Burning 2 DVD simultaneously... slow

[Lennart Sorensen]

On Tue, Feb 22, 2011 at 09:04:52AM -0800, William Park wrote:
> How is USB3 different from USB1&2 ?  I thought they are using the same chipset, 
> except faster down the wire.

No, very different.  One of the biggest mistakes in USB1 and 2 was the
lack of an interrupt system.  USB 3 has interrupts.  So where USB 1 and
2 had to constantly poll devices to see if they were done, with USB 3
the device can simply send an interrupt when it has completed a task.
I believe USB 3 also adds some DMA capabilities (using the interrupt
system) which should help offload the CPU, which at 4.8Gbps is pretty
much required.

So USB 3 chips are completely new, although they have USB 2 and USB 1
backwards compatibility support, just as USB 2 was backwards compatible
with USB 1.  USB 3 also has new wires, in fact two pairs, one transmit,
one receive, so it is full duplex.  USB 1 and 2 has only one pair of
wires which is used to both send and receive (the other two wires in
USB1/2 are power).  USB 3 uses the power wires from USB1/2 and can do
some signalling as well as backwards compatibility work on the USB1/2
data line, while using the new signals for the high speed stuff.  Being
full duplex is part of what allows the interrupt system since there is
a dedicated path for sending messages to the host rather than having to
wait for the host to ask a question.

-- 
Len Sorensen
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