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Old 04-26-2005, 05:28 AM   #1 (permalink)
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Default USB 1.1/2.0 bus..

I have an ABIT IC7-G motherboard with a total of 6 USB ports (I think it actually has 8 but what ever) and wondered how the USB bus was setup. Since I know for a fact that with one USB port (even for USB 1.1) you can daisey chain it for up to 127 devices. And with those 127 devices the bus has to be split 127 different ways. So thats either 1Mb/127 or 12Mb/127 depending on how far away the devices are. So it's obivous that having even one external HDD on USB 1.1 would be a bad but having more than 1 would be a nightmare. Now with USB 2.0, spliting it up wouldn't be so bad but still bad.

So here is my question; Since I have 6 USB ports coming right out of the motherboard instead of 1 or 2 like back in the Pentium/PII days, I want to know if each USB port on the back of the computer (or front) has a dedicated 480Mb bus or is it that that bus is 480Mb split up amongst 6 dedicated ports on the front/back of the computer?

I mean since I have a totally separate cable coming out of the 5/6 pin connectors to hook up into each of the USB external port/separate soldered I/O ports on the back of the motherboard that they would have a dedicated bus. With logic you would think they would have a dedicated bus per port but because of the design of the PCI bus for example where it's split up amongst devices, I'm worried that this is so with USB 2.0/1.1.
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Old 04-26-2005, 07:40 AM   #2 (permalink)
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i couldnt say exactly, although my educated guess would be that they are split up over the same bus, so you get x/480mbit at any given time, if you had 2 devices plugged in, and were using both at the same time, it would be split up so they each get a share of the bandwidth. but if you had 2 devices plugged in and were only using 1 it would get all the bandwidth.
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Old 04-26-2005, 10:05 AM   #3 (permalink)
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USB 2.0 at 12mb? what are you talking about?

USB 1.1 low speed = 1.5 Mbit (192 KBytes)
USB 1.1 Full Speed = 12 Mbit (1.5 MBytes)
USB 2.0 Hi-Speed = 480 Mbit (60 MBytes)

Not all USB 2.0 devices are Hi-Speed!
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Old 04-26-2005, 08:43 PM   #4 (permalink)
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...one USB port (even for USB 1.1) you can daisey chain it for up to 127 devices. And with those 127 devices the bus has to be split 127 different ways. So thats either 1Mb/127 or 12Mb/127 depending on how far away the devices are...

I was thinking of USB 1.1 when writing that sentence which is why I choose to say 12Mb and 1Mb. Yes you are correct, it IS actually 1.5Mb but thought it wasn't very significant anyways.
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