Ok, I was thinking to HDD on USB. On 4/10/07, Dr Skip wrote: > 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 > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist