The older series vehicles had Free Wheeling hubs, these basically disengaged drive to the front wheels, when you wanted 4wd you had to get out and turn the centre hub collar to engage the driveshafts to the hubs.
Later on came automatic locking hubs that would lock up when slip was detected.
Then with introduction of the Ninety and One Ten in 1983ish they had permenant 4wd through a centre diff.
The Freelander when it came out had a centre vcu that would asymmetrically split the drive power with more bias to the rear, when the rears started to slip or spin, the vcu would lock up and send equal power to both axles.