I'm not sure what you're talking about. The issue is the difference between the two USB flash drives, and both used the same Windows driver. No rotation or tracks... I mentioned the test with a physical disk to point out that the PC is capable of sustained transfer rates. Most likely, each set of bytes sent to the USB stick are acknowledged, and this is at a speed that is much less than the PC is ultimately capable of. Over time, these acknowledgements come slower and slower. I find this odd, and am also curious why they both transfer small bursts quickly, but deviate so much from each other (same driver et al for both) by the end. -Skip Vasile Surducan wrote: > A comparison test can be performed knowing all driver characteristics. > For instance the track to track delay, physical dimension and rotating > speed. You should use the same USB/IDE converter for both drivers . > So, I'll test first the drivers on the IDE and only after a full > characterisation I'll move those on external USB units. > > On 4/9/07, Dr Skip wrote: > >> I just finished some informal testing of several jump drives, and it >> raised some questions. Perhaps someone here can explain this... >> >> I tested 2 drives on opposite ends of the advertised speed spectrum - >> one said 30MB/s read, 20 MB/s write (assuming the PC can do that) and >> was expensive, and the other was a 2 GB unit store brand for $15. No >> speed rating and the absolute cheapest I could find. Available by the >> handful in a barrel! Both were mounted in the same port on the same PC, >> with write caching turned off. >> >> With a read/seek/write test utility, they both showed 8.5MB/s writes for >> 5MB worth of data. This may be a limitation of the speed of the host PC, >> but not bad. >> >> An extended, 2GB write, slowed to 1MB/s on the first drive near the end, >> while the cheap one dropped to 200kB/s toward the end. The fast one took >> about 15-20 minutes to fill, the second took almost 2 hours. The first >> is reasonable to use real time, the second isn't. >> >> Considering there is no physical seek time, what would cause the speeds >> to drop so much over the full transfer? Why can't the speed be maintained? >> >> BTW, in comparison with a real hard drive, the port itself doesn't seem >> to slow down and the real drive maintains transfer rate, so that should >> rule out any PC buffering problem, at least to this big of a degree. >> >> Any ideas? >> >> -Skip >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist