ReadyBoost has been around since the days of Windows Vista. It is a little known Windows feature that can use external USB flash drives (or SD cards or CF cards), as a hard disk cache to speed up disk read performance. As we will explore in this article, there are times when ReadyBoost can be used as an effective tool as well as times when it shows no performance enhancement at all.

As a performance tool ReadyBoost is smart and well-designed. Instead of actually caching file writes, it acts as a write-through cache. This implementation means that data is still written to the hard drive and will not be lost if the USB drive is pulled out of the port. Also, all data uses AES-128 encryption so that if the USB drive is lost or stolen, the data will be protected.

ReadyBoost relies on the SuperFetch technology that was first implemented in Windows Visa. This technology analyses the computer behavior patterns and loads often used data components into memory before they are required to speed up performance.

ReadyBoost is aware that reading large sequential files from flash memory is actually slower than reading it from a fairly speedy hard drive, so it allows the system to read such large sequential data directly from the hard drive. The drive, assisted by on onboard data buffer, however is speedier than such a hard drive for smaller blocks non-sequential files, so ReadyBoost handles those.

The bottom line about the usability of ReadyBoost is that if you have a hard drive with really speedy read/write access, ReadyBoost will be of little use to you. If Windows is installed on an SSD, ReadyBoost will actually be disabled since the speed of the disk will surpass the speed of the external drive. However, computers with average or below-average read-write drives can see a significant increase in speed with ReadyBoost. This is true with all current versions of Windows including Windows 10.

Requirements of the external drive to be used with ReadyBoost are:

  • Capacity of at least 256 MB, with at least 64 kilobytes (KB) of free space. Windows will use up to 4 GB of space, but you can use a higher capacity drive and still employ the remaining space for other data.
  • At least a 2.5 MB/sec throughput for 4-KB random reads
  • At least a 1.75 MB/sec throughput for 1-MB random writes

ReadyBoost will use 4 GB of space on the drive and this doesn’t sound like much. However, ReadyBoost compresses and encrypts all the data that is put on the external device. Microsoft states that the compression that occurs has a typical ratio of 2:1 which means that a 4GB drive can contain approximately 8GB of data.

Obviously a USB3 drive will be speedier than an older USB drive. Not all USB drives, however, no matter what version they are, are created equal. Yet with ReadyBoost, if you have an external drive available, you don’t have to fret about its speed. Just insert your device into the computer, access its Properties dialog as select the ReadyBoost tab.

USB properties

If you don’t see the ReadyBoost tab, it means that the external drive will not support ReadyBoost. In most cases, however, you will see a ReadyBoost tab and a notice saying that ReadyBoost is assessing the capabilities of the drive. If the external drive is not up to the ReadyBoost standards you will be presented with a “failed” screen as shown below. Unfortunately, Windows will not tell you why the drive is not compatible with ReadyBoost, it simply gives you a “failed” screen.

failed readyboost

If the drive is acceptable, you will be presented with a screen that allows you to dedicate the entire device to ReadyBoost or to reserve a certain amount of space on the drive for ReadyBoost. To see an increase in performance you will want to reserve the maximum 4094 MB, which is the largest amount useable by the Windows operating system.

readyboost ok

If you are using a USB drive, are really focused on speeding up your system, and ReadyBoost only offers a small improvement, you might try reformatting the drive using the NTFS or exFat file system. Normally USB drives are formatted using the FAT32 file system. exFat is a newer file system for flash drives. For more information on this, check out this file performance comparison of the FAT32, NTFS, and exFAT systems when used on a USB3 Drive.

You can also try using more than one ReadyBoost device. Windows allows multiple caches, on per device, up to a total of 256 GB.


In summary, if the drive head has to move many times to access small chunks of data and your hard drive is not very speedy, ReadyBoost can improve performance. If you are streaming a video or performing a similar task, you won’t notice a difference. And if you have a very speedy hard disk, you probably won’t notice a difference. However, since ReadyBoost is built into Windows 7, Windows 8.1 and Windows 10, the only cost to trying it is an inexpensive 4GB portable drive. Especially for older and slower systems it may be the best way to speed up your computer without complicated technical modifications.



Sandy Berger, respected computer authority, journalist, media guest, speaker, and author, has more than three decades of experience as a computer and technology expert. Her eight books include: How to Have a Meaningful Relationship with Your Computer, Your Official Grown-up's Guide to AOL and the Internet, Cyber Savers –Tips & Tricks for Today’s Drowning Computer Users, Sandy Berger’s Great Age Guide to Better Living through Technology, Sandy Berger’s Great Age Guide to the Internet, Sandy Berger’s Great Age Guide to Gadgets & Gizmos, Sandy Berger’s Great Age Guide to Online Health & Wellness, and Sandy Berger’s Great Age Guide to Online Travel. Sandy’s newspaper column, magazine articles, feature stories, product reviews, and computer tips can be found at her website, Compu-KISS.