On 2015-10-13 21:20, Xen wrote:
"Carlos E. R." <> schreef:
Depends on what controller you have. There is a cheaper one that is as you say, and another, more expensive one, which is autonomous.
I only know traditionally the USB2 controller was the biggest determinant of how fast a usb device would be. I guess that would still be the case today.
Well, for USB2 on reasonably powerful computers, USB can handle near the rated maximum speed, which is 480 Mbit/s (https://en.wikipedia.org/wiki/USB#Transmission_rates). Assuming the CPU load is not too big and that there are no more devices plugged to the same bus. From the wikipedia: +++-------------- The theoretical maximum data rate in USB 2.0 is 480 Mbit/s (60 MB/s) per controller and is shared amongst all attached devices. Some chipset manufacturers overcome this bottleneck by providing multiple USB 2.0 controllers within the southbridge. According to routine testing performed by CNet, write operations to typical Hi-Speed (USB 2.0) hard drives can sustain rates of 25–30 MB/s, while read operations are at 30–42 MB/s;[128] this is 70% of the total available bus bandwidth. For USB 3.0, typical write speed is 70–90 MB/s, while read speed is 90–110 MB/s.[128] Mask Tests, also known as Eye Diagram Tests, are used to determine the quality of a signal in the time domain. They are defined in the referenced document as part of the electrical test description for the high-speed (HS) mode at 480 Mbit/s.[129] According to a USB-IF chairman, "at least 10 to 15 percent of the stated peak 60 MB/s (480 Mbit/s) of Hi-Speed USB goes to overhead—the communication protocol between the card and the peripheral. Overhead is a component of all connectivity standards".[130] Tables illustrating the transfer limits are shown in Chapter 5 of the USB spec. For isochronous devices like audio streams, the bandwidth is constant, and reserved exclusively for a given device. The bus bandwidth therefore only has an effect on the number of channels that can be sent at a time, not the "speed" or latency of the transmission. --------------++- -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar)