welcome back today we're going to talk about the concept of software programming that's the notion of the code that you put into the hardware of a machine the hardware of the machine is all those transistors and vacuum tubes and circuits and wires and cables that are in a fixed position the code is just the instruction set something you type up and you just send into the computer using punch tape or any other entry method and that tells a computer what operations to perform that's particularly important when it comes to the idea of a general purpose computer like ad L LA talked about in the 1840s if it's going to be a general purpose computer it's got to be able to shift all the tasks that it does she even said it would do music and art and pictures as well as Ma mathematical numbers to do all that you have to change the instructions for how it operates and it of course gets expressed a hundred years later in the 1930s by Alan toring who says we don't need to have an Infinity of different machines doing different jobs in other words a machine to break the code a machine uh to do the missile trajectories a machine to try to calculate explosions a single machine will suffice he said and that was the idea in his mind of the universal Computing machine that he wrote about the engineering problem of producing various machines for various jobs is replaced by the office workor of programming the universal machine to do these jobs now uh most of the machines are almost all of the computers built in the early 1940s that we've talked about during World War II were single purpose machines whether it was the um even the eniac was mainly done to do missile trajectories uh Enigma uh the Colossus that broke the Enigma code in bedley park that was its main function now I did say that eniac was the first programmable computer in other words it was there it was made to do missile trajectories but you could reprogram it so it could do explosions or weather or calculate other things that reprogramming however wasn't all that easy it meant plugging and unplugging all sorts of cables you had to have a diagram of all the circuits and when you wanted to reprogram it to do something different it would take almost you know six or seven hours uh to reprogram it it was a job that the women did the women of eniac we'll talk about in a next lecture uh and it was because partly that the men thought the hardware was the most important thing you know boys with their toys but the women were given what they consider what the men considered to be clerical work which was figuring out the software how to reprogram it well the the person who really comes up with the notion of how to reprogram easily a general purpose computer not by plugging in all those wires and cables and then replugging them was a wonderful salty woman named Grace Hopper she was born on the upper west side of Manhattan and her mother was a mathematician and so she followed in her mother's footsteps and became a mathematician went to vas got her PhD in Yale now that was in the 1930s and you think well that's a pretty unusual path but no adah love LA and her mother from mathematicians Grace Hopper and her mother were mathematician in fact more women got doctorates in May during the 1930s then 20 years later in the 1950s so Grace Hopper is teaching teaching it faster uh teaching mathematics and Pearl haror happens and she decides she's got to enter the fry it's going to change her life so she does you know what uh moves her which is she divorces her husband leaves her husband joins the Navy at age 36 and she's sent up to Massachusetts to be in midshipman school and she graduates first in her class from midshipman school and becomes Lieutenant Grace Hopper of the Navy now she thought she was going to be sent to do coding cryptography like at Bletchley Park but in the United States there were a lot of Naval facilities that were trying to figure out how to break the German codes and how to do cryptography instead the Navy assigned a report to Harvard University to work on the mark one as I said the Mark 1 was uh the was designed and built uh by Howard aen and Howard Aken had joined the Navy he comes back to Harvard in 1944 and convinces Harvard and convinces the Navy that his machine should be a Naval facility so that the Harvard Deans didn't have too much control over it and so as you see there's everybody on his team who are commissioned officers in the US Navy and next to him is Grace Hopper the one woman on on his team uh aen gave Grace Hopper as soon as she arrived a copy of Charles babbage's Memoirs a copy of the notes on the analytical engine that Adel LEL had written about bages uh analytical engine and he even gave her some of the gears uh from the uh Difference Engine That Charles babbage's son had sent to Harvard and that Howard Aken had found in the Attic of their building so there's graceon her office and if you see behind her in the bookshelf there or in the shelves there there's one of the cogs and wheels of babbage's original Difference Engine and in some ways Howard aen there on the far left and uh Grace Hopper become the modernday counterparts of aah love LA and Charles babage in fact they almost thought of them elv that way they really and and and um Grace Hopper became a deep devote of AD love LA and even wrote notes on the mark one that were somewhat modeled on adal love LA's notes on the analytical engine she had done on babbage's machine and with her salty style and commanding presence she's able to hold her own with the other midshipman and Naval Personnel who were at Harvard running the mark one among the little things amusing things that she does she keeps a log and one day they can't figure out why one of the relays doesn't seem to be working there's some problem in the machine and they discover a moth that's caught in one of those click click click relay switches and she puts it in the log and she says first actual case of a bug uh and so she popularizes through this the not of a computer bug and how to debug a computer uh by the time she finished with it the mark one by 1945 thanks to Grace Hopper was the most easily programmable computer in the world it could switch task simply by getting a whole new instruction set you can see the paper tape rather than having to reconfigure the cables like they had to do uh with the eniac machine down at Pin uh the difference though was that the mark one at Harvard used electromechanical switches in other words those switches that would click on and off few of them were electromagnetic but they didn't use vacuum tubes the way uh eniac was being built down at pen sometimes when you're Innovative you also get stubborn and Grace Hopper and Howard aen the two of them got very stubborn about the notion of using physical click clacking Electro mechanical switches because they thought they were more reliable than vacuum tues indeed they were more reliable and when Hopper and aen go down to pen to see eniac they disparage eniac for not being easily reprogrammable and not being so reliable however it took uh uh could execute uh about three or four commands per second uh the mark one could whereas eniac could do 5,000 commands per second and so in the end obviously the vacuum tube and then eventually the transistor that replaces it makes computers all electronic and work real fast and once again with the eniac and that uh very fast machine that they were building at pen it was a group of women who we'll talk about in the next lecture who figures out the concept of programming thanks