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Date:      Sun, 22 Jul 2012 20:20:06 -0500
From:      Adam Vande More <amvandemore@gmail.com>
To:        Jakub Lach <jakub_lach@mailplus.pl>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: "da0: 40.000MB/s transfers" What was rationale behind pegging USB 2.0 at 40MB/s?
Message-ID:  <CA+tpaK22qemQgGLJCy0R9X8poL8W1kcNGyw_ZgH9n9-a8JZmfg@mail.gmail.com>
In-Reply-To: <1342998350089-5729042.post@n5.nabble.com>
References:  <1342992043358-5729028.post@n5.nabble.com> <CA+tpaK3qWnh_MUfBAEzTexsJdXu4JP5nPG=z4jJdUUd2qwSUxQ@mail.gmail.com> <1342998350089-5729042.post@n5.nabble.com>

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On Sun, Jul 22, 2012 at 6:05 PM, Jakub Lach <jakub_lach@mailplus.pl> wrote:

> Speaking of misunderstanding, that's certainly
> possible.
>
> How much overhead is "normal" and alternatively,
> why in FreeBSD USB 2.0 reports as "40MB/s" and
> not other arbitrary number.
>

The overhead includes many different things including hardware latency.
 However the big one is USB communication itself.  That is static, you
can't change it and it doesn't vary(assuming same communication type).
 Your reported speeds are typical, and in all likelihood would be very
similar under another OS.



-- 
Adam Vande More



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