I recommend reading:
http://www.steves-digicams.com/flash_memory.html
and
http://www.tomshardware.com/reviews/data-transfer-run,1037.html
I've found that it's often hard to determine how "fast" a flash drive (or flash memory) is. Often the manufacturer won’t easily give that kind of information out, almost always because it's a slow performer.
There seem to be three ways the speed of flash memory is rated. One is "class". A Class 2 flash drive should have a transfer rate of around 2 megabytes per second. Class 4 would be 4 MB/sec. Class 6 - 6 MB/sec.
Another way speed is described is similar to how optical drives specify speed - using ###x such as 50x, 100x, 133x, 233x, 300x, etc... To get the MB/sec speed you multiply the number by 150 kilobytes per second. So, 100x would be 15,000 KB/sec or about 14.65 MB/sec. 133x = 19.48 MB/sec, 233x = 34.13 MB/sec, 300x = 43.95 MB/sec.
And still, sometimes the drive either has no designation of speed, uses MB/sec or Mbps/MBps. MBps means Mega
bits per second, to convert that to mega
bytes per second, you divide by 8. For some reason (consumer confusion no doubt) manufacturers have adopted the meaning for 1 megabit to equal 1,000,000 bits, instead of 1024*1024 = 1,048,576 bits (how hard drives report capacity). So, 10 MBps = 10,000,000 bits per second / 8 = 1,250,000 bytes per second = 1.192 MB/sec. 24 MBps = 2.86 MB/sec.
Another thing to keep in mind is the speed of the USB drive. Most USB ports are version 2.0 and can operate at a theoretical 60 MB/sec. Older specifications are 1.5 MB/sec or less. A new specification USB 3.0 is shown on wikipedia as being capable of 625 MB/sec, although I doubt we'll see devices that can take advantage of that much throughput in the next few years.
I feel that there are two basic ways to go about flash memory. Get one of those rather slow USB flash drives which are convenient, or one of the plethora of other flash memory media used by digital cameras and other electronic devices. Most decent photo printers come with flash card readers (although the transfer speed may be dubious), or you can buy a flash card reader for less than $20 (Transcend seem to make popular models). Of course you’ll have to take into consideration that the reader might be a speed bottle-neck.
With a flash card reader, which you can find a fairly small one, and most connect to the USB port. Though, it might need special drivers. I don’t know for sure, but I suspect XP/Vista will recognize them without special drivers. Compact flash (CF) memory is much faster than most of the even faster USB flash drives, and are often rated from 133x (19MB/s) up to 300x (42.91MB/s). Which compared to the paltry speed of a class 6 USB flash drive (6 MB/sec) is leaps and bounds better, keep in mind that you have to have a card reader for CF memory. I suspect that due to the dimensions of CF memory, unless it can be made smaller and more compact (which might sound funny considering the C in CF stands for compact – CCF anyone?) we probably won’t see CF flash memory used in USB flash drives anytime soon. However, SDHC memory is small, and getting faster. SanDisk extreme III SDHC shows a transfer speed of 20 MB/sec, and prices are coming down.
What seems to be a type of flash memory which was introduced not too long ago (2005), and looks like it might become obsolete mostly because of the success and wide adoption of SD flash memory, and CF flash memory - is MMC(plus) flash memory (stands for MultiMedia Card) which is faster than SD memory and cheaper than CF memory; rated to transfer at around 50 MB/sec. You can buy a Transcend 4GB MMCplus card for $10 right now at newegg. It might be cheap because it’s reaching its end-of-life.
I guess it’s another one of those “too-good” things that get axed by the big executives.