by- vishal sharma
USB runs at up to 12Mbit/second; that's 12,000,000 bps (bits per second). Traditional serial ports mostly run at up to 115200 bps and even then can be subject to data loss due uto UART overflows and missed interrupts. USB has none of those problems - speed is reliable and high.
A USB port can run many devices at once, up to 128 in total. To add more devices to a single port, a low cost hub (splitter) can be used. Hubs are often built into monitors. The great advantage is that you no longer have to worry about having enough ports for new perhipherals or use ports for purposes for which they weren't inteded (e.g. external tape drives on parallel ports !).
USB provides power to the periperhal you connect, so there is no need for an external mains PSU for most products.
4.Truly Plug & Play
USB devices confogire themselves; your PC will automatically detect the new device and install the software for it.
USB devices can also be hot-swapped - i.e. connected or removed while the PC is switched on.