The next concept fully based on UART so read this,
UART is Pronounced as u-art, and short for universal asynchronous receiver-transmitter, the UART is a computer component that handles asynchronous serial communication. Every computer contains a UART to manage the serial ports, and some internal modems have their own UART.
As modems have become increasingly fast, the UART has come under greater scrutiny as the cause of transmission bottlenecks. If you are purchasing a fast external modem, make sure that the computer’s UART can handle the modem’s maximum transmission rate. The newer 16550 UART contains a 16-byte buffer, enabling it to support higher transmission rates than the older 8250 UART.