[plug] usb2 woody

[Craig Ringer]

On Sat, 2004-05-15 at 21:23, Shayne O'Neill wrote:
> 480mb thruput is pretty snappy.
> 
> better than a network h-drive on a 100mg net theoretically.

Indeed. Unfortunately, USB2 has 480 megabit per second _peak_
_theoretical_ throughput. Reality tends to be a _lot_ lower, though how
much varies by device and controller.

Ethernet, on the other hand, often hits a sustained 95% of theoretical
speed.

USB2 should still be considerably faster than ethernet, but ... not
anywhere near enough faster. FireWire tends to be a lot faster again
(even FireWire 400).

The 480Mb/s quoted speed for USB2 is IMHO quite misleading. It falls
into the same category as "100Mb/s" wireless networking - that is, sure
you can get that - in a perfect environment, with equal bidirectional
traffic, including all management packets and all other overheads as
throughput. Maybe.

After all, we're not sold "200Mb/s" or "2000Mb/s" ethernet, are we? A
dodgy vendor could make a packet - "onboard 2000Mb/s ethernet!".

Craig Ringer