Turbo was the default behavior. There was a toggle button that turned off the turbo light and slowed the machine down when needed for compatibility. Note: almost nobody needed this capability it sometimes they bumped the button and later wondered why the pc was slow.

Reminds me of why NASA had to rename the thing that went over astronaut's private part to large, gigantic, and humongous because nobody woud pick small and normal.

The previous user isn't wrong per se, but just to clarify: if the indicator light is on, the "turbo" (default) mode is on and the device is running at full performance. Turbo off means it's downclocked.

It's more a misnomer to call it turbo when in fact it's just the standard speed of the device, while the mode that is actually toggled using the turbo button is what causes it to run slower for compatibility reasons.