The “W” signifies that the board includes wireless. Interestingly, the wireless chip is an Infineon CYW43439) which is itself a microcontroller running its own ARM Cortex chip (M3). The Pico’s USB device includes another ARM microcontroller. So, with the dual Cortex (or Hazard) chips that are user programmable, and the 8 PIOs, these devices really pack a punch.

As a result of adding the wireless (microcontroller) chip to the Pico, the Pico W’s on-board LED is accessible only through the CYW43439. Yeah, weird but it makes for an interesting solution.