and use that letter in every command. A letter mismatch can make a valid repair target the wrong volume.
Once you have confirmed the letter, substitute it for C: in the examples below. The examples assume that the Windows installation is on C only to show the required syntax.
3. Run offline SFC
At the WinRE Command Prompt, run:
SFC /scannow /offbootdir=C: /offwindir=C:Windows/offbootdir identifies the boot volume and /offwindir identifies the offline Windows directory. Replace both paths if WinRE assigned another letter. Wait for the scan to finish before closing the recovery console.
4. Run offline DISM
Run the offline image repair:
DISM /image:C: /cleanup-image /restorehealthReplace C: with the confirmed Windows volume. If the offline image cannot obtain repair files, connect matching Windows installation media and use its image as the DISM /Source, selecting media that matches the installed edition and build. The source must correspond to the offline installation; copying rdyboost.sys from another PC is not an equivalent repair.
5. Check the disk when corruption may be recurring
If the file repeatedly disappears, repairs fail, or startup errors suggest disk damage, run:
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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →chkdsk /f /rMicrosoft includes offline SFC, DISM, and chkdsk in recovery guidance when missing or corrupted system files or drivers prevent startup. The /f option requests filesystem repairs and /r checks for unreadable sectors while attempting to recover readable information. Disk checking can take a long time, especially on large or damaged drives. If the files on the drive are important and accessible elsewhere, preserve a backup before undertaking repeated repair attempts.
6. Restart and reassess
Close the recovery tools and restart from the internal drive. If Windows starts, complete the online DISM, SFC, and Windows Update sequence as well; the offline pass may have repaired enough to boot, while the online pass verifies the running installation. If Windows still will not start, record the exact message and whether the failure occurs before or after the Windows logo. Repeating random commands or replacing individual SYS files will not address an incorrect volume, an unmatched repair source, or a failing disk.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A missing ReadyBoost tab is not automatically a missing rdyboost.sys file
Some readers search for rdyboost.sys because the ReadyBoost tab is absent from a USB drive’s properties. That is a different symptom from a boot error or a “file not found” message.
Microsoft-hosted guidance explains that Windows may hide ReadyBoost on systems with SSD storage because SSD access is faster than USB caching; Windows uses the SSD instead. On such a PC, the missing tab can be normal and does not prove that the driver file is broken.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11ReadyBoost is mainly relevant to older computers that use hard-disk storage and have limited memory. If the computer has an SSD and otherwise works, concentrate on ordinary performance checks: available storage, drive health, memory capacity, and page-file configuration. Do not force ReadyBoost by downloading a driver file or editing the system simply to restore a tab that Windows has intentionally omitted.
Windows 10 support and version context
Microsoft states that free Windows 10 support ended on October 14, 2025. Windows 10 continues to run after that date, but Microsoft recommends moving to Windows 11. Before assuming that a future Windows Update will fix rdyboost.sys, identify whether the machine is running Windows 10 or Windows 11 and note its edition and build. The exact build matters when selecting installation media as a DISM source.
For Windows 11, use media and update packages intended for the installed release. For Windows 10, the same DISM and SFC principles apply, but the end-of-support date means that update availability and assistance differ from a supported Windows 11 installation.
Quick Recap
Common mistakes to avoid
- Downloading a mirror copy: a SYS file from an unrelated site may be tampered with or incompatible. Repair the Windows image instead.
- Copying from another PC: even two computers that both say Windows 11 can have different builds, editions, languages, and update levels.
- Running only SFC: DISM repairs the component store that SFC may need, so run DISM first when Windows can start.
- Using C: automatically in WinRE: recovery environments often assign different letters. Confirm the volume containing the Windows directory.
- Using unmatched installation media: a different edition or build can leave DISM without the correct source.
- Interpreting a missing ReadyBoost tab as proof of failure: SSD-equipped systems may hide the feature normally.
- Ignoring repeated corruption: if repairs do not hold, include disk checking in the recovery plan rather than repeatedly replacing files.
Final verification checklist
- The computer now starts without a rdyboost.sys error.
- Online repairs were performed in the order DISM, SFC, restart, and Windows Update.
- Offline repairs used the volume letter that actually contains the Windows directory.
- Any DISM repair source matches the installed edition and build.
- A missing ReadyBoost tab was evaluated in the context of SSD storage instead of treated as proof of corruption.
- No SYS file was downloaded from an untrusted mirror or copied from an unrelated computer.
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