ReadyBoost - Using Your USB 2.0 Flash Drive to Speed Up Windows Vista
One very cool feature of Windows Vista – especially for machines not natively equipped with the kind of horsepower to fully enjoy the rich visuals of Windows Presentation Foundation (Avalon) applications is ReadyBoost. ReadyBoost enables you to plug a USB key into your machine and have Windows Vista use it as memory.

Installing/Configuring the USB 2.0 Flash Drive as Memory
First I took a standard USB 2.0 key (I’ll list the prerequisites shortly) and plugged it into my machine. Upon plugging the USB key into my computer, I was greeted with the standard "AutoPlay" dialog box asking how I wanted to the operating system to treat the USB key. However, with ReadyBoost I get the additional option (circled below in the screen capture) of using the key to "speed up my system".

Once I click the "Speed up my system" option, the Properties dialog box for the device is displayed where I can specify to start/stop ReadyBoost usage of the device and how much space I want used as a memory cache. (Actually, according to one of the Product Specialists here, this space is used more as a flash-based page file than true RAM, but the impact is that the more space you choose here, the more benefit you’ll get in terms of overall system performance.)

(In order to return to this dialog box, open the Computer window, right-click the drive (F: in this case) and select Properties. From there, click the Memory tab (as shown in the previous screen capture and adjust the settings as needed).

For the inquisitive, opening the drive in an Explorer window reveals that ReadyBoost has created a cache file of the specified size.

Things to Know About ReadyBoost
If you have a USB key configured to use ReadyBoost and then insert a second key, Windows Vista will display the Properties dialog box where you’ll see the message on the Memory tab as shown in the following screen capture.

While ReadyBoost will work with other devices – such as SD Card, CompactFlash, etc. – I’ve only used it with a USB key and here are the baseline requirements the team gave me regarding what ReadyBoost will work with:

The capacity of the removable media must be at least 256 MB
Devices larger than 4GB will have only 4GB used for ReadyBoost
The device should have an access time of 1ms 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
The device must have at least 235 MB of free space
NTFS and FAT32 are supported
The initial release of ReadyBoost supports only ONE device

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Q&A From Microsoft:

Q: Why can't I use more than 4GB of flash?
A: The FAT32 filesystem limits our ReadyBoost.sfcache file to 4GB

Q: Aren't Hard Disks faster than flash? My HDD has 80MB/sec throughput.
A: Hard drives are great for large sequential I/O. For those situations, ReadyBoost gets out of the way. We concentrate on improving the performance of small, random I/Os, like paging to and from disk

Q: What happens when you remove the drive?
A: When a surprise remove event occurs and we can't find the drive, we fall back to disk. Again, all pages on the device are backed by a page on disk. No exceptions. This isn't a separate page file store, but rather a cache to speed up access to frequently used data.

Q: Why don't you support SD on my USB2.0 external card reader?
A: We unfortunately don't support external card readers - there were some technical hurdles that we didn't have time to address. In general, if a card reader shows a drive without media in it (like a floppy drive or CD ROM does), we can't use it for ReadyBoost.

Q: Can you use an mp3 player to speed up your system?
A: Not currently. MP3 players use the 'plays for sure' interfaces to expose themselves to Windows. We require that the device appear as a disk volume. These aren't currently compatible.

Q: How much of a speed increase are we talking about?
A: Well, that depends. On average, a RANDOM 4K read from flash is about 10x faster than from HDD. Now, how does that translate to end-user perf? Under memory pressure and heavy disk activity, the system is much more responsive; on a 4GB machine with few applications running, the ReadyBoost effect is much less noticable.

Q: I can't get my device to work with ReadyBoost... can I lower the perf requirements?
A: Unfortunately, no. We've set the perf requirements to the lowest possible throughput that still makes your system faster. If we lowered the perf requirements, then there wouldn't be a noticeable benefit to using ReadyBoost. Remember, we're not adding memory, we're improving disk access.

Q: Which manufacturers support ReadyBoost?
A: Well, I hope that all of them do, eventually. Right now, we're working with manufacturers to create a program that will allow them to identify ReadyBoost capable devices on their packaging. Flash Drives from Netac Technology are compatible with ReadyBoost.