Universal Serial Bus (USB) makes connecting devices to your
computer faster, easier and virtually limitless. High-speed USB devices are
capable of communicating at speeds up to 12 megabits per second. USB makes
Plug-and-Play a reality. Simply plug a USB device to your computer- without
shutting down and without having to open your computer. Connect up to 127
printers, modems, keyboards, mice, joysticks, scanners, digital cameras, and
other USB devices.
The growth of USB products and related services over the next years
will be outstanding. USB will soon replace legacy devices, and with most PCs and
notebooks shipping with USB ports as well as major operating systems supporting
USB, the technology is maturing and gaining momentum. Universal Serial Bus is
now the dominant interface for connecting virtually all computer peripherals -
printers, scanners, modems, cameras and virtually any other form of
Universal Serial Bus
USB, or Universal Serial Bus, is a peripheral bus connectivity
standard which was conceived, developed and is supported by a group of leading
companies in the computer and telecommunication industries - Compaq, DEC, IBM,
Intel, Microsoft, NEC, and Northern Telecom. USB was developed with one goal in
mind: to make it easier for users to plug-and-play computer peripherals without
having to open the box, install cards into dedicated computer slots and
reconfiguring the system. The current standard published and implemented on most
USB devices is version 1.1.
USB makes it convenient to simultaneously use and connect up to 127
peripherals to a computer without using several connectors, different interrupts
and IO addresses. The computer automatically recognizes the device connected and
installs the appropriate drivers. It enables computer users to
"hot-plug" computer peripherals to their PCs and start using them
without having to reboot.
Features of USB
type of device cable. USB also standardizes connectors and cables. USB
cables have two connectors: an A connector and a B connector. The A
connector is the end that goes into the computer, and the B connector goes
into the device. The total cable length between devices must not exceed 5
meters, or 16 feet.
System support. USB driver support is built into the latest
versions of the Windows and Apple operating systems. It is not compatible
with all operating systems. Some USB devices will work with Windows 95 OSR
2.1, but Windows 98, Windows 2000, MAC OS 8.1 or higher offer much more USB
device speeds. Low speed (1.5 Mbps) is mostly used for input
devices such as mice and keyboards, while high speed (up to 12 Mbps) is used
mostly for video/audio capture devices and storage devices.
pluggable. Devices can be attached to and detached from the
computer without turning off the system. No jumper or IRQ settings are
Once the device is connected to the computer, the system automatically
recognizes the device connected and installs the appropriate drivers.
peripherals. USB makes it possible to simultaneously use and
connect up to 127 devices to a single bus. The computer typically has 2 USB
ports, so USB hubs are used to connect additional devices to the computer.
USB hubs have multiple USB ports for connection of USB devices and for daisy
chaining one or more hubs.
to point connection. USB enables devices to be connected in any
order, eliminating the need for external terminators.
and self-powered. USB supports both bus-powered and self-powered
devices. Good examples of bus-powered and self-powered devices are USB hubs.
USB hubs can draw power either from the host device (bus-powered) or from an
external AC power supply (self-powered). Each downstream port on a
bus-powered hub typically supplies up to 100 mA. On the other hand, each
downstream port on a self-powered hub typically supplies up to 500mA.
USB devices can be connected to the computer either directly
through the USB port on the back of the computer or through a USB hub. The
Universal Serial Bus connects USB devices with the USB host. There is only one
host on any USB system. The USB interface to the host computer system is
referred to as the host controller.
The host PC and USB hub each contain a USB controller. This
controller is typically mounted on the PC motherboard, on a PCI add-in card or
on the hub itself. The controller's function is to manage the USB devices on the
serial bus and to help reduce the load on the computer CPU.
USB devices may be attached or detached from the USB host or hub.
They may obtain power from an external source and/or from USB through the hub to
which they are attached. When a USB device is attached to or removed from the
USB hub, the host uses a process known as bus enumeration to identify and manage
the device state changes necessary. A USB device must be configured and the host
PC is responsible for configuring a USB device. The host typically requests
configuration information from the USB device to determine the device's
capabilities. This makes it possible for users to plug-and-play their USB
devices to the PC.
Human Interface devices - mice, keyboards, joysticks, trackballs,
touchpads, gamepads, microphones, video and still image cameras, PC card
readers, and scanners
Output devices - text and graphics printers, photo printers and speakers
Storage devices - floppy drives, hard drives, Zip drives Communication
devices - infrared devices, ISDN devices, networking equipment and modems
Hubs - standalone, keyboard hubs and monitor hubs.
USB currently supports a data transfer rate of
12 megabits per second. USB 2.0 is a lot faster, 40x faster to be precise. USB 2.0 produces data transfer rates, up to 480 Mbps. Compaq, Hewlett-Packard, Intel,
Lucent, Microsoft, NEC, and Philips jointly led this initiative, which
enables new classes of high-performance peripherals.
The higher bandwidth of USB 2.0 allows high-performance
peripherals, such as scanners, video conferencing cameras, next-generation
printers, and faster storage devices to be easily connected to the computer via
USB. The higher data rate of USB 2.0 opens up the probability of new
and exciting peripherals. With the increased availability of USB-enabled PCs and
USB peripherals on the market today, the need for legacy dependent input/output
(I/O) connectivity is decreasing significantly. USB 2.0 is a significant
step towards providing additional I/O bandwidth and broadening the range of
peripherals that may be attached to the PC.
USB 2.0 is both forward and backward compatible with
USB 1.1. Existing USB peripherals will operate with no change in a USB 2.0
system. Devices, such as mice, keyboards and game pads, will not require the
additional performance that USB 2.0 offers and will operate as USB 1.1 devices.
All USB devices co-exist in a USB 2.0 system. The higher speed
of USB 2.0 greatly broadens the range of peripherals that may be attached to
the PC. This increased performance also allows a greater number of USB
devices to share the available bus bandwidth, up to the architectural limits of
Leading the Development of USB 2.0
The companies that are leading the development of USB 2.0 have the
expertise needed to focus on a specification that supports higher functionality
peripherals. The USB 2.0 core team includes all four members of the USB 1.1 core
team (Compaq, Intel, Microsoft, and NEC), and three new members (Hewlett
Packard, Lucent and Philips). As with USB 1.1, members of the core promoters
group do not intend to charge royalties for essential patents required to
implement the USB 2.0 specification. Intel has recently released the EHCI
standard that will insure that all USB 2.0 devices are built to the same
I/O connectivity is being further advanced with the IEEE 1394
standard. USB 2.0 and 1394 primarily differ in terms of application focus. USB
2.0 will support the full range of popular PC peripherals while 1394 targets
connection to audio visual consumer electronic devices such as digital
camcorders, digital VCRs and digital televisions.
IEEE 1394 - Similar but not the same
IEEE-1394 technology, also known as FireWire® or iLink™ is a
high-performance and low-cost digital interface that merges computing
electronics into consumer multimedia. It is perfect for high-end users requiring
data intensive applications for storage drives, high-quality digital video and
audio. With FireWire, you can connect up to 63 devices in one chain and support
speeds of up to 400 Mbps, 10 times faster and 9 times as many devices per chain
than SCSI. It's plug-and-play and hot-swappable: you can connect and disconnect
devices without shutting down your computer allowing flexibility and
Is USB? and parts of the
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