Universal Serial BusBiotechnology at it’s finest…What is Universal Serial Bus?When was USB developed?Why Develop USB?Why Develop USB? (cont.)The Goal of USB: AccomplishedWhat about limited ports?Powered HubsUn-powered HubsFeatures (www.howstuffworks.com)USB ConnectionsHow It WorksThe Three USB Data Transfer TypesUniversal Serial BusWilke RenwickITE 100 P. HealyBiotechnology at it’s finest…What is Universal Serial Bus?USB is a single, standardized way to connect peripherals to computersThe USB connectors, usually on the back of the PC, allow the user to connect many different devices to the computer from modems to digital cameras.When was USB developed?Some of the world’s leading technology industries got together to develop a standardized way to connect computers and external devices. In 1995, USB was the resulting product released at a data transfer rate of 12 mbps.  USB 2.0 now runs at 480 mbpsWhy Develop USB?USB was a new technology developed in hopes of helping standardize and simplify the way external devices connected and interacted with the PC. Before USB, printers and zip drives both connected to parallel printer ports. Zip drives required high-speed connections to the computer, which provided limited speed and success. Also, because most computers only came standard with one parallel printer port, this was not a very practical situation.Why Develop USB? (cont.)Like the parallel printer port, the serial port was also used by multiple devices. First and foremost, modems were connected through the serial port. A variety of other devices such as Palm Pilots, digital cameras, and some printers, also required the use of this particular connection which, in most cases, was very slow.The Goal of USB: AccomplishedThe release of Universal Serial Bus eliminated the need for multiple ports of different sizes and shapes for all of the PC user’s different devices, therefore rendering the slower parallel printer ports and serial ports almost obsolete.Not only does USB standardize the connection of external devices, it is also very user-friendly, simple, and easy to use.There are 120+ different devices for sale today that use this technology including mice, speakers, modems, storage devices such as zip drives and flash drives, printers, and many more.What about limited ports?The solution to this problem is simple: buy a USB hub.Relatively Inexpensive (as low as $15)Hubs can be linked, potentially giving you unlimited USB ports to your computer.The biggest difference between types of hubs that is important to know when dealing with USB devices is between un-powered and powered hubs.Powered HubsNeeded when connecting multiple unpowered devices such as mice or digital cameras.These low-powered devices derive their power source from the bus.If too many are connected through a hub, the computer may not be able to handle it.Un-powered HubsUn-powered hubs can be used with any number of high-power devices such as printers and scanners that have their own power supply, thus not requiring power from the bus.Safe to use with low-power devices (mice, cameras, joysticks, etc.) as long as too many aren’t connected as once.Features (www.howstuffworks.com)120+ different devices can connect to the host, either directly or through a hub.The maximum data rate for USB 2.0 is 480 MbpsHot-swappableMany USB devices have a “sleep” feature in which the host computer and the device go into a power-saving mode.USB ConnectionsJust how simple is using USB? Very. Just “Plug and Play”If the device is new and has not yet been installed, your operating system will more than likely auto-detect it and ask for a driver. Then, you simply install the peripheral.If the device has already been installed, simply plug it in to the computer and they will begin to interact.The connection is simple and nearly impossible to get mixed up:USB “A” Connector: (heads upstream towards the computer)USB “B” Connector: (heads downstream to the device)How It WorksThe Universal Serial Bus process is simple:When the host powers up, it queries all of the devices connected to the bus and assigns each one an address. This process is called enumeration. The Universal Serial Bus divides the available bandwidth into frames, and the host controls the frames. Frames contain 1,500 bytes, and a new frame starts every millisecond. During a frame, isochronous and interrupt devices get a slot so they are guaranteed the bandwidth they need. Bulk and control transfers use whatever space is left (at least 10%).The Three USB Data Transfer Types-Interrupt - A device like a mouse or a keyboard, which will be sending very little data, would choose the interrupt mode.- Bulk - A device like a printer, which receives data in one big packet, uses the bulk transfer mode. A block of data is sent to the printer (in 64-byte chunks) and verified to make sure it is correct. -Isochronous - A streaming device (such as speakers) uses the isochronous mode. Data streams between the device and the host in real-time, and there is no error correction. -As devices are enumerated, the host is keeping track of the total bandwidth that all of the isochronous and interrupt devices are requesting. They can consume up to 90% of the 480 Mbps of bandwidth that is available. After 90% is used up, the host denies access to any other isochronous or interrupt devices. Control packets for bulk transfers use any bandwidth left