 The original 8250 UART chip shipped with the IBM personal computer had a one character buffer for the receiver and the transmitter each, which meant that communications software performed poorly at speeds above 9600 bit/s, especially if operating under a multitasking system or if handling interrupts from disk controllers.High-speed modems used UARTs that were compatible with the original chip but which included additional FIFO buffers, giving software additional time to respond to incoming data.A look at the performance requirements at high bit rates shows why the 16-, 32-, 64- or 128-byte FIFO is a necessity.