Although my article on ReadyBoost doesn't dwell on it, the Windows Vista feature that creates a code-page cache on a flash drive or flash memory card does put potential users of the feature in a bind, and reader Rich Farkas called me on it almost as soon as the article appeared. How, he wants to know, are potential Vista users supposed to know whether their PC will benefit from ReadyBoost? And once they figure that out, how are they supposed to know if ReadyBoost will work with their flash drive?If you've got Vista installed and you've got a flash drive you want to use for ReadyBoost, you've got no problems. Stick the flash drive in your PC and Vista will almost instantly let you know if it's nimble enough to work as a ReadyBoost cache.

But Rich and, I suspect, other people as well have a different problem. How can they know before they buy a flash drive that it will work with ReadyBoost? And even before they reach that point, how can they know that their PC, when equipped with a ReadyBoost-compatible flash drive, will perform well enough with Vista to make the upgrade process worthwhile?

"The thing about ReadyBoost that was not clearly identified by your article," Rich wrote, "is just how difficult it is to ascertain whether a flash drive will work or not. You mentioned the blogs and listings available out on the Internet, but in visiting these sites myself, I found the statements made about the usability of different manufacturer's flash types are conflicting to say the least and more often than not contradictory. I suspect there are system dependencies above and beyond the speed of the flash devices themselves that will allow a particular type of device to work well on some systems and not at all on others."

He would like some help from Microsoft on the front end of the whole process: "People don't want to upgrade from XP and then find out that (a) their existing computer really is incapable of running Vista satisfactorily, and worse (b) the flash drive they have is too slow to work to improve the situation, and even worse yet (c) make random attempts at trying different flash devices to see if any of them meet the loose and perhaps machine-dependant requirements for cache performance."

He mentions an existing test, the Windows Vista Upgrade Advisor, available from Microsoft, which neither he nor I am fond of. It says you can run Vista with only 512 Mbytes of RAM -- perhaps, but it probably won't run very well. I suggested a test I think is better in a previous blog entry, Tests Predict Your Old PC's Future: Vista or Vanished?. ATI's Vista Readiness Advisor does a thorough job of inventorying your PC and assessing its potential as a Vista machine. But, of course, it doesn't say anything about ReadyBoost or flash drives.

Rich describes what he'd like to see: "I think what users and technicians want is a simple utility that runs on the target XP machine. It should be run before a user attempts an expensive and frustrating Vista upgrade so the hardware can all be pre-tested to see whether the combination of the CPU, the USB architecture and the flash drive will work and deliver acceptable ReadyBoost cache performance. Then if the flash device passes that test using the target system that Vista will be installed on, a user can decide whether to take the Vista plunge with this older machine and existing and now pre-qualified flash drive. This will still not guarantee whether the experience will be satisfactory, but it will at least tell a user whether his flash device will test as being usable after installing Vista."

That seems reasonable, and it would certainly give most PC owners far more information that they've got now about how well their current hardware will work with Vista. But I suspect there's a little bit of a paradox about ReadyBoost. The less system memory a PC has, the more likely it will benefit from a ReadyBoost cache in flash. But if a PC has only 512 Mbytes of system memory, it probably has other lacks that will make it a poor candidate to run Vista well. The graphics, for example, are likely to be marginal, which is one reason I'm so enthusiastic about the ATI test: it does a good job of assessing the target PC's graphics subsystem because, natch, ATI makes graphics card.

For me, the bottom line is that while ReadyBoost will likely accelerate application execution some, and speed up boot-ups noticeably, by itself it won't turn a marginal PC into a good Vista performer. As my article said, there's no substitute for system memory, and I'd recommend that if you're considering upgrading to Vista you should also upgrade your hardware to run Vista well -- and that means a couple of gigabytes of RAM, a 2-Gbyte processor, and a new graphics card with half a gigabyte of video memory. With that configuration, you don't need to worry much about which flash drives run ReadyBoost.