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 add an adapter card or turn the computer off. The first USB 1.1 peripheral bus standard was developed in 1997 and the technology was made available without charge for all computer and device vendors (USB, TechTarget). Starting in 1996, a few computer manufacturers started including USB 1.1 support in their new machines. However, it wasn't until the release of the best-selling Apple iMac in 1998 that USB became widespread.
USB 1.1's speed was insufficient to support the most demanding PC user applications, such as digital image creation and web publishing, where multiple high-speed peripherals will be running simultaneously (Universal Serial Bus - FAQs). As a result, work began on USB 2.0 which would deliver speed forty times faster than USB 1.1. The USB 2.0 spec was released at WinHEC in April 2000. Another new USB standard, USB On-The-Go (OTG), made an initial appearance in the market 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 to fit the mobile form factor and lower power features to preserve battery life.
General Operation and Environment
The intent of the USB architecture is to provide a replacement for the aging serial and parallel ports on existing computers (Rehak, 1999). Those ports impose limitations such as cable length, cable size and complexity. Unlike older ports, USB uses one interrupt request no matter how many devices are in use and it offers instant plug and play for its device set. After loading the device software the computer user can plug the physical device anywhere in the USB network and it will work. The unit can be plugged in to a different port each time with no consequence. And, the flow of information in USB is more like an advanced data network protocol than the traditional PC serial bus data flow. It provides a way to funnel information from many devices into and out of a computer system in an orderly manner.
USB uses a hub architecture (Rehak, 1999). Hubs are what are connected, hubs connect to hubs. A maximum of 127 devices can be attached to a 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. USB 2.0 is fully compatible with USB 1.1 and uses the same cables and connectors (Universal Serial Bus - FAQs). With a speed of 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 like devices. Game paddles, joysticks, steering wheels etc. can be attached to the USB port. Devices such as monitors, speakers and LANS will require the higher speed option. Devices that do not need a lot of power, like digital cameras, can draw their power from the bus. That means they operate without a wall plug.
USB 2.0 quickly replaced USB 1.1 which had already become a ubiquitous connector on PC systems for such peripherals as 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 will be USB 2.0-enabled. As the standard is adopted by notebook PCs and, eventually, PC peripherals and consumer electronics devices, the total number of USB-enabled devices will increase from approximately 375 million in 2002 to 863 million in 2007, a CAGR of 18.2%. In-Stat/MDR has also found that:
PC peripherals that require higher speeds have begun to adopt USB 2.0, including hard disk drives, optical drives, and scanners. Other PC peripheral devices, including printers, hubs, and PC cameras, will also adopt USB 2.0 in time, but have been slow to do so because they have slower speed requirements.
Consumer electronics devices will adopt higher speed USB 2.0 at a slower rate than PC peripherals, but most will eventually adopt the new standard. Many of the devices in this category are not as closely tied to the PC as the peripheral market, and often do not have higher speed requirements. The emergence of less expensive embedded USB 2.0 solutions, as opposed to discrete solutions, will help to drive its adoption in these types of markets
Refer to the figure below for a summary of USB adoption and a forecast for the future.
Supporters of the Technology
Universal Serial Bus was developed by a complex of companies (Compaq, Digital, IBM, Intel, Microsoft, NEC and Northern Telecom) with the aim of using a single interface to connect accessory peripheral units, thus replacing parallel and serial ports as well as other inputs and output on computers (USB, TechTarget). In 1995 the USB Implementers Forum (USB IF) was set up to support and speed up use of USB peripheral units by the market and consumers (About USB Implementers Forum, Inc.). USBIF is a non-profit corporation founded by the group of companies that developed the initial Universal Serial Bus specification.
The USB 2.0 spec was developed by a team of seven industry-leading companies, collectively named the USB 2.0 Promoter Group (Universal Serial Bus - FAQs). The group consisted of Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC, and Philips. Companies contributing to USB On-The- Go include Advanced-Connectek, Cypress Semiconductor, Ericsson, Hewlett-Packard, Insilicon, Intel, Marunix, MCCI, Microsoft, Mitsumi, Molex, Motorola, NEC, Nokia, On-spec, Opti, Palm, Phillips, Qualcomm, Softconnex, Texas Instruments and Transdimension (USB On-The-Go).
The Firewire, or IEEE 1394 standard, by Apple, is another standard that defines a high speed serial bus. Originally USB 2.0 focused on connecting PC peripherals and IEEE 1394's target was audio/visual consumer electronic devices such as digital camcorders, digital VCRs, DVDs, and digital televisions. Therefore, the two connections initially differed in primarily in application focus. However, upgrades to both technologies began interface competition between the two (Overington, 2002).
According to Overington, USB has in its favor the backwards-compatibility with USB 1.1 hardware and native support from Intel which will ensure a rapid uptake from hardware manufacturers. Peripheral manufacturers have already released USB 2.0 PCI cards and hubs, while motherboards based on Intel's i845 chipset all ship with on-board USB 2.0.
However, Overington believes that Firewire has many advantages over USB. For example, FireWires's transfer rates of 800 megabits per second outpace USB'a 480 megabits per second.
IEEE 1394b also benefits from stronger signal sent along the copper cable, which enables devices to be located up to 100m down the line. Unlike USB, FireWire is a multi-master bus system, more than one device initiating transfers can be active in the system.
Furthermore, IEEE 1394b has added robust control codes and scrambling of both control and data symbols to minimize cross-talk. Despite its technology advantages, the fact that IEEE 1394 is still not supported on-board by PC motherboard manufacturers will prevent it from gaining a decisive upper hand over USB.
Apple outraged chip and system manufacturers in early 1999 when it proposed a licence fee of $US1 per port for FireWire systems. The scheme was later dropped, but not before Intel shifted its weight…