Universal Serial Buses, or USB, are one of the greatest things that have been introduced to the PC market. They are ports that allow you to connect up to 127 peripherals to your computer, and they are slowly replacing previous connecting devices like serial and parallel ports. Here's a list to give you an idea of what types of devices you can connect to your computer via a USB port: you can connect mice, keyboards, printers, scanners, modems, storage devices, digital cameras, and speakers- just to name a few!
Universal Serial Buses have host controllers in the motherboard of the computer. To connect to additional devices, there are USB ports located on the rear panel of the computer. Almost all modern personal computers have one or two USB connectors on their back panels. Most USB devices have their own cables, and all you need to do is connect the device cables to the USB connector at the back of your computer!
There are two types of connecting cables: cables with an "A" connection and cables with a "B" connection. These two types of cables are merely used to avoid confusions. "A" connections are used for devices that want to send data to the computer, while "B" connections send data from the computer to the device. All USB cables actually have four wires. Two wires are used to get power, while the other two wires are twisted about each other and are used to carry data.
Now, if PCs only have one or two USB connectors, how, you might ask, can you connect 127 peripherals to your computer? Well, this is possible because of devices called USB hubs. USB hubs can be connected via one of the USB connectors on the back panel of your computer. These hubs let you connect an additional four USB devices to your computer. If you set up a string of USB hubs, you can connect dozens of additional devices!
There are two different types of USB devices. They are grouped according to if they have their own power supply or not. Those without their own power supply are usually devices like mice and keyboards, which normally do not require a lot of power anyhow. These devices usually get power from the computer. However, if you have dozens of devices that depend on the computer for power, the computer will not be able to keep up with all the demands. This is why sometimes USB hubs can be powered to supply power to these devices. Other devices, like printers, have their own power supply. These present no problems to the computer because they don't depend on the computer system for power.
USB ports can transfer data at up to 12 megabits per second. These ports can perform three different types of data transfer.
2. Bulk Transfers
3. Isochronous Transfers
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