What Is USB ?
An Introduction to the Universal Serial Bus
USB (or Universal Serial Bus) is a 13-year old standard
that was originally designed to connect, then smart phones to PCs
in the mid-90s. It later became the de facto standard for
connecting any external, thanks to USB's built-in power supply and
relatively fast speeds. The then-unique one-cable approach sparked a
revolution that spawned everything USB (no, not this site) ranging
from flash drives, hard drives, speakers, TV tuners to webcams. All
these top at 12Mbps, at which speed is only good for mice and
keyboards; so the official USB body upgraded the specs to USB 2.0,
adding Hi-Speed USB mode operating at 480Mbps. As more applications
moved on to wireless thereafter, the same group decided to follow
the trend by cutting the wire in the latest Certified Wireless USB
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
Features of USB
One 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.
Operating 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
Three device speeds.
Low speed (1.5 Mbps) is mostly used for input devices such as mice
and keyboards, while Full speed (up to 12 Mbps) and High speed(USB
up to 480Mbps) is used mostly for
video/audio capture devices and storage devices.
Hot pluggable. Devices can be attached to and detached from the
computer without turning off the system. No jumper or IRQ settings
Plug-and-Play. Once the device is connected to the computer, the
system automatically recognizes the device connected and installs
the appropriate drivers.
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.
Point to point connection.
USB enables devices to be connected in any order, eliminating the
need for external terminators.
Bus-powered 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
- USB mice, USB keyboards, USB joysticks,USB trackballs, USB touchpads,
USB phones, video and USB still image cameras, USB PC card readers,
USB rc laser pointer,
Output devices - text and graphics printers,
card reader, USB gift,
Storage devices -
Communication devices -
keyboard hubs and
USB 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
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
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 USB.
The Development of USB 2.0
The companies that led the development of USB 2.0 had the
expertise needed to focus on a specification that supports higher
functionality peripherals. The USB 2.0 core team included 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 didn't intend
to charge royalties for essential patents required to implement the
USB 2.0 specification. Intel had released the EHCI
standard that will insure that all USB 2.0 devices are built to the
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 supports 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
Serial Bus (USB) 2.0 is an external serial interface used on
computers and other digital devices to transfer data using a USB
cable. The designation “2.0” refers to the standard or version of
the USB interface. As of fall 2006, USB 2.0 remains the current
USB is a
plug-and-play interface. This means that the
computer does not need to be powered off in order to plug in or
unplug a USB 2.0 component. For example, an
iPod or other
MP3 player can be connected to a computer via a USB cable
running to the USB 2.0 port. The computer will register the device
as another storage area and show any files it contains.
USB 2.0 interface, one can transfer files to or from the
MP3 player. When finished, simply unplug the USB cable from the
interface. Because the computer does not need to be shut down to
plug in the device, USB components are considered “hot swappable.”
MP3 players, many other external devices use USB 2.0 data ports,
including digital cameras, cell phones, and newer cable boxes.
Native components also make use of USB, such as mice, keyboards,
external hard drive enclosures, printers, scanners, fax machines,
wireless and wired networks keys, and
WiFi scanners. One of the most popular and convenient USB
gadgets is a memory stick.
standards change from an existing version to a newer version, as
they did from USB 1.1 to USB 2.0, hardware made for the newer
version is in most cases backwards-compatible. For instance, if a
computer has a USB 1.1 port, a device made for USB 2.0 that is
marked as “backwards compatible to USB 1.1” will work on the older
port. However, the device will only transfer data at 1.1 speeds
using a USB 1.1 port.
In breif, Currently,
computers are built with USB 2.0 ports. The USB 2.0 standard
encompasses three data transfer rates:
Low Speed: 1.5 megabits per
second, used mostly for keyboards and mice.
Full Speed: 12 megabits per
second, the USB 1.1 standard rate.
Hi Speed: 480 megabits per
second, the USB 2.0 standard rate.
Since USB 2.0 supports all three data rates, a device that is marked
as “USB 2.0 compliant” isn’t necessarily
It may operate through a USB 2.0 port at one of the slower speeds.
Look for clarification when shopping for hi-speed USB 2.0 devices.
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
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
disconnect devices without shutting down your computer allowing
flexibility and expandability.
Wireless USB Brings Greater Convenience and Mobility to Devices
Overview: Unwiring USB
Imagine if all the devices in a home office -- such as printer,
scanner, external hard drive, and digital camera -- could be
connected to your PC without any wires. Imagine if all the
components for an entire home entertainment center could be set up
and connected without a single wire. Imagine if digital pictures
could be transferred to a photo print kiosk for instant printing
without the need for a cable. These are just some of the possible
scenarios for high-speed wireless USB (WUSB) connectivity, the
latest technology developed to bring even greater convenience and
mobility to devices.
Universal serial bus (USB) technology has been a popular connection
type for PCs and it's migrating into consumer electronic (CE) and
mobile devices. Now this high-speed and effective connection
interface is unwiring to provide the functionality of wired USB
without the burden of cables. This next iteration of USB technology
is the focus of the new Wireless USB Promoter Group, which will
define the specifications that will eventually provide standards for
Wireless USB Promoter Group
At the Spring 2004 Intel Developer Forum, formation of the Wireless
USB Promoter Group was announced. The group is comprised of seven
industry leaders: Agere Systems, HP, Intel, Microsoft Corporation,
NEC, Philips Semiconductors and Samsung Electronics.
The Wireless USB Promoter Group is chartered with defining the
wireless USB (WUSB) specification. Already there has been some
progress with the definition of a WUSB specification with a targeted
bandwidth of 480 Mbps. This specification maintains the same usage
and architecture as wired USB with a high-speed host-to-device
connection. With these considerations in place, it will enable an
easy migration path for today's wired USB solutions.
Additionally, WUSB specifications will be based on ultra wideband
(UWB) radio efforts by the MultiBand OFDM Alliance (MBOA) and
WiMedia Alliance, both open industry associations that promote
personal-area range wireless connectivity and interoperability8among
multimedia devices in a networked environment.
The fundamental relationship in WUSB is a hub and spoke topology, as
shown in Figure 1. In this topology, the host initiates all
the data traffic among the devices connected to it, allotting time
slots and data bandwidth to each device connected. These
relationships are referred to as clusters. The connections are
point-to-point and directed between the WUSB host and WUSB device.
Figure 1 -- WUSB topology
The WUSB host can logically connect to a maximum of 127 WUSB
devices, considered an informal WUSB cluster. WUSB clusters coexist
within an overlapping spatial environment with minimum interference,
thus allowing a number of other WUSB clusters to be present within
the same radio cell.
Topology will support a dual role model where a device can also
support limited host capabilities. This model allows mobile devices
to access services with a central host supporting the services
(i.e., printers and viewers). This model also allows a device to
access data outside an existing cluster it may currently be
connected to by creating a second cluster as a limited host.
Additionally, high spatial capacity in small areas is needed to
enable multiple device access to high bandwidth concurrently.
Multiple channel activities may take place within a given area. The
topology will support multiple clusters in the same area. The number
of clusters to be supported is still being determined.
There are several architectural considerations in developing WUSB.
In addition to providing wireless connectivity, WUSB must be
backwards compatible with wired USB and provide a bridge to wired
USB devices. Also, the host and solutions will need to enable the
exchange of data between clusters or devices not related to the same
Low-cost implementation of WUSB will also be important to the
successful integration of the technology. Implementation will follow
the wired USB connectivity models as closely as possible to reduce
development time and to preserve the low-cost, easy-to-use model,
which has become pervasive in the PC industry.
WUSB performance at launch will provide adequate bandwidth to meet
the requirements of a typical user experience with wired
connections. The 480 Mbps initial target bandwidth of WUSB is
comparable to the current wired USB 2.0 standard. With 480 Mbps
being the initial target, WUSB specifications will allow for
generation steps of data throughput as the ultra wideband radio
evolves and with future process technologies, exceeding limits of 1
The specification is intended for WUSB to operate as a wire
replacement with targeted usage models for cluster connectivity to
the host and device-to-device connectivity at less than 10 meters.
The interface will support quality delivery of rich digital
multimedia formats, including audio and video, and will be capable
of high rate streaming (isochronous transfers).
A new class of devices, called WUSB dual-role devices, will give
rise to usage scenarios not previously possible. These devices will
offer both limited host and device capabilities similar to USB
With the growing use of digital media in the PC, consumer electronic
(CE) and mobile communication environments, a common standard
interconnect is needed to support the on-going convergence of these
environments. The trend toward convenient wireless distribution of
digital information provides an opportunity to introduce a single,
standard wireless interconnect capable of supporting usage models
across all three environments.
The CE environment will have high-performance wireless interface
expectations. Consumer usage models (Figure 2) will center on
streaming media distribution that typically uses compression
algorithms. The performance objective is to ensure a high quality of
service is maintained to meet typical consumer entertainment
Figure 2 -- Consumer Usage Models
Typical video delivery with standard SDTV/DVD will consume between 3
and 7 Mbps while HDTV will use between 19 and 24 Mbps. A point
distribution technology like wireless USB with an effective
bandwidth of 480 Mbps could manage multiple HDTV streams. Host
buffering could enable a network backbone to effectively distribute
content to all distribution hosts, enhancing the quality experience
for all users.
Business applications for WUSB include a variety of different usage
possibilities. Common devices such as printers, scanners, hard
drives, and projectors could all be used in wireless scenarios.
These devices would function the same way as if they were using
wired USB, but without all the cables. Office services on the
corporate network could migrate to WUSB and benefit from faster
performance than shared network devices offer.
Security and Device Association
WUSB security will ensure the same level of security as wired USB.
Connection-level security between devices will ensure that the
appropriate device is associated and authenticated before operation
of the device is permitted. Higher levels of security involving
encryption should be implemented at the application level.
Processing overhead supporting security should not impose noticeable
performance impacts or add device costs.
One of the primary objectives when implementing a wireless
interconnect is that it is easy to install and use. Wired
connections provide the user with implied expectations, that is that
the device is connected as specified by the user when they install
the wire. When the wire is installed, the user has basic
expectations and when these expectations do not take place (plug
does not fit), there is a known recourse.
Wireless connections, on the other hand, due to environmental
characteristics, may establish connection paths that are not
obvious. In fact, it may not be obvious when a device is connected.
So WUSB devices installed for the first time should automatically
install drivers, security features, and so on and associate with
systems that they can interact with. The concepts of 'turn on and
use it' with an easy setup procedure will be employed.
WUSB in the Future
The first Wireless USB implementations will likely be in the form of
discrete silicon that will be introduced in a number of form
factors. These may include add-in cards and dongles along with
embedded solutions to support the technology's introduction and
subsequent rapid ramp up.
But the wireless future will arrive once WUSB, along with the common
ultra wideband platform, becomes a standard part of every processor
and chipset and is integrated in CMOS silicon.
As the latest iteration of USB technology, wireless USB (WUSB) will
offer the same functionality as standard wired USB devices but
without the cabling. As the new Wireless USB Promoter Group prepares
to develop the specifications that will help standardize the
technology, the industry is planning products that can take
advantage of the convenience and mobility that this new device
interconnect will offer.