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

Geeky stuff:

USB mass-storage:  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:

USB signaling: 

Experimental data rate:

USB packets:  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 reply.

USB connector properties:

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 25 meters.

Wireless USB: 

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.

USB Hubs:  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 devices?"

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.


USB Features: 

The Universal Serial Bus has the following features:




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