04/24/05

Created by the PC industry consortium Compaq, DEC, IBM PC Company, Intel, Microsoft, NEC, and North Telecom, USB specification 1.0 and USB Device Class Specification1.0 defines the USB device. Released at 1995 Comdex, USB Specification 1.0 was the final version. Developing an Open Host Controller Interface (OpenHCL), a separate triumvirate of Compaq, National Semiconductor, and Microsoft defines the software and hardware for implementing the OpenHCL on Intel-based PCs. Called Universal HCL, Intel has a similar specification which applies to USB controllers and motherboards. With onboard USB connectors, Intel motherboards became available in mid-1996. By 1997, all computer classes now must support both USB specifications and either OpenHCL or UHCL. Freeing PC users from a limited number of free interrupts available for peripheral devices, USB eliminates the multiple peripheral connectors and tangle of cables behind PCs today. With a single twisted pair signaling, USB uses a four-wire connector plus 5-volt power and ground conductors. Limited to 12 Mbps with a 1.5 subchannel, the data rate is adequate for low-data-rate devices such as a mouse. Functionally, the low-speed subchannel helps to minimize chip cost and EMI protection requirements. Required for multiple connections to the host, USB hubs notify the host when nodes (called functions) attach or detach from the hub. Providing the dynamic reconfiguration and device identification required by Windows 95 Plug and Play specification, termination biased at each end of the cable provides attach/detach  notification  and identification of low speed devices. USB hubs can have seven connectors to a node or other hubs. Simultaneously attaching up to 127 devices to the bus with a five tiered star topology, the objective of USB is low implementation cost to minimize the premium for USB-compliant peripherals. Although 1394’s bus bridge might compare to a USB hub, 1394 allows up to 63 devices before a leaf node configuration requires a bus bridge. Having a signal rate of 12 Mbps, the USB can handle MPEG1, DVD 3.5 Mbps data rate, and MP@ML MPEG2 compressed video and audio at +6 MBPS. Dramatically, up to 40 times quicker or 480 Mbps, USB 2.0 transfers data much faster than USB1.1. For video capture devices and storage applications, USB 2.0 provides additional bandwidth.

http://www.ami.com/products/services/usb/1394usbcomparison.cfm