This has a lot of information and answers regarding the function of the different 4WD operations in 100's.
https://forum.ih8mud.com/100-series-cruisers/787959-uzj100-4x4-4wd-system-explained.html
Some good stuff in that thread.
Is there a difference between 80 and 100 4 wheel drive system? What about other120 series full time like the 4runners that are full time?
Zack, I'll describe things as directly as I know how.
For the 100 series:
4Hi, CDL Unlocked - Full time ATRAC, Full time ABS. ATRAC engages gradually applying hydraulic pressure to the slipping wheel to gradually transfer power. Eliminates the possibility of the "one wheel peel," but does so gracefully.
4Lo, CDL Unlocked, Full time ATRAC, Full time ABS, ATRAC engages suddenly, providing instant hydraulic force to the slipping wheel to immediately transfer power.
4Lo or 4Hi, CDL Locked, Same ATRAC / ABS performance (instant for Lo, gradual for Hi), but on a "per axle" basis. ATRAC is only concerned with slippage DS to PS, and not F/R, since the CDL is splitting power 50/50 F/R. Easier on your brakes and brake booster.
4Lo, CDL Locked or Unlocked, gear selector in "R", or while transmission is in 1st gear while "2" or "D" and engine speed under 3k RPM - Maximum braking assistance. Adds front wheel descent control if slippage is detected on an incline.
Source:
http://www.ezdries.net/Vidpics/ATRAC/LC100 new features.pdf
The difference between a "4x4" and an "AWD" transfer case is that an "AWD" transfer case doesn't have a differential, period. It's just two output shafts driven off of a pre-set gear ratio in the case. The shafts always spin at the same rate.
The center differential in an AWD case allows the F/R shafts to have differing speeds, enabling full time 4WD on high traction surfaces. Without ATRAC or a CDL, a "one wheel peel" would be possible, as you have three differentials in the system.
ATRAC allows you to drive on high traction surfaces, and drastically reduces, if not eliminates, the possibility of a one wheel peel, in 4Hi or 4Lo.
I can tell you, driving the Tacoma and other part time 4x4's in this stuff requires some thought, because if you DO get on pavement, you have to disengage 4x4, and then re-engage once on low traction surfaces. Driving in 4x4, without a center diff, on high traction surfaces, will eventually damage driveline components. I think that's a major win for full time 4x4 with a lockable CDL. For those who have mentioned Subaru, they have an optional feature similar to a Torsen center diff, and they give the user the ability to set the amount of resistance it has, from fully locked to like a 70/30 F/R split. If you drive it in "snow" (locked) mode on pavement, you'll grenade something.
The difference between an 80 and a 100, is that the 80 doesn't have ATRAC, but you can get lockers. On this stuff, I prefer ATRAC, because the lockers can get really squirrelly in a hurry. Off-road where you're going to be actually lifting a tire, I think lockers are preferable. Horses for courses.
In an 80 without 7 pin, the CDL automatically engages in 4Lo, eliminating the ability to drive on high traction surfaces in 4Lo. That's somewhat limiting, so the CDL button adds the ability to make that selectable. However, with the CDL unlocked, in 4Lo, and no lockers, an 80 is fully able to do the "one wheel peel." A 100, unlocked, in the same situation, would have ATRAC to brake the slipping wheel and send power to the drive wheel.
An unlocked 100 vs and unlocked 80 on snow and ice, would probably do better. An unlocked 100 vs a locked 80, the 80 would probably do better assuming the driver was capable of managing the slippage. Unskilled driver, the unlocked 100 is probably going to do better than the locked 80.