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Vista's ReadyBoost can improve cache performance, but it's not for everyone

There are five stipulations you need to know about before you can take advantage of ReadyBoost, the Windows Vista feature that allows flash storage to be used for virtual memory.

There are so many new features in Windows Vista that some them may not be getting their due. One of the more striking advances in Vista is something I've heard discussed in a theoretical way before, but I didn't imagine Microsoft would actually go so far as to implement it: using flash drives as swap space.

Why has Microsoft never implemented this before? There are primarily two reasons:

  1. Flash drives are removable (there are really no flash versions of a fixed disk), which means that, at any time, the data on them might no longer be available.
  2. Flash drives aren't always as fast as they need to be to support such operations.

Microsoft took both of these conditions into account when they created ReadyBoost, the Vista feature that allows flash storage to be used for virtual memory. However, there are five stipulations regarding the use of ReadyBoost:

  1. ReadyBoost can only be used on a device that has a consistent 2.5 MB/sec 4K random read throughput and 1.75 MB/sec 512K random write throughput. When a new device is mounted and prepared for ReadyBoost, Windows conducts several speed tests on the device to ensure that it can be used. However, not all flash devices have consistent read/write throughput. Some have a block of fast memory and several blocks of slow memory, and for that reason can't be used for ReadyBoost.
  2. The largest amount of flash memory that can be used for ReadyBoost is 4GB, which is the largest file that can be created in the FAT32 filesystem. (From what I understand about Vista, it is possible to format a removable drive with NTFS—something not possible in XP—but still not recommended.)
  3. The brunt of the data handled by ReadyBoost is small random I/O operations, rather than large sequential reads (which is what hard drives are best for).
  4. All the data stored in a ReadyBoost cache is backed up by a pagefile on a hard disk. If the flash drive with the ReadyBoost cache is unplugged, Vista falls back to the hard drive so no data loss takes place.
  5. You can only use one flash device per computer.

In an organization whose policy prohibits the use of flash devices or external hard drives, it wouldn't be possible to take advantage of ReadyBoost. And, unless ReadyBoost were to show a truly significant increase in performance, it might not be worth bending or revising policy to allow flash drives for the sake of this feature. For systems with 512MB or less, it's probably possible to get the same results by simply upgrading to a machine with more physical memory. For Vista, that would probably be a good idea anyway.

About the author: Serdar Yegulalp is editor of the  Windows Power Users Newsletter, which is devoted to hints, tips, tricks, news and goodies for Windows NT, Windows 2000 and Windows XP users and administrators. He has more than 10 years of Windows experience under his belt, and contributes regularly to and

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