What this 74HC multiplexer does
The Texas Instruments SN74HC258N is a 4 x 2:1 multiplexer from the 74HC family. It selects one of two 4-bit data sources onto a single 4-bit output bus, controlled by a common select line. This is a through-hole 16-DIP part, so it fits legacy sockets, breadboards, or boards where a surface-mount footprint isn't practical. Supply range is 2V to 6V, which means it works on both 3.3V and 5V rails without a level translator. Output drive is symmetric at 7.8mA per channel for both high and low states. That's enough to drive a few CMOS gate inputs or a low-power LED, but not a heavy bus — plan a buffer if you're driving a long trace or multiple loads.
It remains a standard catalog item in the 74HC logic family, and the through-hole DIP package keeps it accessible for repair, retrofit, and low-volume production runs.