07-12-2012, 01:01 PM
Windows 7 has a feature called "ReadyBoost" (first introduced in Vista) that allows you to use a USB memory stick or an SD card as a disk cache. It's especially useful on machines with 2GB or less RAM, but widely regarded to be of little benefit if you have lots of RAM. In Vista, you were limited to a single 4GB cache file, but on Windows 7 you can have up to 8 32GB files on up to 8 devices (one file per device). I just maxed out my laptop at 8GB RAM, but I use a *lot* of memory. With 4GB my total committed VM was typically around 7.5GB and my machine spent a lot of time paging. My machine has an SD card slot that I never use, so I'm considering getting an SD card to put in there exclusively for ReadyBoost. It might not help a ton, but it can't see how it could hurt so I'm inclined to give it a try.
But ReadyBoost has a 'random' access pattern, reading and writing small blocks all over the flash drive. Modern flash drives are optimized for 'sequential' access, so that large files can be read or written quickly, but random access suffers as a result. This is particularly true for SD cards which are optimized for the needs of digital cameras and camcorders (fast sequential reads and writes). This means that you can't look at a flash drive's speed rating to get a clear idea of whether it will work well with ReadyBoost or not. a "C10" rated SD card might work horribly with ReadyBoost compared to a theoretically-slower "C6" rated card.
So, does anybody have any idea which SD cards have good random access times? I'm looking for a 32GB SDHC card (I don't think my SD card reader will recognize SDXC or UHC-1 cards). I've identified an HP 32GB SDHC card as a possible option. From what I saw on Kingston's web site, they refuse to certify any of their SD cards for use with ReadyBoost. SanDisk may have some options but good data is hard to get.
-ken
But ReadyBoost has a 'random' access pattern, reading and writing small blocks all over the flash drive. Modern flash drives are optimized for 'sequential' access, so that large files can be read or written quickly, but random access suffers as a result. This is particularly true for SD cards which are optimized for the needs of digital cameras and camcorders (fast sequential reads and writes). This means that you can't look at a flash drive's speed rating to get a clear idea of whether it will work well with ReadyBoost or not. a "C10" rated SD card might work horribly with ReadyBoost compared to a theoretically-slower "C6" rated card.
So, does anybody have any idea which SD cards have good random access times? I'm looking for a 32GB SDHC card (I don't think my SD card reader will recognize SDXC or UHC-1 cards). I've identified an HP 32GB SDHC card as a possible option. From what I saw on Kingston's web site, they refuse to certify any of their SD cards for use with ReadyBoost. SanDisk may have some options but good data is hard to get.
-ken