USB speed limited by PCI bus?

[martinarial]

Hi everyone!
This is my very first post, I hope it'll make sense so it doesn't waste anyone's time 😱)

My USB 2.0 ports have stopped working on my old Dell Dimension 2400...and it's ok because they have worked well for the past 11 years, this pc doesn't owe my anything lol

I'd like to install a 4-port USB card on one of my PCI expansion slots but I was wondering if in such a situation the PCI bus would limit the speed of the USB ports?

It is my understanding that the PCI bus speed is 133Mb/s or 266 Mb/s depending if the bus runs at 33MHz or 66MHz (which I don't know in my case) but the USB 2.0 runs at 480 Mb/s...won't my file transfers from USB to hard disk and vice-versa be limited to the 133 or 266 Mb/s speed or the PCI bus, as opposed to a USB port that it integrated on the motherboard?

Thanks in advance for your clarification!

 

[WyomingKnott]

PCI 33mhz bus speed is 133 MB/s (mega Bytes), not 133 Mb/s (mega Bits). There's a huge difference. So, if I happen to be correct, your PCI connection should support two USB ports running at the top theoretical speed of 60 MB/s, or four running at the best speed I have ever seen.

Community, did I get my bits and bytes mixed up?

 

[martinarial]

Thanks WyomingKnott for the quick response! And you are right, I indeed got my bits and bytes mixed up, sorry!

I checked the technical specs on my pc and the PCI bus is 32-bit @ 33MHz, so its speed would then be 133MB/s, or about 1 Gb/s, which (like you said) allows for only two USB 2.0 ports @ 480 Mb/s each (totalling 0.960 Gb/s)...

So in order to be able to install a 4-port card my bus would have to be running @ 66Mhz, but it isn't, so I guess I'll have to install two 2-port PCI cards to get my 4 USB ports...gotcha!

 

[Alabalcho]

You should not worry about USB saturating your PCI interface. Whatever you're going to plug USB into, will be the limiting factor (aside from the fact that your 11yo CPU will get tired long before USB or PCI busses do so).

 

[WyomingKnott]

Not quite - I've never seen a USB device run anywhere near the theoretical limit. You could connect any 4 of my USB devices to that card's port and they wouldn't saturate the PCI connection.