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.