While some devices use external power supplies, this is usually because the amperage over the USB interface is not enough to power the device entirely. The reason the external power supply may be 12v instead of 5v is simply because they are going to make it whatever most convenient to them.

Some of these cables are very very thin, and I can’t imagine them being able to carry even 12 volts without self-destructing.

Patrick, does the usb specification include a minimum voltage the insulation has to suitable for?

Raising the voltage allows much higher wattages, but it does increase the component count on the powered device, as it will need to step the voltage down, and the current up, to meet the requirements of the devices. Although the device would probably already contain a voltage controller to handle any voltage drop due to the resistance of the cable.

Using USB2′s 1.5 amp cables and 100v would give 150w theoretical and not require anymore connectors. The raise in voltage would be negotiated just like everything else, to ensure nothing was electrocuted.

Up to 120VDC is classed as ‘extra low voltage’ and so would not require any significant differences than using 12v, so long as the insulation was sufficient.

The CPU time usage comes from USB host controller being set up to be minimal in terms of hardware to make software pick up the slack to ensure maximum flexibility for the interface. The software running the host controller could be run on another CPU in a multicore system, or even a dedicated microcontroller if the hardware designer was so inclined, but that comes with its own issues.

With that off my chest, onto the issue! The problem it seems you with to address is that we have no standard for an external DC power system. We have the de facto standards of 12V, 5V, and 3.3V inside a PC case, but none for the outside. Computer modders have thrown themselves at this problem but none of the solutions are truly what it seems you are suggesting. The idea is for power management to the device as well as monitoring and overcurrent protection. Maybe the dice could take the power from firewire 
I think this could be done and still fit in the standard USB connector. How this would work is that the device connects to USB as normal and the host controller reads the power requirements from the appropriate descriptor as normal. When the device requests ‘powered USB’ support, the controller signals a power controller to connect the device to the larger power source. If the device is connected to a hub that supports powered USB, the host controller would send a command to the hub (though an extended hub class) and the hub would manage its local power circuitry. If the hub can’t support powered USB, it would report back and the user could be informed that hub is not powered USB compatible.

The last thing that bothers me is your proposal for ‘USB 3’. At is currently stands, USB 2.0 is based on an EHCI which does not support USB 1.1, UHCIs or OHCIs do that now. When you plug in a device, one of the first things it does is negotiate to connect to the EHCI, or stay on the OHCI/UHCI. The ‘beauty’ of the system was keeping the same software stack. This is important to the OS developers. Ask them to start from scratch and they will refuse. Another example of this is PCIe. If you look at PCIe vs Infiniband, they look a lot alike. What made the industry come down on the side of PCIe is that it uses the PCI software specification. As odd as it seems, it is easier to change the hardware than the software.

What hinders USB3 is that standard USB 1.1 compliant cables can only carry 0.5A, and USB 2 cables are only supposed to carry 1.5A max (and most probably fail that test).

USB3 simply cannot support asking for more than around 1.0A without putting users and other devices in danger.

Also, yes, it does look like a normal USB connector. Its a dual section plug, the top half is a normal everyday USB plug and accepts both regular USB plugs and New Powered USB plugs. See the image I included in part 2 of this article for a standard Powered USB plug (not the New kind because they don’t exist (yet)).

(if it don’t look like an normal usb connector it isn’t really “usb”…. the world is ugly as it is with a/b/mini/micro)

So far it sounds like PoE isn’t a strong contender but it has one feature that USB and Firewire don’t supply, device sharing. There is also less of a problem with mixing different speed devices, all switches can handle mixed speeds 10k,100k,1m.

Price is a problem though, rj45 connectors are much more complex to manufacture than USB.

The sharing abilities do cause problems though, the keyboard and mouse would need to be on a seperate bus or ‘paired’ in some manour with the computer.

Thanks in advance,
Pete

And no, I don’t think its right to have high and low bandwidth devices segregated by using different busses. Look at how I solved that with USB 3, USB 2 devices will use the legacy interface all to themselves, while USB 3 devices will use the new interface all by themselves.

They will be segregated in the same connector.

So you fix USB by making USB 3.0 into a firewire with a new formfactor?

Adaptors may be a bad idea, but so is putting a second set of connectors on. That’s going to be an easy plug to break when it gets built cheaply and somebody’s grandfather starts pulling it out by the wire.

However, you’re missing another important feature of Firewire that USB misses. (Look carefully at the communications protocol.)

Anyway, I personally think that, if we’re going to have to invent another plug, why invent a USB 3 when Firewire already does the job? If you figure Firewire has made too many enemies or some such thing, there is always serial SCSI.

Low speed devices and high speed devices should be on separate hubs, and that means it is _correct_ to have USB and Firewire as separate interface standards.

Don’t understand why? I have a Mac Mini, it has two USB ports, I hang a USB2 hub off one to plug in my cheap PC keyboard and mouse. With those plugged in, my USB2 2.5 inch HD can’t operate as a USB2 device, and falls back to USB1 speeds and protocols. Does that help explain why universal is not the answer to everything?

I know iNTEL would love to have it’s own devices be the universal solution, but that kind of behavior leads to the kind of silliness they pulled with UWB. The Motorola solution was better, lower power, less interfering. Motorola offered it free. iNTEL turned their corporate nose up at it. You could have gotten rid of all your data wires entirely, without leaking your data to anything sniffing nearby.

Give USB a rest. It does keyboards, mice, cheap printers, wacom style tablets, scanners, and such just fine. (Well, the tablets, mice, and keyboards, anyway.) Disks really belong on Firewire or better.