System Builder: The future of USB – General – How To


John Gillooly takes a look at what comes next for the most common of connection technologies.

USB first hit motherboards back in 1996, during the reign of Windows 95. It was designed as a next generation replacement for the serial and parallel interfaces of the time. Unlike these connections, which required the PC to be rebooted every time a peripheral was connected, USB was hot pluggable. It could also deliver power, meaning that small devices didn’t need external power bricks to operate.

But more than this, USB was the first in a raft of new technologies designed to endure the test of time. At that point in the PC’s evolution the original round of interconnect technologies were being hacked and tweaked to deliver speeds that were never intended. This led to a rethink of the way in which such technologies were designed, with a shift in focus to building technologies that could be evolved over time but still stay compatible with previous versions.

USB was the first, and then came such things as Serial ATA and PCI-Express. There is no electrical reason why you can’t plug a first generation USB device into the latest USB 3 port (though there will undoubtedly be driver issues) and it is this backwards compatibility that has allowed USB to flourish since its launch.

By ensuring compatibility, product manufacturers have been able to implement new versions of USB fairly easily. It has also meant that motherboard and system manufacturers have been able to be proactive, using third party controller chips to add new functions while they wait for Intel to integrate the technology in its chipsets. Intel has only added USB 3 support recently, with the Z77 and similar Ivy Bridge chipsets, yet we’ve been seeing motherboards and laptops with the tech for two years, and the connection is now commonplace on external storage devices.

Now that Intel systems have at least four USB 3 ports by default, we should start to see it flow out onto other devices. We’ve seen a Gigabyte keyboard with USB 3 passthrough, and  our video producer raves about his USB 3 card reader. External Storage may seem like the best use of the bandwidth but we expect more and more creative usage to emerge.

USB’s ubiquity is its major strength when it comes to the rate of uptake. Take its most recent competition, Thunderbolt, for example. To use a Thunderbolt device you need a computer with a Thunderbolt port, which means a selection of Apple products and an even smaller selection of very new Windows PCs. A USB 3 device will work, albeit slowly, on anything with a USB port. 
While there is no USB 4 on the horizon, there are still a few tweaks in the pipeline, aimed at USB 3. The first aims to maximise the transfer speeds seen with USB 3, and the second is aimed at evolving its use as a power delivery mechanism.

USB Attached SCSI Protocol
Designed to enable much faster transfers from external storage, USB Attached SCSI Protocol (UAS) is designed to allow SCSI commands to be sent over USB. Normally when USB transfers data it does so using what is known as a bulk transfer. This is where both the data and any accompanying commands are sent as a single stream of 64k blocks, which was fine for the relatively low bandwidths of USB 1 and 2, but delivers speeds noticeably slower than the 5Gbps maximum of USB 3.

What UAS does is bump up the number of these streams, while also decoupling the commands and putting them into their own stream. This not only increases the bandwidth available for transfers but it also means that commands don’t slow down data, and vice versa. This results in noticeably faster transfers, with speeds limited by the storage device, not the cabling.

Of course, this comes with a pricetag. UAS will only work if every part of the data transfer chain supports it. That means your PC’s hardware and software, as well as the device being connected. The software side is supported in Windows 8, while motherboard manufacturers have varying levels of hardware support for the technology.

As for devices, they are limited to a handful of external storage products for now, but with Windows 8 bringing support on the host side we expect to see the number increase over the coming months. If you do want a glimpse into the potential inherent in UAS, some USB 3 devices come with software that enables Turbo mode. This isn’t UAS, but is rather a means of increasing the size of data packets sent by USB to get around the problems inherent with 64k block transfers.

You’ll be able to properly use UAS once Windows 8 launches, as long as you have a supporting motherboard and USB drive.

Power
One aspect where USB has shone is power delivery. It has now become the international standard for mobile phone charging (Apple excepted), and there are numerous devices designed to use a USB cord plugged into a wall adapter for charging.

In fact, there is already functionality built into USB that allows clients to detect whether they are connecting to a USB port for data or if it is purely for delivering power. The device can then draw power based on this information, which is why some tablets will transfer data to a PC but only actually charge when connected to a wall outlet . 

The actual power delivery ability of a PC based USB port is pretty low, at only 4.5W in USB 3. This is enough to power laptop hard drives for example, but larger drives need external power to run. There are some laptops and motherboards that come with special ports designed to push extra power for device charging, but even these provide just enough power to charge handheld devices.

This trickle is about to become a flood, as the USB Implementers Forum has recently finalised the USB Power Delivery specification. This document outlines new standards for USB to deliver up to 100W of power, ten times the output of Intel’s Thunderbolt technology.

While 100W USB will make charging phones and tablets a snap, its real intention is to facilitate new usage and charging models. Its commonly-used example is a monitor or dock that uses USB to charge your laptop when you get home. It has potential to reduce the need for power boards and multiple adapters in our computing lives – your monitor, printers and other devices could all be powered by the cable connecting them to your PC.

As to when we’ll see this standard hitting actual products, it could still be a while. It was only finalised in July this year, and it is likely that actual implementation will take months to happen, and even then it won’t appear in products until next year. 



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