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Posted by Bill's News on 01/22/08 00:16
"Peter D" <please@.sk> wrote in message
news:13p9pfbrchlpi54@corp.supernews.com...
>
> "Ilya Zakharevich" <nospam-abuse@ilyaz.org> wrote in message
> news:fn0gu0$2end$1@agate.berkeley.edu...
>> [A complimentary Cc of this posting was sent to
>> Peter D
>> <please@.sk>], who wrote in article
>> <13p6sjndnmlji49@corp.supernews.com>:
>>> In real life USB maximum transfers peak at about 2/3 of that
>>> speed. If you
>>> research actual test results, you'll often see speeds max
>>> out at 1/3 of the
>>> max of 480 Mbps. Becasue USB creates a network where every
>>> device "chats'
>>> with the central "host" (the computer in most cases) USB 2.0
>>> requires more
>>> CPU prcesses than
>>
>> ... Sorry, but the *technical contents* of this is exactly
>> 0.
>
> You say that as if I shold care what you think. If you have
> Paypal, send me a quarter. I'll call you the moment I care.
> :-)
>
>> If you know WHY the throughput is not close to the
>> theoretical maximum, please explain.
>
> It's all there. I assume English isn't your first language. So
> here goes:
> The theoretical bandwith (400Mbit/sec) relies on perfect cable
> length, perfect cable materials, and perfect hardware acting
> perfectly while doing nothing else. The reality is that cables
> are not perfect, voltage and signals on the line(s) are not
> perfect, connectors are not perfect, hardware is not
> dedicated, and more than one item on the USB 'network'
> degrades performance. Multiple items (even if not in use)
> degrade performance even further. USB is inherently "busy" and
> "chatty". And that makes it useless for Vidoe transfer if
> Firewire is available.
> HTH
>
>
I agree with your analysis, but not your conclusion - here's
why!
I recently moved my LG BD/HD player to a USB2 external box -
using the internal slot for other SATA requirements. Some
Blu-Ray MPEG2 recordings deliver a higher bit rate than DV from
a camera. There is never a hiccup in the playback of these
videos.
I've several other USB 1 & 2 devices attached. The only time
I'm reluctant to run other apps, whether or not they use USB
devices simultaneously with video playback, is when playing
BD/HD MPEG4 - because my processor is barely in spec for that
horsepower, not because the USB channel can't deliver the bit
rate.
None of these video functions has, as yet, required 400 mbps
transfer. Rarely is even 40 mbps called for.
Transfers of large video files between internal HDD and external
USB2 HDD are typically sustained at >27 mBps (nearly 240 mbps).
During playback of HDTV or DVD via USB devices, it is not at all
uncommon to be also capturing HDTV via another USB2 device.
That's not to say that all USB devices are built to the same
standards. I've a small drawer full of Maxtor and other USB2
devices which at some point in their out-of-warranty lifetimes
rarely performed above 9 mBps on the same PCs.
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