Universal Serial Bus (USB): Technology, Standards & Competition

Introduction to USB Technology

Universal Serial Bus (USB) is a plug-and-play interface between a computer and add-on devices such as audio players, joysticks, keyboards, telephones, scanners, and printers. With USB, a new device can be added to a computer without having to install an adapter card or power the computer down. The first USB 1.1 peripheral bus standard was developed in 1997, and the technology was made available without charge to all computer and device vendors (USB, TechTarget). Starting in 1996, a few computer manufacturers began including USB 1.1 support in their new machines; however, it was not until the release of the best-selling Apple iMac in 1998 that USB became widespread.

USB 1.1's speed proved insufficient to support the most demanding PC user applications — such as digital image creation and web publishing — where multiple high-speed peripherals run simultaneously (Universal Serial Bus — FAQs). As a result, work began on USB 2.0, which would deliver speeds forty times faster than USB 1.1. The USB 2.0 specification was released at WinHEC in April 2000. Another new USB standard, USB On-The-Go (OTG), made its initial market appearance in 2002 to address the growing need for devices to communicate directly with each other when a PC is not available (USB On-The-Go, USB Implementers Forum). The On-The-Go supplement addresses this need for mobile interconnectivity by allowing a USB peripheral to have: limited host capability to communicate with selected other USB peripherals, a small USB connector suited to the mobile form factor, and lower-power features to preserve battery life.

General Operation and Architecture

The intent of the USB architecture is to provide a replacement for the aging serial and parallel ports found on existing computers (Rehak, 1999). Those ports impose limitations such as restricted cable length, large cable size, and added complexity. Unlike older ports, USB uses a single interrupt request regardless of how many devices are in use, and it offers instant plug-and-play functionality for its device set. After loading the device software, a user can plug the physical device into any point in the USB network and it will work immediately. The unit can be plugged into a different port each time with no adverse consequence. Additionally, the flow of information in USB more closely resembles an advanced data network protocol than traditional PC serial bus data flow, providing an orderly way to funnel information from many devices into and out of a computer system.

USB uses a hub architecture (Rehak, 1999). Hubs connect to hubs, and a maximum of 127 devices can be attached to a single hub. The USB architecture is defined as an intermediate-speed bus. With USB 1.1, the bus operates at either 12 megabits per second or 1.5 megabits per second, depending on the attached device. USB 2.0 is an external bus that supports data rates up to 480 megabits per second and is fully compatible with USB 1.1, using the same cables and connectors (Universal Serial Bus — FAQs).

At 12 megabits per second, the typical devices attached to serial and parallel ports are excellent candidates for USB attachment (Rehak, 1999). These include most printers, modems, pointing devices, scanners, cameras, and similar devices. Game controllers such as paddles, joysticks, and steering wheels can also be attached to the USB port. Devices such as monitors, speakers, and LAN adapters require the higher-speed option. Devices that do not need a great deal of power, such as digital cameras, can draw power directly from the bus, meaning they operate without a wall plug.

USB Adoption and Market Availability

USB 2.0 quickly replaced USB 1.1, which had already become a ubiquitous connector on PC systems for peripherals including keyboards, mice, joysticks, removable storage, printers, and scanners. According to research firm In-Stat/MDR (PCs, Peripherals and Consumer Electronics Getting on the Universal Serial Bus), PC manufacturers adopted the new standard very quickly — to the extent that all desktop PCs shipped by the end of 2003 would be USB 2.0-enabled. As the standard was adopted by notebook PCs and, eventually, by PC peripherals and consumer electronics devices, the total number of USB-enabled devices was projected to increase from approximately 375 million in 2002 to 863 million in 2007, a compound annual growth rate (CAGR) of 18.2%.

In-Stat/MDR also found that PC peripherals requiring higher speeds — including hard disk drives, optical drives, and scanners — had begun to adopt USB 2.0. Other PC peripheral devices, including printers, hubs, and PC cameras, were also expected to adopt USB 2.0 over time, though more slowly due to their lower speed requirements. Consumer electronics devices were projected to adopt USB 2.0 at a slower rate than PC peripherals, as many devices in that category are not as closely tied to the PC and often do not require higher data transfer speeds. The emergence of less expensive embedded USB 2.0 solutions — as opposed to discrete solutions — was expected to help drive adoption in these markets.

References

About USB Implementers Forum, Inc. Retrieved November 15, 2003 from USB Implementers Forum Web Site:

Overington, M. (2002, July 17). Speed test. APC Magazine. Retrieved November 15, 2003 from APC Magazine Web Site: http://www.apcmag.com/apc/v3.nsf/0/2B6542579D78DD07CA256D44001A5F12

PCs, peripherals and consumer electronics getting on the universal serial bus. (2003, February 26). Retrieved November 15, 2003 from In-Stat/MDR Web Site:

Rehak, K. (1999, April 24). USB explained: Is the universal serial bus for you? Retrieved November 15, 2003 from North Orange County Computer Club Web Site:

USB. Retrieved November 15, 2003 from TechTarget Web Site:

Universal Serial Bus — FAQs. Retrieved November 15, 2003 from Intel Web Site: http://www.intel.com/technology/usb/faq.htm#Q4

USB On-The-Go. Retrieved November 15, 2003 from USB Implementers Forum Web Site: