Today computer hardware is based on integrated circuits. Its based on digital logic and use transistors etc...(i am not an expert) But looking on the history of computer hardware- First computers were all mechanical which I understand because of lack of technology. And after than computer were based on vacuum tubes. I don't understand what are these. What are vacuum tubes and how can they be used to make a computer? I understand todays technology, we have gates which can manipulate binary signals and using this we can do various stuff. But whats the basic idea behind vacuum tubes and earlier technologies? How did they work?