The firmware on today's USB drives is flashable from Windows (usually XP) using the manufacturer's proprietary utility for that particular flash memory controller. Sandisk remains mysterious as their utility if it exists has not been leaked.

This is likely because the firmware has not been perfected yet, so ugrades are continuing. Plus completely different characteristics can be obtained to arrive at multiple device brands or behaviors from the same hardware. "Identical" flash drives from the same manufacturer containing the same exact chips can often have different firmware revisions, and different resulting performance.

On most units an additional CDROM device, or extra partitions (hidden, private/secure or not) can be configured to be detected (or not) when plugged in to any OS. The controller provisions the available flash memory among the dictated devices and makes them available to you.

I've been adjusting the firmware for a couple years now as I do the continuous improvement on my rapid multibootable sticks.