sascha wrote: > > SATA SSD seems to cost same as USB memory sticks. > > its about 30% more expensive
Ouch. I was looking at really expensive USB memory. > > USB is widely available, but still a serial bus, so only a single > > request to a single memory stick per host controller is in flight at > > any one time. (Even with 8 USB ports it's still one controller.) > > tests show otherwise: > single usb stick: > Results: 967 seeks/second, 1.03 ms random access time > > 3 usb sticks on a hub accessed concurrently: > Results: 907 seeks/second, 1.10 ms random access time > Results: 916 seeks/second, 1.09 ms random access time > Results: 915 seeks/second, 1.09 ms random access time On the wire there are 1ms timeslots (called frames) that can each be used for communication with different devices. I expect the seek to be near-nop in the device so this measures the minimum USB RTT. It gets worse when transfering data - how bad depends on burst size. What size are reads(?) between two seeks? USB has lots of layers and if the bursts are very small then overhead is expensive. Compare products like NANdrive, which might be inside that USB memory: http://sst.com/products/solid-state_storage.dot?cat=nd "Minimum PIO Transfer Cycle Time" 120ns. (32 bits of data) High-end CF should be on par with this, and functionally equivalent. But 12x24mm per 8GB is a much nicer size than CF form factor. Another view - what bandwidth is desireable if storage seeks can be neglected? //Peter _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
