The Advantages of USB Ports Over Parallel Portsby Gareth Downes-Powell
In the past, the main method of interfacing with a PC was through the PC's serial or parallel ports, with limited data transfer rates and only one or two sockets available for connecting devices. Designed as a replacement, the Universal Serial Bus system allowed you to connect multiple devices at once, using fast data transfers through a universal interface. During the transition period, many motherboards offered parallel and USB ports, with the parallel interface eventually deprecated as USB devices replaced parallel devices in use.
Although faster than serial ports, PC parallel ports have a data transfer rate of 150kB/s, increased to 2MB/s in EPP and ECP modes. In comparison, USB v1.1 has a data transfer rate of 12Mbit/s increased to 480Mbit/s with the USB 2.0 specification. USB 3.0 increases the speed further, allowing data rates of up to 5Gbit/s. This bandwidth increase boosts the speed of data-intensive operations such as scanning, and makes possible the use of high-speed audio and video devices.
The PC parallel port can only provide power for signalling and data transfer, meaning that peripherals require their own external power supply for powering the peripheral itself. USB improves on this by providing up to 500mA to power the peripheral, increasing to 900mA with USB 3.0. Although high power peripherals such as printers still require their own external supply, many smaller peripherals such as webcams or flash drives receive all their power directly from the USB port. This also allows you to charge the batteries of mobile devices such as phones or MP3 players directly from the USB port.
Ease Of Use
Diagnosing problems with parallel devices could be a difficult task, with a number of different parallel port standards such as SPP, ECP and ECP, which you had to set up in the computer's BIOS. USB supports plug and play, making it far simpler to connect devices and get them up and running. When you plug in a device to a USB port, the device's vendor ID and product ID are sent to the computer, allowing it to determine the correct driver for the device. If the driver is not already present, the computer can prompt you for the correct driver by name, or download the driver automatically over the Internet in many cases.
Most PCs only had one parallel port available, which led to devices such as printers and scanners being daisy chained together, allowing both to be connected at once. This caused further incompatibility problems between different hardware manufacturers, and made it harder to get devices to function correctly. Designed for expansion, the USB system allows up to 127 devices to run from a single controller. Although most PCs have between four and eight USB ports on the motherboard, you can use USB hubs to add more sockets as needed, allowing multiple devices to be connected and available for use at the same time.