Windows Vista Ready Boost

ReadyBoost is a component of Microsoft's Windows Vista operating system. It works by using flash memory, USB 2.0 drive, SD card, CompactFlash or any kind of portable flash mass storage system as a drive for disk cache.

ReadyBoost is present, with fewer restrictions than in Vista, in the beta version of Windows 7.ReadyBoost is also used to facilitate SuperFetch, an updated version of Windows XP's prefetcher which performs analysis of boot-time disk usage patterns and creates a cache which is used in subsequent system boots.

Using ReadyBoost-capable flash memory (NAND memory devices) for caching allows Windows Vista to service random disk reads with performance that is typically 80-100 times faster than random reads from traditional hard drives. This caching is applied to all disk content, not just the page file or system DLLs.

Flash devices are typically slower than the hard drive for sequential I/O, so to maximize performance, ReadyBoost includes logic to recognize large, sequential read requests and then allows these requests to be serviced by the hard drive.
When a compatible device is plugged in, the Windows AutoPlay dialog offers an additional option to use the flash drive to speed up the system; an additional "ReadyBoost" tab is added to the drive's properties dialog where the amount of space to be used can be configured.

250 MB to 4 GB of flash memory can be assigned. ReadyBoost encrypts, with AES-128, and compresses all data that is placed on the flash device; Microsoft has stated that a 2:1 compression ratio is typical, so that a 4 GB cache could contain upwards of 8 GB of data.

According to Jim Allchin, for future releases of Windows, ReadyBoost will be able to use spare RAM on other networked Windows Vista PCs.For a device to be compatible and useful it must conform to the following requirements:
• The capacity of the removable media must be at least 256 MB (250 after formatting)
• Devices larger than 4 GB will have only 4 GB used for ReadyBoost
• The device should have an access time of 1 ms or less
• The device must be capable of 2.5 MB/s read speeds for 4 KB random reads spread uniformly across the entire device and 1.75 MB/s write speeds for 512 KB random writes spread uniformly across the device
• NTFS, FAT16 and FAT32 are supported (Windows 7 and Vista SP2 will support also the new exFAT filesystem)
• The initial release of ReadyBoost for Windows Vista supports one device. Windows 7 supports the simultaneous use of ReadyBoost on multiple flash drives.
• The recommended amount of flash memory to use for Windows ReadyBoost acceleration is one to three times the amount of random access memory (RAM) installed in your computer depending on the brand, wear and tear due to read-write cycles, and size of the flash memory, the ability to format as NTFS may not be available. Enabling write caching on the flash drive by selecting Optimize for performance in Device Manager will allow formatting as NTFS.

source:wikipedia