Most motherboards these days come with 4 USB 2.0 posts on the back. The USB 2.0 speed is ~57MB/s.
My question is do all 4 ports on the back share that bandwidth, are they like a mounted hub?

What about if you add a USB PCI card, will those ports also share bandwidth with the other native ports?

Hope the question is good enough. Thanks for any feedback.

The usb ports are independent till you reach the limit accepted by the southbridge.

If a mobo says it supports 6/8/10/12 ports, then that number of usb devices will run at full speed.

If you use a pci card, it will run trough pci lanes and nothing has to do with the usb ones.

The only way to share bandwidth is with a hub plugged at one usb port

thanks dude

A mobm may have 6-12 ports but only have less usb controllers also there is chipset bandwidth limits + cpu over head.
A pci card may have less cpu over head.