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Universal serial bus, a connection technology for attaching peripheral devices to a computer, providing fast data exchange.USB is aimed at peripherals connecting outside the computer.
UNIVERSAL SERIAL BUS(USB) INTRODUCTION TO USB USB is aimed at peripherals connecting outside the computer. USB supports easy connection of slow to high speed peripherals to your computer. The operating system supports USB. NEED FOR USB Printers connected to parallel printer ports, and most computers only came with one. Modems used the serial port, but so did some printers and a variety of odd things like digital cameras. Devices that needed faster connections came with their own cards, which had to fit in a card slot inside the computer's case. FEATURES OF USB The computer acts as the host. Up to 127 devices can connect to the host. Individual USB cables can run as long as 5 meters With USB 2.0,the bus has a max. data rate of 480 Mbps. A USB cable has two wires for power and a twisted pair of wires to carry the data. USB FEATURES CONTINUED On the power wires, the computer can supply up to 500 milliamps of power at 5 volts. Low-power devices can draw their power directly from the bus. High- power devices have their own power supplies and draw minimal power from the bus. Hubs can have their own power supplies to provide power to devices connected to the hub. USB devices are hot-swappable. USB CAPABILITIES EASY TO USE EXPANDABLE SPEEDY USB DEVICES Printers Scanners Mice Joystick Digital cameras Webcams Telephone Modems Speakers Storage devices such as Zip drives USB CONNECTIONS The rectangular socket is a typical USB socket on the back of a PC. USB CONNECTIONS CONTINUED A typical USB connector, called an "A" connection. "A" connectors head "upstream" toward the computer. A typical “B” connection. "B" connectors head "downstream" and connect to individual devices. RUNNING OUT OF PORTS? Most computers come with one or two USB sockets. With so many USB devices on the market today, you easily run out of sockets very quickly. So the obvious question is, “ How do you connect all the devices? ” SOLUTION The easy solution to the problem is to buy an inexpensive USB hub. A TYPICAL USB 4-PORT HUB ABOUT HUBS A hub typically has four ports, but may have many more. By chaining hubs together, you can build up dozens of available USB ports on a single computer. Hubs can be powered or unpowered. The hub has its own transformer and it supplies power to the bus so that the devices do not overload the computer's supply. USB TOPOLOGY USB CABLE The devices connected to a USB port rely on the USB cable to carry power and data. Inside a USB cable: There are two wires for power -- +5 volts (red) and ground (brown) -- and a twisted pair (yellow and blue) of wires to carry the data. THE USB PROCESS ENUMERATION TYPES OF DATA TRANSFER Interrupt - A device which will be sending very little data, would choose the interrupt mode. Bulk - A device which receives data in one big packet, uses the bulk transfer mode. Isochronous - A streaming device uses the isochronous mode. WINDOWS SUPPORT USB 2.0 USB 2.0 provides additional bandwidth and has a data transmission speed 40 times faster than USB 1.1. USB 2.0 is fully compatible with original USB devices. Supports three speed modes. USB 2.0 supports low-bandwidth devices, high-bandwidth devices and high-capacity storage systems. CONCLUSION USB is all about convenience. A user of a USB device sees a piece of hardware that is a “no-brainer” to use. USB is enjoying broad adoption in the marketplace today. Thousands of devices have passed compliance testing.
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