ReadyBoost lets you use an SD card or USB drive to “add” RAM to Windows 7. In order to use ReadyBoost, you have to have the sysmain service, also called Superfetch, enabled.
If you try and enable ReadyBoost and see “This device cannot be used for ReadyBoost. ReadyBoost is not enabled because the service responsible for ReadyBoost (Sysmain) has been turned off on this computer. etc, etc” you simply need to turn it on.
Start > Run > cmd > and type net start sysmain
Make sure you are running this as administrator so you don’t get an Error 5 Access Denied message.
If you receive a “System error 1058 has occured,” more than likely the sysmain service has been disabled.
To enable it, click on Start and type in services.
Right-click the Services item with the cog/gear icon next to it and run as administrator.
Scroll down to Superfetch. Right-click > properties > Startup type: Automatic > Apply > OK
Go back to the command prompt and type net start sysmain. The service should start successfully.
ReadyBoost is now usable again.