Talk to him, just like you would talk to your hubby after a fight. Problem solving is more important skill and any problem or fight is only worth it if we can talk and learn from it.
"I" would tell him: I felt upset for what happen yesterday, I wish it didn't happen that way. Do you feel upset too? Do you understand why I react the way I did? I got really mad because you didn't listen and you could have broken the computer. What you think we should do so this doesn't happen again?.
Its a good time to talk about the feeling "frustation" because both of you felt that. Talk about what are better ways to react.
What is done is done and we can't bring the time back, we can only use it to make us better, and being a parent and a toddler is hard (yes, for both). Today is a new day, hug your son, hug your self and try to take the most out of what happen yesterday.
I would also give my older son a HUGE hug and tell him how proud I am of him, because I just can imagine how harder would have being last night if your older would haven't take it the situation as he did and that needs to be prize with words and hugs (and a extra long night story if possible).
You can add this to your "I thought I would never do that" list. If I showed you mine you would laugh!
Hope your kids and you have a better, easy, fun day today.
EDIT: I was thinking, only you and your kids know how things exactly happen, how hard did you hit him, how much of a tantrum he made, etc.
So if your guts are telling you that you should apologize then do it. Learning to accept our mistakes is another skill that we learn, I know some teens that have problems accepting any mistakes. Who would be great kids to their parents but would not accept any kid of mistake to others, as they take it as a sign of weakness. If this situations is something you think you can use to teach your kids about the fact that is of smart people to accept their mistakes then go, but of course only do it if you really feel you did something wrong that need to be an apology.
We all can take any experience, good or bad to learn.
So follow your guts.