Usually, tuning up a PC requires a lot of work, spending much money on new components, or both. ReadyBoost can speed up slow or overwhelmed PCs without either one.

There’s no such thing as a fast-enough computer. No matter how hot your CPU runs or how much RAM you have, eventually you’ll run out of performance — usually, just when you need it most. Fortunately, Windows 7 comes with a cheap and easy way of improving system performance: ReadyBoost.

Windows 7’s ReadyBoost is Microsoft’s latest take on a very old idea for improving computer performance: caching. With a cache, you gain speed by keeping frequently accessed data as close as possible to the CPU cores. The faster the cache, the closer it should be to cores. That’s why high-end processors, like the Intel i7 quad-core CPU, have their own on-board cache.

Caching used to be easy. You used caching on uniprocessor, single user systems to free yourself from the slow I/O jail, whether that I/O was from the system bus to the processor or from the hard drive to the bus. As multiple-CPU and core systems became more common, simply placing fast RAM between system components with varying I/O throughputs was no longer enough. System designers had to contend with making sure that the available data to the processor was the real, newest data.

In ReadyBoost, cached data is stored in a Flash memory drive (usually a USB stick, but Secure Digital (SD) and Compact Flash (CF) cards are also supported). When data is read at random rather than in large blocks of data, ReadyBoost can improve file and data read input/output (I/O) by several times over traditional hard drives. You also get a performance boost from random writes, but it won’t be as significant.

In Windows 7, caching is usually done with SuperFetch and ReadyBoost working hand in glove. That’s setting aside such specialized caches as DNS cache (for Domain Name Service Internet addressing), Thumbnails cache (which contains downloaded ActiveX and JavaScript programs), and network file caching programs (such as BranchCache).

SuperFetch watches for which applications, documents, and system programs you use the most often and pre-loads them into your system memory. This way they’re ready to spring into action when you call on them. Of course, you could be using that RAM for other, potentially more useful work like running memory-hungry programs such as Adobe Photoshop or InDesign. In short, if you have relatively little RAM, or you’re using most of it, you should see some benefits from using ReadyBoost.

The other situation where you’ll see some performance improvements from ReadyBoost is when the computer has a slow hard disk drive. Computers with a hard disk Windows Experience Index (WEI) sub-score lower than 4.0 should see the most significant improvements. Conversely, if you have a very fast hard drive, such as a solid state drive (SSD), you won’t see any benefit from a USB 2.0 drive. Indeed, by default, Windows 7 disables ReadyBoost if you’re using an SSD drive.

Unfortunately, not all SD and CF cards, or even USB flash drives, work with ReadyBoost. While some storage media advertise that they’re “enhanced for Windows ReadyBoost,” they may not actually be ReadyBoost worthy. For a device to be ReadyBoost capable, it has to be able to handle 2.5 MBps throughout for 4 KB random reads and 1.75 MBps throughout for 512 KB random writes. In addition, the device must have at least 235 MB of available storage.

To my surprise, I’ve found that some ancient, tiny USB drives were ReadyBoost ready while other, brand-new drives failed. If you’d rather not waste time buying and trying USB drives, there’s a useful ReadyBoost Compatibility List based on real-world testing.

When you first attach a flash drive that ready for ReadyBoost, AutoPlay should provide ReadyBoost as an option. Even if you don’t see that as an option, you may still be in luck.