Everything you wanted to know about USB
What is USB:
Universal Serial Bus (USB) is a
serial bus standard to
interface devices to a host computer.
What is USB for:
USB can connect computer peripherals such as mouse, keyboards,
PDA/s, gamepads and joysticks, scanners, digital cameras, printers, personal
media players, and flash drives.
Yeah, that means nothing to me:
USB was designed to
allow many peripherals to be connected using a single standardized interface
socket and to improve the
plug-and-play capabilities by allowing hot swapping, that is, by
allowing devices to be connected and disconnected without
rebooting the computer or
turning off the device.
The goal of USB is to end all of
these headaches. The Universal Serial Bus gives you a single, standardized,
easy-to-use way to connect up to 127 devices to a computer.
Just about every peripheral made now comes in a USB version.
Do I need it:
Yes, and whether you want it or not, you got it. (If your
computer was built in the last 5 years or so)
USB convenience and ease
of use, with simple Plug and Play
Hot Swappable (Installs
and uninstalls automatically)
Bus powered so it
doesn't require an external power supply (There are a few exceptions)
USB devises work
regardless of the operating system
USB implements connections to
storage devices using a set of standards called the USB mass storage device
class (referred to as MSC or UMS). This was initially intended for
traditional magnetic and optical drives, but has been extended to support a wide
variety of devices, particularly flash drives.
Human-interface devices (HIDs):
Mice and keyboards are frequently
fitted with USB connectors, but because most PC motherboards still retain PS/2
connectors for the keyboard and mouse as of 2007, they are often supplied with a
small USB-to-PS/2 adaptor, allowing usage with either USB or PS/2 interface.
Just about every peripheral made now comes in a USB version. A sample list of
USB devices that you can buy today includes:
- Flight yokes
- Digital cameras
- Scientific data acquisition devices
- Video phones
- Storage devices such as Zip drives
- Network connections
The Full Speed rate of
12 Mbit/s (1.5 MB/s) is the basic USB data rate defined by USB 1.0. All USB
hubs support Full Speed.
A Low Speed rate of
1.5 Mbit/s (187.5 kB/s) is also defined by USB 1.0. It is very similar to
full speed operation except that each bit takes 8 times as long to transmit.
It is intended primarily to save cost in low-bandwidth Human Interface
Devices (HID) such as keyboards, mice, and joysticks.
A High-Speed (USB 2.0)
rate of 480 Mbit/s (60 MB/s) was introduced in USB 2.0. All high-speed
devices are capable of falling back to full-speed operation if necessary.
Experimental data rate:
A Super-Speed (USB 3.0)
rate of 4.8 Gbit/s (600 MB/s). The USB 3.0 specification was released by
Intel and its partners in August 2008, according to early reports from CNET
news. According to Intel, bus speeds will be 10 times faster than USB 2.0
due to the inclusion of a fiber-optic link that works with traditional
copper connectors. Products using the 3.0 specification are likely to arrive
in 2009 or 2010.
USB communication takes the form
of packets. Initially, all packets are sent from the host, via zero or more
hubs, to devices. Some of those packets direct a device to send some packets in
USB connector properties:
- It is difficult to incorrectly attach a USB connector. Connectors cannot
be plugged-in upside down, and it is clear from the appearance and
kinesthetic sensation of making a connection when the plug and socket are
correctly mated. However, it is not obvious at a glance to the inexperienced
user (or to a user without sight of the installation) which way around the
connector goes, so it is often necessary to try both ways. More often than
not, however, the side of the connector with the "trident" logo should be on
- Only a moderate insertion/removal force is needed (by specification).
USB cables and small USB devices are held in place by the gripping force
from the receptacle (without the need for the screws, clips, or thumbturns
that other connectors require). The force needed to make or break a
connection is modest, allowing connections to be made in awkward
circumstances or by those with motor disabilities.
Types of USB connector:
Micro: The Micro-USB connector, was
announced by the USB-IF on January 4, 2007. It is intended to replace the
Mini-USB plugs used in many new smart phones and Personal digital assistants.
Type A: The Standard-A type of USB
connectors takes on the appearance of flattened rectangles that plugs into
downstream-port sockets on the USB host or a hub. This kind of connector is most
frequently seen on cables that are permanently attached to a device, such as one
on a cable that connects a keyboard or mouse to the computer. "A"
connectors head "upstream" toward the computer.
Type B: Standard-B connectors looks square
with beveled corners, and plugs into upstream sockets on devices and hubs. The
Standard-B connector is mainly used only for the device end of a removable
cable, such as between a hub and a printer. "B"
connectors head "downstream" and connect to individual devices.
Mini: The non-standard Mini-USB's, official
Mini-B, Micro-A, and Micro-B connectors are used for smaller devices such as
PDAs, mobile phones or digital cameras.
Extension Cable: Do you need to extend the distance from your computer to a USB
device such as a printer or scanner? According to the USB specification, you can
use passive extension cables (i.e., cables without an active repeater chip in
them) for distances up to 16 feet.
Maximum Useful Signaling Distance:
Although a single cable is
limited to 5 meters, the USB specification permits up to five USB hubs in a long
chain of cables and hubs. This allows for a maximum signaling distance of 30
meters, using six 5-meter cables and five hubs. In actual use, the last hub is a
more convenient endpoint since some USB devices include built-in cables intended
to directly connect to a hub, setting the maximum useful signaling distance at
Wireless USB is
based on the WiMedia Alliance's Ultra-WideBand (UWB) common radio platform,
which is capable of sending 480 Mbit/s at distances up to 3 meters and 110
Mbit/s at up to 10 meters. It was designed to operate in the 3.1 to 10.6 GHz
frequency range, although local regulatory policies may restrict the legal
operating range for any given country.
Most computers that you buy today
come with one or two USB sockets. With so many USB devices on the market today,
you easily run out of sockets very quickly. For example, I have a USB printer, a
USB scanner, a USB Webcam and a USB network connection. My computer has only one
USB connector on it, so the obvious question is, "How do you hook up all the
The easy solution to the problem is
to buy an inexpensive USB hub. The USB standard supports up to
127 devices, and USB hubs are a part of the standard. A hub typically has four
new ports, but may have many more. You plug the hub into your computer, and then
plug your devices (or other hubs) into the hub. By chaining hubs together, you
can build up dozens of available USB ports on a single computer.
The Universal Serial Bus has the following features:
- The computer acts as the host.
- Up to 127 devices can connect to the host, either
directly or by way of USB hubs.
- Individual USB cables can run as long as 5 meters; with hubs, devices
can be up to 30 meters (six cables' worth) away from the host.
- With USB 2.,the bus has a maximum data rate of 480 megabits per
- A USB cable has two wires for power (+5 volts and ground) and a twisted
pair of wires to carry the data.
- On the power wires, the computer can supply up to 500 milliamps of power
at 5 volts.
- Low-power devices (such as mice) can draw their power directly from the
bus. High-power devices (such as printers) have their own power supplies and
draw minimal power from the bus. Some Hubs can have their own
power supplies to provide power to devices connected to the hub.
- USB devices are hot-swappable, meaning you can plug
them into the bus and unplug them any time. (Starting with SP-2)
- Many USB devices can be put to sleep by the host
computer when the computer enters a power-saving mode.
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