Shift registers can have both parallel and serial inputs and outputs. These are often configured as "serial-in, parallel-out" (SIPO) or as "parallel-in, serial-out" (PISO). There are also types that have both serial and parallel input and types with serial and parallel output. There are also "bidirectional" shift registers which allow shifting in both directions: L→R or R→L. The serial input and last output of a shift register can also be connected to create a "circular shift register". A PIPO register (parallel in, parallel out) is very fast – an output is given within a single clock pulse.