welcome back in the last lecture we talked about how ada lovelace and her friend charles babbage figured out how you could use punch cards to inner numbers and programs and processes into a numerical calculator well that was a great idea but in the history of innovation there's something important to understand which is that great ideas are a dime a dozen which you also need is somebody who can execute on those ideas which brings us to herman hollerith who was the first person really to use punch cards for a real working tabulating machine herman hollerith was worked for the u.s census bureau and in the and he was appalled that the 1880 census took about eight years to count they had to count all the returns manually do it by hand add them all up and he figured there must be a better way so he thought of the idea of using punch cards the punch cards as you see on the upper left are the ones that were used in jacquard's loom that loom that used punch cards to figure out how to do patterns how to weave the what right beautiful patterns that's the one that ada lovelace enjoyed seeing and helped apply the babbage's analytical engine but hollerworth also took the train and he you look in the lower left there's a you know train ticket and sometimes on the train the conductor would punch little holes in a code in a way to make sure that you know they identified the passenger gave him the ticket so the ticket couldn't be reused and the uh conductor might punch you know for somebody being uh tall or male or red-headed or sort of guess their age and we'd use little punches in it so that uh they could you know identify whose ticket it was and that eventually leads as you look to the bottom right to the idea of a punch card being used in a computer what herman hollerith did is whenever there was the data that came in he would take up to 10 or 12 traits of that came in on the census data such as age and uh male or female and you know different things that you would want to count married or unmarried and they'd be punched into the cards and he made a machine like that machine you see there and what it had was mercury in the bottom and a sort of electrical battery thing up top and so you'd put the card in and it would be able to notice because of the electrical current which holes had been punched and it meant that the 1890 census got done in record time now herman hollera's invention ends up becoming a company it eventually morphs in to international business machines or as we call it today ibm now like babbage the machine that hollywood used was digital if you remember what digital means it means it's digits sort of yes no on off one two three uh things that are discrete units the opposite of that is analog where it sort of comes in like a wave in which it's not discrete units now computers could have turned out to be analog here's an old analog computer and it uses gears and pulleys it's called analog because the length of the rope was an analogy for the numbers that you were trying to use and so people were trying to invent analog computers but for many reasons digital beats analog by the time we get to the 20th century part there's veneever bush we're going to hear a lot more about him he was an mit professor who helped run the u.s war efforts scientific efforts during the war and then started raytheon computer and you see he's invented something that's sort of an analog computer uses a lot of gears to show things but the person who came up with the conceptual invention to make computers that worked digitally was a guy named claude shannon absolutely fascinating guy among other things he worked at bell labs and would ride up and down the long hallways in bell labs on a unicycle while juggling he was very very eccentric but he was also very very smart there he is the great claude shannon and what he does is when he's working both studying at mit but working in the summers at bell labs he looks at things that the phone system has and the phone system creates circuits in order to route a telephone call and back then before transistors and microchips they use switches and if you see in the top of that picture the switches were sort of electromagnetic they clack on off on off sort of like an old-fashioned switch you might have on the wall of your house it goes click click back and forth yes no on off and it can do it not very fast but it'll go click click click click and it's able to switch on and off in a circuit what claude shannon figured out when he looked at these on off switches in circuits at bell labs was that those on all switches in a circuit could be applied to something called boolean algebra it was a type of mathematics that had been invented by george bull in the early 1800s george bull born in 1815 same year ada lovelace was born what george boole figured out was a way to use algebra algebra-like notations in order to do logical sequences in other words if you wanted to say this and this will result in that you'd have an and gate and you can see that the second one down on the left and there was a symbol and he even was able to say okay a b and you could use it to do mathematical equations you could figure things out using his notation symbol uh for logical sequences it could do a but not b it could do a and b it could do a or b it could do not a and b all these things were the type of things that you had to do in a logical argument in other words you know if the river is flowing high and the obamacare spillway is open then this will happen that's a logical sequence and those are the type of things that george boole was able to annotate using boolean algebra so what does claude shannon do he figures out okay you can do electrical circuits using on off switches and they can replicate all of the processes that are involved in boolean algebra for example look at the one on the left it's a serial circuit in order for the light bulbs to work in a serial circuit both switches have to be on otherwise it doesn't go in a circuit so that's sort of like a boolean algebra equation that has and in it this and this have to happen in order for a consequence to occur if you look at the parallel circuit on the right uh the switch either switch being on will light up one of the light bulbs they're in parallel you don't have to figure all this out it's not really that complicated but you can see how claude shannon figured out that you could use switches to replicate the logical sequences that george boole did in his algebra and so this guy's not even a doctoral student he's just an undergraduate at the university of michigan but he gets to mit where the neighbor bush the guy he was doing that analog computer is and the guy is trying to get a master's degree not even a doctorate and he writes what is the most important masters thesis probably ever written and it's called uh it's about the relay and switching circuits about how you can do logic in them and he wrote that it's possible to perform complex mathematical operations by means of relay circuits relay means just on off switches basically and it becomes the basic concept underlying all digital computers and so there you have claude shannon in his ingenious way working both at mit and at bell labs coming up with the way that digital logic yes no if this then that can be done by on off switches in circuits and in the end whether it's the iphone in your pocket or the computer you're watching this on it's basically just a huge amount of circuits with on off switches that then does logical sequences based on bits which are binary digits yes no 1-0 on off all of that is at the heart of the digital revolution thanks