Why Powered USB Is Needed, Part 2: The Future of USB

This article describes a version of USB that is not related to the new USB 3 spec that Intel has released for 2010 products

The Universal Serial Bus, or USB, is right now the most common serial peripheral bus in existence. Allowing all the most common devices to connect to your computer, to each other, through hubs, and now even wireless USB has become the dominant method of low bandwidth communications between devices and their peripherals.

However, USB is not without flaws, in fact, it has tons of issues that other less accepted standards have already solved, and USB has either not solved them or solved them only recently. One of those problems is that, although USB does provide electrical power to peripherals, it is rarely enough to run devices that suck juice like no tomorrow. Powered USB exists to solve this problem.

I will tell you why Powered USB will never be widely accepted, and also why we need it. However, to do so, this article is split into two three parts: the first part discusses the history of USB and previous peripheral ports, and why it it became widely accepted, the second part contains the meat of my argument on why Powered USB is both needed, yet failing to be accepted, and the third part describes a possible future USB 3 specification in detail.

This is part 2. Part 1 is available here, and part 3 is available here.

Short Introduction to Powered USB

At the end of Part 1, I said USB does not provide enough power for certain devices, a total of 2.5 watts at 5 volts. This is enough for any device that uses little power: keyboards, mice, USB flash keys, etc, etc. Compared to Firewire 400, which can provide similar data transfer performance to USB 2.0, devices can use up to 45 watts at 30 volts.

Powered USB can output 144 watts at 24 volts, 72 watts at 12 volts, and 30 watts at 5 volts (all at 6 amps current), while Firewire does up to 45 watts at up to 30 volts (1.5 amps current), and USB 1.1 and 2.0 does 2.5 watts at 5 volts (500mA of current).

According to recent comments of this article, my original math was wrong: at 24 volts Powered USB only provides three times more power than Firewire, and at 5 volts Powered USB provides five times more power than normal USB.

In Firewire 400 against USB 2.0, Firewire comes out as the better bus for many devices due to the fact that it can supply enough power to, for example, run a two or three drive enclosure or an external DVD burner; not only that, it does perform better than USB 2.0 for data transfers due to the fact you can never get 480mbps transfers in the real world, only around 240 to 360mbps, whereas on Firewire 400 you really can get to 400mbps.

Firewire, for devices that require power and bandwidth, gives USB 2.0 a severe beat down but has trouble taking on Powered USB.

Don’t understand how much power 144 watts at 24 volts is? You can drive printers, scanners, large RAID enclosures, multiple DVD burners for parallel/mass burning, even medium sized LCD monitors. You could drive a pair of large speakers with this much power in addition to sending them digital sound to play.

As you can see in the image, the top part of the plug is the power plug combined with the bottom part of the plug that is a standard USB data plug. This power plug’s power output not being standardized is where everything goes wrong.

The plug did it with the crowbar in the library

The Powered USB specification manages the second half of this (very ugly) plug, where all the extra power comes from. According to the specification, you may have different layouts of power pins to supply 5, 12, or 24 volts, and each plug can only do one of the three.

Can you imagine how confusing this would be to end users? Powered USB has gone back to the days of having incompatible but similar functioning ports on the same computer. Had problems telling your grandmother about PS/2 and SCSI ports, and why she can’t plug her printer into either? Now tell her why she can’t plug her PUSB-5v device into a PUSB-12v plug.

USB does need a powered extension to compete with and possibly eliminate Firewire. I have a dozen devices that have separate power cords and power bricks and it makes for cable spaghetti behind my computer. If all my devices supported some sane future form of Powered USB, I’d lose at least four or five of these power cords.

So how can this be fixed?

For New Powered USB to move forward to the home desktop, I envision that both the USB Working Group and the Powered USB Working Group needs to release new versions of their specifications. First, Powered USB needs a new version (lets call it New Powered USB): they have to standardize on one voltage. I suggest using 12 volts, or use a floating voltage design like Firewire does (12 to 30 volts instead of 30 volts fixed), as this would be most beneficial to devices that require high voltages.

Second, I suggest the USB Working Group should release USB 3.0 already. As I mentioned before in this article, Firewire 400 is marginally faster than USB 2.0, however what I did not mention is that Firewire 800 is about three times faster than USB 2.0 and is already available in a couple devices. I expect to be able to do at least 800mbps or 1600mbps of real performance (akin to USB 2.0’s 240-360mbps real performance) or even more.

Third, I suggest that power strips (the kind you plug your computer into) add USB to New Powered USB bridges that simply pass the USB data over, but add the power pins and power the devices directly from the power strip. Adding these plugs would allow people to power new devices with older computers or with smaller devices (ultra-small laptops, PDAs, etc) that can’t power devices on their own.

With these three suggestions, I can bet you that New Powered USB would become a common home standard, and at least part of the cable spaghetti problem would go away, and I can also bet you that Firewire might also disappear as well.

Continue to part 3.

Written by
Patrick McFarland
Open Source software architect and technologist. He's just this guy, you know? Follow him him on Google+.
Published in
Ad Terras Per Aspera
Transmissions from the Little Blue Marble

Published March 30th, 2007

Comments

70 Responses
1 2 3
kirchoff
March 31, 2007 at 12:41 pm | Reply

>>All three of these allow up to 6 amps of power, compared to USB’s 500mA. That is 12 times more power at more realistic voltages for larger items, and 8 times more power than Firewire’s 1.5 amps.

You’re confusing power and current. Power is measured in watts, current in amps. Power is related to the current and voltage that a device can produce (or consume) by

P=IV

where P=power, I=current, V=voltage. So the proper way to say this is that PUSB can put out 12 times more current than USB2 can (both at 5V), and therefore it can produce 12x the power. Comparing current at different voltages is pretty useless — total power (Watts) is a better comparison.

Bryan
March 31, 2007 at 12:25 pm | Reply

Why not just have the wall outlet plug be the standard and use the powerline standard for data transmission over your home’s existing wiring?? Then you could plug devices in anywhere and you just have a buch of standard plugs in the back of your computer, kind of like the cable box does for connecting your tv so you just turn the cable box on….

my 2 cents

Laurent Debacker
March 31, 2007 at 12:18 pm | Reply

> Powered USB is the last thing we need. Computers are already using too much power. The environmental impact from using all that electricity will be devastating.

You’re jocking, right? If you buy a hard-disk, it needs power. Be it from a power brick or powered usb, it will obtain its energy. The impact of Powered USB is only that it is more convenient.

Dom De Vitto
March 31, 2007 at 12:15 pm | Reply

Why not just keep with the existing pinouts, but have powered USB devices negotiate what voltage, and current the system should drive to?
For instance, a DVDRW doesn’t need much power when it’s not reading a disk, more more when it’s reading, and lots more when it’s writing. With the m/b dynamically arbitrating and acknowledging if the device can have the power, you’ve the best of all worlds, plus:
Same pinout – compatibility with old devices, new devices can ‘just work’ with old USB controllers, but need external power.
Any voltage your controller can supply is supported, not just 5/12/24/30. Graceful failure for the device – requiring a separate PSU.
Seamless upgrade/downgrade, old devices work on new controllers, and new devices work on old controllers.
Hay, you could even have three DVD burners, and have power for burn on two, and read on the third etc. USB1 controllers all know how much power is being consumed, so telling the device can’t be ‘hard’….

Kevin
March 31, 2007 at 12:15 pm | Reply

>>When the grandmother is trying to put the Powered USB cable into the computer, she’s already bought the peripheral unit (meaning it’s too late).

I’m still not confused. If your Powered USB plug doesn’t fit into the USB 2.0 socket, then there is something wrong. It’s either time to upgrade your computer, or else you should check to make sure that the random peripherial that you purchase is actually compatable with your computer. Preferably BEFORE purchasing it.

Would you buy a new stove without first checking to see if it’s gas or electric? Does anyone nowadays honestly think that any piece of equipment on a store shelf is compatable with everything else?

>>Can you tell the difference immediately between the two plugs?

Yes.

>>What if the ports weren’t colored?

Even if it’s pitch black in the room it still won’t fit.

>>What if I can’t clearly see the sockets? Surely you’ve accidentally plugged your PS2 mouse into your keyboard port, and vice versa?

Yes I have, but according to this spec that’s not a problem because it still won’t fit in the wrong socket. I’m also doubtful that you can count the number of available USB 2.0 sockets better without seeing them than the number of powered USB sockets without seeing them.

>>What if I have all of my ports filled with devices, and I want to buy one more? Why should I, as an end user, have to keep track of which “round” “square” and “triangular” pegs I need?

This is a legitimate complaint due to inconvenience factor. But it doesn’t lead to confusion for smart people. That’s all I’m saying.

It is entirely possible for Powered USB to fail due to inconvenience factors, or by confusion of the techonophobes. And perhaps it is an inferior spec compared to the alternatives. But for those of us with half a brain we can at least figure out how to use this stuff.

JasonG
March 31, 2007 at 11:49 am | Reply

Hi-Speed USB is so slow because it is like PIO mode hard drive transfers. Just check out your CPU usage whilst doing some large file transfers.

Terrible!

Firewire, properly designed, uses very little CPU, even at full tilt during a transfer.

The principle reason for USB “winning” it’s cheap! This why everything wins. People won’t pay an extra buck for something far better, if there exists something good enough, even if it sucks.

Stupid people! Short term gain is long term loss in most cases…

andrey
March 31, 2007 at 11:44 am | Reply

Exactly the last thing we need is more cables, and less efficiency.

Down with Inefficiency! Enjoyed the article.

Greg
March 31, 2007 at 11:44 am | Reply

Actually Powered USB should result in energy savings. The always-plugged in power bricks used on most peripherals have a continuous draw of 2-5 watts, even when they are not in use — this is known as plug load in the industry. For example, a single brick continuously pulling a mere 3 watts uses 26 kWh annually. If one were able use Powered USB, the devices would be powered only when needed, and I also suspect that the better PC power supplies are more efficient than the power bricks, which will provide additional savings when the peripheral is actually in use.

pmh
March 31, 2007 at 11:43 am | Reply

A common power supply is usually more efficient than having each device convert power from AC using it’s own power supply and MUCH more efficient than leaving a wall wart plugged in all the time. I’ve seen electricity bills go downby 20% for the same networking equipment when they switched to using a common 48V power supply. Wall warts use small amounts of electricity even when they are not powering anything. Environmentalist’s luddite complaint is actually less environmentally friendly than powered USB would be.

Mike H.
March 31, 2007 at 11:34 am | Reply

>> Or maybe she should hire someone smart enough to upgrade her machine? If you’re confused by “Powered USB plug goes into the Powered USB hole” then you deserve to pay for tech support.

All of the Powered USB plugs will be ‘square.’ The difference will be a small keying notch to prevent a 12V device being plugged into a 24V socket. Glance at keys on here .
Can you tell the difference immediately between the two plugs? What if the ports weren’t colored? What if I have all of my ports filled with devices, and I want to buy one more? Why should I, as an end user, have to keep track of which “round” “square” and “triangular” pegs I need? What if I can’t clearly see the sockets? Surely you’ve accidentally plugged your PS2 mouse into your keyboard port, and vice versa? My parents have plugged an RJ15 into an RJ45 before. That actually fits, and even “clicks” in if you do it correctly.

These things are probably incompatible, and keyed due to the engineering challenge involved in using selectable VRMs.

Hobbes
March 31, 2007 at 11:33 am | Reply

Kevin, you are being an idiot making a point about that.

If powered USB is going to have different cables for each voltage then it’s going to add complexity and confusion, no matter how smart(ass) you are.

Kwilliam
March 31, 2007 at 11:32 am | Reply

I wonder: would powered USB be dangerous? I’d hate to electrocute myself by touching a USB port. Hopefully it only applies power after some data transfer, in which the device asks for X amount of power.

@ Environmentalist: Powered USB wouldn’t increase the amount of power our devices use. I can promise you that unless another century of oil is magically discovered, power efficiency will continue to be improved. Consider: LCD displays and new solid state disk drives don’t use near as much electricity as old CRT monitors or spinning disk hard drives. The only peripherals I can think of that need a lot of power by design are printers and giant speakers.

@ Kevin: Admit it, you secretly like the idea of just one plug for everything. Everyone does. It’s convenience! Having multiple plugs is a scheme used by the cable manufacturing industry to force users to buy lots of additional cables. (Consider the number of different “mini” USB ports out there.)

Lastly, Dude! Does this mean my refrigerator will finally be able to connect to the Internet? (lol)

Patrick McFarland
March 31, 2007 at 11:30 am | Reply

fryke: Actually, USB doesn’t have to go through the CPU. In the case of real USB 1.1 controllers that use OCHI, it works the same way as Firewire’s OCHI.

The only thing missing is the direct memory access over Firewire ability, which is usually “safetied” in various ways which in turn increase security but decrease speed.

EHCI, however, works like UCHI (afaik), thus is more software driven.

DV cams are only depending on the low CPU transfers and the raw speed. USB 3.0 as I proposed would work just as well.

Environmentalist: Just the opposite. PSUs in computers are often higher quality and have a higher efficiency rating for voltage conversions than the power bricks many devices use.

Powered USB would actually increase efficiency, not decrease.

Kevin: The majority of customers are, unfortunately, computer stupid. If you want their money, you make products as stupid proof as possible.

T Knudsen: Imagine a powered hub without the separate power brick.

weatherwax54
March 31, 2007 at 11:28 am | Reply

thanks for a great summary, it’s a challenge to learn bits and pieces of tech without much context beyond what i need to know to do the specific task i want to do right now. i did wonder about the bitty plugs and why the one for the camera doesn’t fit the one for the mp3 player…

John Smith
March 31, 2007 at 11:27 am | Reply

>> Environmentalist, on March 31st, 2007 at 10:58 am, said:
Powered USB is the last thing we need. Computers are already using too much power. The environmental impact from using all that electricity will be devastating.

Their would be no difference, what powered usb is proposing is to do away with powering you devices through a wall socket and instead powering it through your computer.

Bj Raz
March 31, 2007 at 11:22 am | Reply

>>According to the specification, you may have different layouts of power pins to supply 5, 12, or 24 volts, and each plug can only do one of the three.

Keven, this is the issue not the plug its self

D
March 31, 2007 at 11:22 am | Reply

>> Or maybe she should hire someone smart enough to upgrade her machine? If you’re confused by “Powered USB plug goes into the Powered USB hole” then you deserve to pay for tech support.

Did you read the article at all? Each plug can only do one voltage. If Grandma has a printer that needs 30, she needs the 30 port. Now instead of simply having 8 USB ports, computers will need to have 8 USB and a handful at each power level. Ick!

>> Powered USB is the last thing we need. Computers are already using too much power. The environmental impact from using all that electricity will be devastating.

How wrong you are. Powered USB means that software can be written to minimize or hault power flow through the operating system, whereas traditional power cords and bricks require hardware-level interaction on the device themselves, something few, if any, peripheral devices actually do.

T Knudsen
March 31, 2007 at 11:20 am | Reply

I own an IOGear powered hub with a card reader. Am I in some way exceptional in this regard? I’ve bought them for friends at consumer electronics stores. I’m really missing the point of this article. Must be very nuanced.

T

Vegar
March 31, 2007 at 11:20 am | Reply

We are talking about compatibility here Kevin. When the grandmother is trying to put the Powered USB cable into the computer, she’s already bought the peripheral unit (meaning it’s too late). That’s when the grandson comes in trying to explain the grandmother “Why the fuck my god damn printer doesn’t fit in the friggin hole”. Standards exist so that you don’t have to take a bunch of technical details into consideration before your purchase. You not being an idiot should have grasped this idea before posting.

Bj Raz
March 31, 2007 at 11:17 am | Reply

if PUSB designers are going to read this article and take it to heart they will be fine. If they don’t then Firewire 800 will be a big change in the small picture, in the larger picture it will just be viewed as another change in ports.

Kevin
March 31, 2007 at 10:59 am | Reply

>>Can you imagine how confusing this would be to end users?

No, I can’t imagine, but then again I’m not an idiot. I guess I graduated past that kid’s game where you would put the round peg into the round hole, and the square peg into the square hole. If grandma’s Powered USB plug won’t fit anywhere into her computer but she’s still confused, then maybe she shouldn’t be using a computer.

Or maybe she should hire someone smart enough to upgrade her machine? If you’re confused by “Powered USB plug goes into the Powered USB hole” then you deserve to pay for tech support.

Environmentalist
March 31, 2007 at 10:58 am | Reply

Powered USB is the last thing we need. Computers are already using too much power. The environmental impact from using all that electricity will be devastating.

fryke
March 31, 2007 at 10:51 am | Reply

Why would you want Firewire to disappear. It works great, there are millions of DV-cams out there that actually require that bus (don’t want anything like USB which _always_ goes through CPU).

Novice_Geek
March 31, 2007 at 10:37 am | Reply

I agree with you all the way! Powered USB will never be successful if they don’t have a standard connector. On top of that, they need to stop making those stupid mini-USB connectors. I never have the right cables because these stupid connectors!

Anyway, this is a great article 🙂

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