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For the Raspberry Pi 1 I found some documentation (which I now can't find!) stating that the Ethernet NIC was connected via a USB bus so despite being a "100Mbps" NIC it had a max potential throughput of like 30Mbps (USB 2 bus I assume?), weather the CPU could push that much or not is a separate question.

Can anyone confirm (preferably by way of links to official documentation or schematics) what the "potential" throughput of the different Rasp Pi models is? I'm particularly interested in the model 2B and new model 3.

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    USB2 is 480Mb/s, so it's not the USB bus that limits the speed. – John La Rooy Mar 1 '16 at 0:14
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    Also worth noting that many modern devices don't seem to use all of the USB bus speed - currently quite a lot of USB 3 devices run below the max spec of USB 2.... – Wilf Mar 1 '16 at 8:01
  • @JohnLaRooy - Yeah sorry I meant USB 1 in that original post - even though that isn't the speed of USB 1 as it was an off-the-top-of-my-head figure, its not far out compared to mistakenly thinging USB2 can only push 30Mbps ;) – jwbensley Mar 7 '16 at 21:41
  • @Wilf - Yes this is very true - For the RaspPi2 I had heard that you will won't get near the 100Mbps limit of the NIC (again assuming the CPU was fast enough) because all the USB ports are sharing the same bus as the NIC port, even though the USB port's might even have nothing connected, the NIC only gets a faction of the BUS potential. But in both case these were hear-say and I'd like some real data/info. – jwbensley Mar 7 '16 at 21:44
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https://www.raspberrypi.org/documentation/hardware/raspberrypi/usb/README.md

To summarize:

  1. The total throughput of all the connected devices cannot be more than 480Mbps. Recall that the Ethernet port also goes through the USB.
  2. Don't try to pull more than 100mA from each port.
3

The highest I've seen the ethernet run at consistently, either personally or by people reporting numbers here, is in the range of 6-9 MB/s -- even the bottom end of that is quite a bit more than 30 Mpbs.

So no, there is no such limitation. Worth noting that it will do that while writing out through USB as well, which makes sense because the realistic data transfer speed of a USB 2.0 bus is probably 250-300 Mbps, and if the ethernet is using say 70, then writing back out at the same rate = 140 total, which yes it is capable of and will do about that in practice.

The take away, I think, is that it is not fast I/O wise by today's PC standards, but it is also atrociously slow in general by today's PC standards. It does not even stack up to most high quality modern smartphones, and it uses more power due to some lower quality components. However, it retails for $35-40 USD. The people who've made it have clearly stated their number one priority was low cost, not performance, and not low energy consumption. The reason for that is they wanted something that was easily affordable globally (as in, including the third world) for, e.g., educational institutions.

It's cheap. It's been very successful because it also (at least by now) pretty reliable, and has reasonable performance characteristics. You can run a crude desktop even on the single core models -- albeit perhaps frustrating compared to, say, your $500 laptop.

It is not:

  • A replacement for a production server.
  • A replacement for a desktop workstation.
  • A replacement for a normal, multicore, high power computer under any conditions.

I think a lot of people are hypnotized by the low price tag and some of the things some people with a lot of savvy and expertise have gotten it to do. I think a lot of those same people have been sadly disappointed when they get it and realize what <$50 worth of parts really adds up to. You get what you pay for. It is not a miracle device from a more technologically advanced alien species. It is a clever little thing from the UK.

One thing that is unusual about it and attracts a lot of people, vs. a PC or phone, is the GPIO breakout. While adding comparable bits to a normal computer may (or in fact, may not) be possible, it is going to cost you a lot more that a Pi just for the adapters (and put much more valuable equipment at risk of damage).

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    Thanks for the info although I'm not sure about the rant on what the RaspPi is or is not and what great value it is?! – jwbensley Mar 7 '16 at 21:47

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