I just discovered that my supposed usb2 hub (a portable one I've had for a long time) is not usb2 - I've got a usb stick I've been copying a load of big files onto, and for the hell of it, I plugged the stick into one of the usb sockets on the back on my iMac (congratulations on possibly the most awkwardly placed usb sockets ever...) - and the copying speed went up 4-fold.

So I'm getting a pukka 7-port usb2 hub now.

My question is: if I have a number of peripheries plugged into a hub, but none of them are switched on/connected (e.g. printer, scanner, camera cable etc.) does that have any effect on the transfer speed of my usb stick when it's plugged into the same hub? Obviously, as the hub is plugged into one usb bus, there's only so much bandwidth to spread around, but that should only matter if other peripheries are actually using it, yes?

Only if they are powered on and in use.

's what I figured. My current hub is just crap then. Having a 7-porter is going to save an awful lot of fiddling around the back of the iMac - I don't generally have more than one or 2 usb things running at once apart from the keyboard anyway. There are 4 usb ports on the iMac, but I expect they're not all on separate usb busses?

Good question. I found this out.

Seems there's one chip, so one bus. The first paragraph says different, but it's clarified later.

If you don't read it all I don't care. Condensed version, one chip, one 480 Mbps bus.

I'd say there's plenty of power it's just the bandwidth that would suffer with a lot of activity from different sources, plus the iSight, bluetooth, SD card reader, and IR receiver are all on it too. Keyboard and mouse also but that's insignificant.

Hahaha, my favourite line is: "(If you still don't believe me that there are 14 480mbps-capable ports on this chip, see page 671 in the datasheet.)" That's just showing off!

I remember this issue being raised years ago in relation to the laptops, which is why I suspected that just because you get 4 ports doesn't mean you get 4 separate buses. It only really matters when there's big data movement, and the only things I have on the usb bus(es) that do that are the led printer, the CD/DVD R/W (external) and the usb memory stick, and I don't use them at the same time.

I guess this answers my unasked question, though, which is: does it make any difference whether a usb peripheral is plugged directly into one of the iMac ports, or into an external (powered) hub using one of the iMac ports instead? The answer appears to be that either way, it's really sharing the same usb port with everything else, so it shouldn't make any difference.

The problem I've been having is that my current hub is (a) unpowered and (b) only usb1.1!

So once I get the new hub, I'll have my keyboard in one iMac port, my external DVD drive in the next, my external port in the next, and a spare. Then everything else can plug into the hub, which is well-designed such that you don't get that problem of fat usb plugs not fitting next to each other.