ReadyBoost is a special disk cache service in Windows Vista, 7, 8 and 8.1 that uses fast removable devices, such as USB flash drives, Secure Digital and CompactFlash cards for speeding up smaller random disk reads. This can significantly improve Windows performance when many random small files are read frequently or when computer does not have sufficient amount of RAM (Random Access Memory). Traditional hard disks (not SSD-s) are often up to 80 times slower than removable devices in reading random small files. That's why you cannot use external hard disks for ReadyBoost - no real performance gain is possible.
A suitable USB port for ReadyBoost must support at least USB 2.0 standard, and USB 3 (SuperSpeed, blue ports) is even better.
In 32-bit versions of Windows Vista, 7 and 8/8.1, and on FAT32 file system devices, you can use up to 4 GB (gigabytes) of storage for ReadyBoost. Older FAT16 file system can also be used, but maximum cache size is limited to 2 gigabytes then.
In 64-bit Windows, up to 32 GB of cache can be created on a single NTFS-formatted removable drive, even if the drive itself is larger. Windows 7 and 8/8.1 also support exFAT file system (cache up to 32 GB in size, too) for ReadyBoost.
On FAT16 and FAT32 drives, file size limits of 2 and 4 gigabytes still apply.
You can convert FAT/FAT32 drives to NTFS file system without losing any data if you want to use ReadyBoost cache larger than 2 or 4 gigabytes. Read the Disk Management in Windows article for detailed instructions.
While Windows Vista supports only one ReadyBoost drive at a time, Windows 7 and later allow combining up to 8 different removable devices. Therefore, in 64-bit Windows you can create ReadyBoost cache of up to 8 x 32 GB, or 256 GB in total size.
You need a USB stick or memory card that has at least 250 megabytes of disk space (one to three times the amount of RAM is recommended), access time under 1 millisecond, random read speed at least 2.5 megabytes/second and random write speed at least 1.75 megabytes/second.
Windows Vista, 7, 8 and 8.1 always check the speed of removable devices automatically, so you do not need to run these tests yourself.
If Windows is installed on a SSD (Solid State Disk), ReadyBoost will automatically be disabled because no performance gain can be achieved.
ReadyBoost cache file is always encrypted using AES-128 algorithm to prevent data leakage. Compression is also used to cram up to two times more data into the file.
Please note that adding more RAM to a computer always enhances performance even more. But if you use 32-bit Windows and your computer already has 4 GB of RAM installed (the maximum supported), ReadyBoost can be helpful in speeding up application launches.
In a test cited on Wikipedia, the time to complete a specific operation was decreased from 11 seconds to 2 seconds using ReadyBoost on Windows Vista PC with 512 megabytes of RAM. But doubling the amount of memory and turning off ReadyBoost decreased the time to 0.8 seconds.
Please do not expect ReadyBoost to turn an ages-old Celeron computer into a brand new eight-core i7 though. ReadyBoost does not speed up processors or RAM, it enhances hard disk access times for small random reads - the effect is most noticeable while launching larger disk-intensive programs such as Adobe Photoshop, Microsoft Outlook, etc.
Also, check Windows Experience Index (WEI) subscore for primary hard disk - if the score is low, ReadyBoost's positive effect will be more noticeable. In case your hard disk is rated at or near maximum (5.9 in Windows Vista; 7.9 in Windows 7; 9.9 in Windows 8), there might be no point in using ReadyBoost. Please note that WEI is not available in Windows 8.1.
You should always dedicate the whole removable drive to ReadyBoost because forcibly removing it while Windows is working can result in multiple errors (files not found, programs crashing, etc). You should always use the Safely Remove Hardware icon to remove ReadyBoost drives properly.
Always use a USB drive or memory card with capacity that at least equals the amount of main memory (RAM) installed in your PC. So if you have 2 GB of RAM, you should choose a drive with 2 or more gigabytes of disk space. This ensures that ReadyBoost performs optimally.
You can check the total amount of RAM in your computer using keyboard shortcut Windows Key+Pause/Break. Alternatively, right-click (My) Computer / This PC icon on Desktop or in Start menu and select Properties.
For larger (over 4 GB) drives, it is strongly recommended to convert the existing FAT/FAT32 file system to NTFS. This can be done without any data loss and it enables creating ReadyBoost cache larger than 2 (FAT/FAT16) and 4 (FAT32) gigabytes.
First, connect the drive you want to use for ReadyBoost. If AutoPlay/AutoRun is enabled, you can click the Speed up my system using Windows ReadyBoost option.
Please note that this option is available even if the drive does not meet minimum requirements for ReadyBoost!
Alternatively, you can open Windows/File Explorer (keyboard shortcut is Windows key+E), right-click the removable drive and select Properties from the menu.
Open the ReadyBoost tab.
If Windows states that "This device cannot be used for ReadyBoost - The device does not have the required performance characteristics for use in speeding up your system", you should try another, faster drive.
Although there are many articles online that show how to tweak Windows Registry to allow ReadyBoost on slow drives, I strongly suggest against doing so - using a sluggish removable drive can slow down Windows even more.
If ReadyBoost options appear, you can use the device for speeding up Windows Vista, 7, 8 and 8.1.
In Windows Vista, enable the Use this device option and move the Space to reserve for system speed slider all the way to the right.
In Windows 7, 8 and 8.1, select the Dedicate this device to ReadyBoost option.
The Windows recommends reserving <number> MB for optimal performance field always reserves some space for file storage, so it is largely irrelevant.
Click OK to create ReadyBoost cache on the disk.
Windows then creates a special encrypted and compressed file named ReadyBoost.sfcache on the disk.
It takes some time for the cache to fill with data - files related to Windows are added first, followed by open applications and programs you launch. This causes temporary bump in disk activity. Allow ReadyBoost to do its work for at least two or three days and see if applications start and run faster. Generally, Windows and installed programs should be more responsive if ReadyBoost has enough disk space for its cache.
To turn off ReadyBoost, open the Removable Disk Properties again and select the Do not use this device option.