Developer Guide
FPGA Optimization Guide for Intel® oneAPI Toolkits
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Visible to Intel only — GUID: GUID-82B5929D-948F-4581-9C63-15BA70F8C707
Register
A register is the most basic storage element in an FPGA. It has an input (in), an output (out), and a clock signal (clk). It is synchronous, that is, it synchronizes output changes to a clock. In an ALM, a register may store the output of the LUT.
The following figure illustrates a register:

The clock signal is implied and not shown in some figures.
The following figure illustrates the waveform of register signals:

The input data propagates to the output on every clock cycle. The output remains unchanged between clock cycles.