This is a simple USB to 4 port RS232 converter board. Modern PCs (cheap ones anyway) generally don't have RS232 ports anymore. I am working on a data acquisition system that will require multiple RS232 ports to talk to different instruments. One of the problems with USB is that you can't guarantee that every time the system boots, the USB components will enumerate to the same devices. It would be possible to use multiple, single port USB to RS232 adapters to connect to the instruments, except that each time the system reboots, the instruments could appear on different TTYs. Using a single USB device with 4 UARTs in it insures that ttyUSB0 connects to the same physical device every boot cycle.