Basic register, may be any number of bits.
Typically called a flip-flop if one bit.
The system clock is always running from power on
to power off.
1 +-------+ +-------+ +------
clk | | | | |
0 --+ +-------+ +-------+
^ ^ ^ ^ ^
| | | | |
raising falling input | input
edge edge open | closed
|
| new output avaiable
+----------+ input
| | v
| register | +------------+
input ->| |-> output | |
data | | data | register |
| | | |
| | +------------+
+----------+ v
^ output
|
|
clk not usually shown on schematics