About Transmissions - Multi-speed Rear Axles

I am curious about something. I know that in the past trucks used multi (2 or 4) speed rear axles to achieve multiple speeds forward. But I read now that multi-speed differentials have pretty much disappeared. So, how do modern-day trucks implement 9, 10, 13, 15 or 18-speed transmissions if not with a multi-speed differential, and what, exactly, does the Range Selector on such trucks (with manual transmissions) do?

Range selectors/splitters, do just that split the gears, from low to high range and back again...... 1st thru 5th low, splitter up, high range 6th thru 10th etc (all in the trans, not the Diff's)

Range selectors/splitters, do just that split the gears, from low to high range and back again...... 1st thru 5th low, splitter up, high range 6th thru 10th etc (all in the trans, not the Diff's)

I know what Low and High Range is. My question was, how is this accomplished if not by a multi-speed differential? Does the transmission itself contain two sets of gears which are selected by means of the Range and High/Low Selectors? How does the transmission "know" which gear is being "requested" via the shift lever and Range Selectors?

Steven E. Are you still technical support for your company or are you a driver now?

(all in the trans, not the Diff's)

<------ told ya lol