 Gordon Bell of DEC designed the first UART, occupying an entire circuit board called a "line unit", for the PDP series of computers beginning with the PDP-1.According to Bell, the main innovation of the UART was its use of sampling to convert the signal into the digital domain, allowing more reliable timing than previous circuits that used analog timing devices with manually adjusted potentiometers.To reduce the cost of wiring, backplane and other components, these computers also pioneered flow control using XON and XOFF characters rather than hardware wires.