USB is the Upper Sideband level of Single Sideband transmission of AM radio. It's more ore typically used and referred to in comparison to LSB.
The speed aspect of USB is one of its main selling points, so for your entertainment I present a quick summary of peripheral speeds (liberated from the FAQ at usb.org):
Introduction
In many of the more recent computers, little slot-like ports started to come included. Of course, the manual never said anything about the ports, and there were no devices back then with connectors that actually fit those slots. This slot is called a Universal Serial Bus (USB) port. Though this technology is fairly new, more and more manufacturers are beginning to sell USB-compatible peripherals and equipment. Almost 100 per cent of PC shipments are USB compatible, and the base of USB-installed PCs exceeds 500 million.
What the heck is USB?
USB stands for Universal Serial Bus. USB was developed by the computer industry leaders including Microsoft, Compaq, Intel, and NEC to increase the ease-of-use, performance and speed of peripherals by standardizing the way they attach to the PC. It is the easiest way to attach devices to your PC. The aim is on peripherals that connect to the outside of the computer. With USB, users won't have to open up the computer to install new peripherals. USB consists of a host, hub, and function. The host is the exchange point between USB peripherals, which is linked to a host controller, integrated into either the motherboard or PCI USB addon solutions. The hub allows multiple devices connect to the host. There is a USB hub already in USB-compatible compatible computers, that branches out to usually two connectors on the back of the computer. A function is a device that attached to the USB port.
So what? Why should I use USB?
What kind of peripherals can connect to USB?
There are thousands of USB peripherals on the market, from USB hubs, to scanners and printers, to digital video cameras. There are even USB modems and ISDN solutions on the market. Today, the USB logo appears all over the place, indicating peripherals that have USB support.
USB, the Universal Serial Bus, is designed to be able to connect practically any kind of peripheral to a PC. This makes it more versatile than any port which came before, but this versatility comes at a cost in terms of the complication of communicating with it. However, in practice much of this complication is hidden from the programmer; rather than needing to program drivers to communicate with the port directly, each operating system which supports USB provides a set of API calls for signalling to and from the port.
In addition to the raw API calls, both Linux and Windows (from Win 95 OSR 2.1 onwards) provide sets of ready-made class drivers, each designed to service a whole class of device. For example: Imaging Devices, such as cameras, scanners and so on; Audio Devices, like microphones and speakers; and Human Interface Devices, which include practically any peripheral which allows the user to interact with the machine: Keyboards, joysticks and mice, obviously, but also any number other devices which feature buttons, sliders or switches of any sort (including many devices which also fall into one or more of the other categories). The HID class is very powerful, but it only supports USB's low-speed data transfer rate of 1.5Mb/s. The faster rate of 12Mb/s is needed by peripherals which transfers significant amounts of audiovisual data, while the extra-fast rate of 480Mb/s introduced with USB 2.0 will allow pretty good quality real-time video to be input or output.
USB uses a multi-layered architecture for drivers, which means that rather than one driver providing for the whole range of communication between PC and peripheral there will typically be two or more drivers (usually at least four for USB) involved in communicating with any one peripheral. This approach is superficially more complex than having a single driver per peripheral, but in fact it makes things simpler for people writing or using drivers because it avoids unnecessary duplication of code; common functionality (such as communicating with the USB hub) can be handled by shared drivers.
Windows divides drivers into two types: Device drivers and bus drivers. Device drivers handle tasks which are specific to a single device or class of devices, while bus drivers handle tasks associated more generally with a bus. An application using a peripheral may communicate with one or more device drivers (in many cases, the two HID drivers plus one of the other class drivers). The device driver(s) in turn sends data down through three separate bus drivers. The first of these is the Hub Driver, which initialises ports and manages interactions between the device drivers and the next bus driver: The USB Bus-Class Driver. This is in charge of enumeration, power and general USB transactions, and intermediates between the Hub Driver and the final bus driver, the Host Controller Driver. This communicates directly with the hardware.
From Windows 98 on, drivers in Windows generally fit into a common framework called the WDM, the Win32 Device Model (before this Windows NT and Windows 95 used quite different driver models, forcing people to write separate drivers in order to support both OSs; Win 98 continues to support older drivers). Communication between drivers in Windows is achieved by means of Interrupt Request Packets (IRPs).
USB supports four distinct types of transfer:
References
Node your homework
printable version chaos
Everything2 Help
