In the first one…
…his hair was spikey because of an explosion. In T2, he arrived with hair ALREADY spikey.
Skynet also updated the T-800 model to reduce the size of its jaw, add a self-awareness module that let's the T800 know when it is doing cool shit, and a built-in 'wound-but-don't-kill-people-and-then-later-pretend-you're-doing-so-because-a-10-year-old-brat-ordered-you-to'.
shareHaaa, you’re right about the jaw!
He’s also about 30 lbs slimmer. And by T3, he’s barely 5’11”.