Thanks to Mr. John Baker for the following information on Readyboost. 

You can see his blog at http://blogs.technet.com/johnbaker  

Windows Vista ReadyBoost Requirements

 

Supported Form Factors and Busses

ReadyBoost supports USB flash drives, Secure Digital cards, CompactFlash cards, Memory Stick over PCI, and PCIe and SSA busses, which effectively includes most internal card readers in mobile PCs. ReadyBoost does not support cards attached to external USB readers or devices attached to a USB 1.0 and USB 1.1 bus.

In general, any flash storage device that exposes a volume to Windows and meets minimum performance limits will be supported by ReadyBoost.

The following are requirements for USB flash devices enhanced for ReadyBoost:·

  • USB flash drives themselves and the host controllers they are inserted into must both use the USB 2.0 standard.
  • USB flash drives must have at least 230 MB of free space

Flash Performance

 

 

Flash storage devices must meet minimum performance requirements to support ReadyBoost, including 2.5 MB/s throughput for random 4K reads and 1.75 MB/s for random 512‑K writes.

Higher performance requirements must be met for the device to be designated as “enhanced for ReadyBoost”: 5 MB/s for random 4K reads and 3 MB/s for randmon 512‑K writes. Microsoft recommends that users use devices enhanced for ReadyBoost to take full advantage of the benefits provided by ReadyBoost.

Flash Capacity

ReadyBoost can support devices with cache sizes ranging from 230 MB to 4 GB. Microsoft recommends at least a 1:1 ratio of ReadyBoost cache size to main memory (RAM) capacity. Higher ratios up to 3:1 will realize the optimal performance benefits.

 

Flash Wear

Some types of NVRAM (such as NAND) are rated for a limited number of write-erase cycles before individual cell failure occur. To limit the possibility of cell failure, ReadyBoost has been designed to carefully manage when it writes to the cache. Initial testing of devices enhanced for ReadyBoost indicates that users can expect many years of use under typical workloads. The absolute lifetime of each device will vary depending on device capacity and manufacturer.