In F1-2 you had damage threshold and damage resistance: http://fallout.wikia.com/wiki/Fallout_2_armor_and_clothing
Here is how it worked: http://fallout.wikia.com/wiki/Damage_Resistance
in fo1/2, you could also be hit for upwards of 2-3x your max HP in a single attack. 95% DR and 10+ DT was needed to survive a burst for 700 base damage. Gatling Laser is a perfect example in the old days... A burst from that on an unarmored target was minimum, 200-500 damage, without a crit for a potential 600-1500. Add in MA MK2 for 80% damage reduction, then 8-10 DT and the gatling laser was only going to hit you for 20-50. The math was a lot more complex then, or at least used bigger numbers for damage

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fo3/nv are not nearly as "hard" as the originals, but maybe thats why they are popular too
edit: i prefer using ncr combat armor, dt 20, only medium speed penalty, and they never see me coming, because they think im friendly

on VH its about as good as it gets, using unique displacer/bumper sword