Difference between TI LM2587S-12/NOPB and LM2587SX-12/NOPB


What does the added X in the part number LM2587SX-12/NOPB Mean? Does it change the part?

The X is a packaging code, and calls out Tape & Reel packaging.
Without the X, like LM2587S-12/NOPB, the part will be in Tube packaging.

Both part numbers will be the exact same parts, so they will function the same.