In the diagram, a start bit is sent, followed by eight data bits, no parity bit and one stop bit, for a 10-bit character frame. The number of data and formatting bits, and the transmission speed, must be pre-agreed by the communicating parties.
After the stop bit, the line may remain idle indefinitely, or another character may immediately be started.
The minimum stop bit length required by the system can be larger than a "bit". In fact, old electromechanical teletypewriters could demand 2 stop bits to allow mechanical impression without buffering, and RTTY amateur radio is known to historically require 1.5 stop bits. New hardware that doesn't support fractional stop bits can be configured to send 2 stop bits when transmitting and requiring 1 stop bit when receiving.
Very early experimental printing telegraph devices used only a start bit and required manual adjustment of the receiver mechanism speed to reliably decode characters. Automatic synchronization was required to keep the transmitting and receiving units "in step". This was finally achieved by Howard Krum, (an electrical engineer and son of Charles Krum) who patented the start-stop method of synchronization , granted September 19, 1916 then , granted December 3, 1918. Shortly afterward a practical teleprinter was patented July 3, 1917.
Between computers, the most common configuration used was "8N1": eight bit characters, with one stop bit and no parity bit. Thus 10 Baud times are used to send a single character, which has the nice side-effect that dividing the signalling bit-rate by ten results in the overall transmission speed in characters per second.
Asynchronous start-stop is the physical layer used to connect computers to modems for many dial-up Internet access applications, using a data link framing protocol such as PPP to create packets made up out of asynchronous serial characters. The performance loss relative to synchronous access is negligible, as most modern modems will use a private synchronous protocol to send the data between themselves, and the asynchronous links at each end are operated faster than this data link, with flow control being used to throttle the data rate to prevent overrun.
See comparison of synchronous and asynchronous signalling for alternatives to asynchronous start/stop operation.