Benefit of powered usb hub vs not powered? and max hub per port?

ok for all sams club members, u know the slamin deals we can get on "accessory" chinese hardware. They have an acount with Straitec which makes nice Gold tipped usb cabled and hubs, they had a great powered hub and 2 packs of 10 ft gold plated usb cables (7$!!!) the hub was 16$.

now straitec has changed their product lineup, they offer a non powered hub designed for laptops and single cables now that come with a coupler for extending two cables (useless imho) and it is 5$. I know cables are cables, but i am one of those folks that has an eye for quality, and i spend it on cables.

Anyways I need another hub and my choises are between the straitec which is not powered and cheaper than BJ's WholesaleClub that has a GE usb hub which is powered for 17$ and comes with an extra cable. Also they have GE branded usb cable 3 pack 2x6ft and 1x10ft for 7$, not bad

NOW HERE IS MY QUESTION TO MY FELLOW HARDWARE GENIUS':

What benefit do you receive from using a powered hub?
Second, what is the max number of devices can attach through hubs to a single port. The ports I have on this machine are 4 built in on an intel MB, and two extra that plug directly into the board and rest in the pci spot

thanks for any advice

When using non-powered USB hubs, the power is drawn from the USB controller (either the mainboard or the addon card). The amount of power that can be drawn from the controller is rather limited. This is enough to feed small devices like cardreaders and mice, but not for the devices that need more power (like USB powered scanners).

Non powered USB hubs are nice for mobile use (less cables) or when you just need a few small devices on the USB bus, but they have a downside. Although modern software (like Windows XP) detects when you are "overloading" your USB bus, some hardware can't take it and becomes unstable. Although this isn't common, it's wise to use powered USB hubs whenever you can (unless you have good reasons not to, such as for mobile use).

The maximum number of devices? I'm not sure about this, but if I remember correctly, each controller can hold 127 devices. That's more than enough for most situations, right?

ok so stuff like usb powered scanners lights fans etc. got it.

but do you think a ac powered external hardrive or dvdrw uses the same power as a mouse? logically it should use less than a mouse?

also when u said 127 to a controller, a controller is the whole unit no a single port.

say you had a pci usb addon with 2 ports, you would get to add 250 or 127???


ps I got one of the bogus toshiba laptops (s149 series) with one geniune usb 2.0 port the other 2 is 1.5(some beta crap) I work for apple and our ipods are having probs with them, when i plug in my ext HD, windows gives me a message

127 addressable devices per controller, and the ports on a system are usually either 2 or 4 to a controller - not sure if the Hubs are also addressable devices

http://www6.tomshardware.com/consume...909/index.html - an interesting piece... - if you want to handle multiple, high throughput USB 1.1 devices, into a single USB 2 port, a Hub with only a single TT offers only a single merged USB1.1 throughput, while multiple TTs enable no-compromise USB 1.1 throughput to each device.

What I WAS looking for, was the hub depth limit - how far can you chain them!


The basics of the powered/unpowered issue are:
The maximum port load is 500mA (one "high power" load)

So with no additional power source other than the port, an unpowered hub is limited to:
4 low power (100mA) loads (typically USB keyboard, mouse etc.) - in a hub chain with more than 4 devices, the remaining devices must be self-powered.
It MAY be permissible to use a single high power device, and the remainder self powered.

My webcam is a high power device - that surprised me!