Windows‌ ReadyBoost can use storage space on some removable media devices, such as USB flash drives, to speed up your computer. When you insert a device with this capability, the AutoPlay dialog will offer you the option to speed up your system using Windows‌ ReadyBoost . If you select this option, you can then choose how much memory to use for this purpose. However, there are some situations where you may not be able to use all of the memory on your storage device to speed up your computer.

Some universal serial bus (USB) storage devices contain both slow and fast flash memory, and Windows can only use fast flash memory to speed up your computer. So if your device contains both slow and fast memory, keep in mind that you can only use the fast memory portion for this purpose.

The recommended amount of memory to use for Windows‌ ReadyBoost acceleration is one to three times the amount of random access memory (RAM) installed in your computer. For instance, if your computer has 512 megabytes (MB) of RAM and you plug in a 4 gigabyte (GB) USB flash drive, setting aside from 512 MB to 1.5 GB of that drive will offer the best performance boost. The minimum size for any USB flash drive to work with Windows‌ ReadyBoost is 256 MB.

You can enable or disable Windows‌ ReadyBoost for a specific flash drive or other removable storage device. For more information, see Turn ReadyBoost on or off for a storage device.

What to look for

Here are some tips about what to look for when purchasing a USB flash drive you plan to use with Windows‌ ReadyBoost :

  • Make sure there is at least one free USB 2.0 port on your computer where you can plug in the flash drive (preferably not on an external USB hub shared with other USB devices).

  • Look for a note from the manufacturer that the flash drive is Windows‌ ReadyBoost Compatible. Not all manufacturers list this on their packaging.

  • If the flash drive is not labeled as compatible with Windows‌ ReadyBoost , check its specifications to see if it is capable of reading and writing data fast enough. The speed requirements for Windows‌ ReadyBoost are at least 2.5 MB per second throughput for 4 kilobyte (KB) random reads and 1.75 MB per second throughput for 512 KB random writes.


  • A flash drive may appear to meet these requirements, but Windows Vista still may not detect the device as ReadyBoost -compatible if its rated speed measures sequential performance instead of random performance, and if performance is not consistently fast across the entire flash drive.