Universal Serial Ports or USBs have become extremely common and are found on most modern computers. Not only do these allow the users to attach other external devices to the computer, but also the operating systems support it, hence making installations easier. The development of USB came at a time when connecting external devices such as printers and modems required a separate specific parallel port. These were not even fast and required a lot of work during installations. However, with the invention of USB, it gave the users an easy and standardized way to connect up to 127 devices to any computer! Beginning from printers, scanners, mouse, joysticks, flight yokes and digital cameras to webcams, modems, speakers, telephones, video phones, scientific data acquisition devices and network connections – USB has offered a single solution to them all!
The USB Port
For those wondering how to connect a USB device to the computer, it is quite simple, really!
- Simply find the USB port on the computer and connect the USB connector with it. Typically, you will find a USB socket, rectangular in shape, at the back of your computer.
- If it is the first time you are connecting a USB device to computer, it will be automatically detected by the operating system and the driver disk will be asked for by the system.
- However, if you have already installed the USB device, the computer will automatically begin its communication with the device. This connection can then be connected or terminated at any point of time.
These days, the USB devices come with their own built-in cable. Usually the cable has an “A” marked for the connection. If this does not exist, then the device will showcase a socket that is meant for accepting a “B” USB connector. “A” and “B” are described for specific functions – A connects “upstream” i.e. towards computers, and B connect “downstream” towards the individual devices.
How it works!
When the host is turned on, it detects all the devices connected to it through USB and assigns each device with a unique address. This is called the process of enumeration. This process occurs again once the devices are connected to the bus. Then the host seeks information from each device with regards to the kind of data transfer desired– interrupt, bulk or isochronous:
- Interrupt mode is usually chosen by small devices requiring very little data sending.
- Bulk mode is used by devices which require bulk data transfer. For example, a Printer.
- Isochronous mode is chosen by the devices looking for streaming (speakers for example).
The host can also control packets in terms of commands and query parameters.
Once the devices are enumerated, the host keeps track of the total bandwidth requirements of the isochronous and interrupt devices. The maximum they are allowed to consume is 90 percent of the 480 Mbps bandwidth. However, once the limit is reached, the host denies all further access. The rest 10 percent bandwidth is used by the bulk packets and control packets.