Lecture 10: Exciting Conclusion - CSCI E-1 2010 - Harvard Extension School

all right welcome back to computer science e1 tonight is our final lecture this here is an ipad it's not quite as wireless as you would like when we have to tether it to the room here but we're actually doing this as a test um both of us were a little disappointed to discover as were many people online that even though this thing comes with what's called a vga adapter or dongle one of these silly things that you have to connect to many laptops these days it actually the ipad does not have native supports for projecting to projectors which is to say i tried like 10 of the apps that came with this thing none of them actually project but we did find one we found that safari when you play a youtube video does actually project up there and as luck would have it we have a wonderful youtube video from 2006 from our own dan armendara so we thought we would begin with this youtube clip here wait wait i didn't make this video i'm just in it just clarify that hello my name is david maylen and i'm the instructor for computer science e1 understanding computers on the internet at harvard university's extension school you're watching one of our videos of the week for more such videos or information about this course visit us on the web at computerscience1.org enjoy the show so foreign i forgot about that part anyhow i i actually forgot i was in that but i should have paused it take it away okay so um hello everybody hello everybody welcome back um oh so okay i know what we're going to talk about so exam two we graded most of it except for the distinct distance exams we still have to um to do those we will do those very soon and we noticed that the vast majority of people got tripped up on some specific questions and so i just figured that we'd spend just a little bit of time to talk about those and specifically we're looking at the ones that involve the the snippets of code so the pieces of pseudo code um and unfortunately this seems to have um a lot of people seem to have move your ipad doohickey all right uh and is this computer on oh gosh the monitor's not on yet okay so i just figured that we would quickly um go over some of these oh sticky keys incidentally this is an example of a bug when you unplug a cable and then the computer just freezes with an apple logo on front this is an interesting outcome so buggy software i'm stalling you're not supposed to focus on me for what i had this something ready i was ready to start talking right when i start you should have been stalling this whole time and i'm like oh let's talk about this okay anyways um so each there were three pieces of code and you were supposed to find the error in each that was preventing it from doing whatever it said you were supposed to do so for example this first one it said that the following code should print 10 asterisks and the code was let i equals zero the second line is while eyes less than 10 and then you're supposed to print an asterisk and so i realized that this is way too small we will fix that let's see all right uh bigger 36 sounds good okay everybody can read that i hope okay so this was the code that you were presented so what's wrong with this why doesn't this work so keep in mind that what's important here is that we're not using any specific language you don't have to know java c any of those other languages that we showed examples but really you're just supposed to read this and and understand the concepts that we had that we had talked about in the programming lecture specifically the loops the if statements variables etc and use those to try to figure out why this pseudocode might fail so does this code print 10 asterisks no what does it print if anything a ton in fact infinite it's an infinite loop and why is that because 0 is always less than 10 right because 0 is always less than 10. we don't have an incrementer so i always remains at 0. at the very first line we set it equal to zero and we test in this while loop if i if zero in other words is less than ten and that is the case but because we don't have another line that says i plus plus or in other words i equals i plus one then i never increases so i never actually reaches the value 10. so for this reason uh it's always going to be run and this is an example of an infinite loop and so it was that just this i plus plus that you were supposed to do to correct this problem that that was it uh to fix this specific uh one all right so this one uh was let j equal to zero and uh let's see while j equals 100 if j is even than print j j plus plus all right and so this one says that the following code should count even numbers uh from 1 to 100 what what are you pointing at okay typo yes this was not in there let j equals okay so this was the code and so what happens in this case so it's supposed to print even numbers but what actually happens here what does it print if anything i'm sorry 100 why 100. um but well j equals 100. okay so good that's one way of interpreting this is that uh you're doing here another assignment and so in other words you're setting j equal to another another value 100. um but we could interpret this another way in that we're saying that this is actually a test so while j is equal to 100 and so this was either way is fine because it still leads to the same end result the same end fix but if we interpret this as a test as it can as a test in that manner then we say okay let j is equal to zero so that's the first thing while j is equal to 100 is j equal to 100 no it's not so this the contents in this loop this these lines of code are never run so nothing is printed whatsoever so what's the fix in order to have this code operate as we expect well i would say it's just j equals 0 while j equals 100 so j equals zero but then it says while j equals 100 i'm kind of i'm not really sure what that means exactly about those two lines so okay so the the first two lines are doing two different things so the first one is creating a variable called j and it's assigning that variable a value of zero so that when we look in memory we have this the space and memory that we're calling j when we look at its contents it represents the number zero and this second line is a loop and it's going to perform the code this code here that's indented so long as the condition so long as this boolean statement is true and so in this case we have to ask the question is the the value j equal to 100 in this case because we had set it equal to zero it is not so because this evaluates the false it's not true therefore this these lines of code will not be run the loop will just be ignored so if this goes back to the first if we look again at the first example that we had let i equal to zero while i is less than 10 uh print asterisk and then we had the fix i plus plus what we're saying here is that this is the same thing the very first line we are setting uh we're creating variable called i we're setting it equal to zero then we perform a test is i less than ten and it is because zero is less than ten therefore the the lines of code within the loop will be run but only that is only true if i is equal to 10 for example or if i is equal to 11 then that condition up here becomes false and these lines are no longer run okay so up here now we're saying let j equals let j uh be equal to zero while j is equal to 100 and so we we figured out that as a result of this it's never going to be run so what can we do to fix this how can we actually cause this loop to print out the numbers from uh from 1 to 100 in the even numbers specifically yes right so while j is less than or equal to 100 because in this case now what we are saying is that okay j uh if j is equal to zero then we will allow the the contents of this loop to be run if j is even then it will print j then it increments j goes back up to the top performs the test again now j is equal to one is j less than or equal to or is one less than or equal to 100 yes these lines of code are run so on and so forth all the way up to 100. is that clear that change okay now the last one you'll have to bear with me because it's a little bit longer to write so this one you have to loop forever and let's see i'm just going to indent a little bit less because it'll be a little bit easier to read so now we have another variable uh called k random number from 1 to 10. uh let's see if i can make this bigger all right uh so now if k is less than four then we're printing out print too low else if k is equal to 5 print got it right and program else if k is greater than 5 print too high all right so what this is supposed to do is this code will guess a number from uh by picking a random number from one to ten if it guesses the number five then it is guessed correctly and it will quit if it's any other number then it will say whether the number is too low or too high and then it will loop so it will pick another number and perform the same the same thing it will then test again to see if the number is 5 if it's too low if it's too high and it will print out appropriately but there is a problem with this uh what is the problem with this code why is this not being printed out yes it says end program before the last elsif so that's that's a good point but you might recall from uh else from if and else block the this code within uh within an ill and else block or an if block is only run if that condition is true so only when k is equal to five will it print out the words got it right and then it will end the program uh in all other cases uh it will just ignore that end program statement and it will continue along if we were feeling evil and we did something like this where we removed the indentation then you might have a better case because then you're saying okay well is that end program statement actually belonging to that else if block but in this case uh we didn't want that ambiguity so we just remained that statement or we kept that statement with that else if block so uh um right in the case of this pseudocode we're using indentation to figure out what blocks of code belong to various uh structures so this else if statement for example we're saying that everything that's indented uh underneath it belongs to that l-sit just like all of this code that is indented from the loop forever is belongs to that loop forever so all of this code belongs to the same block of code so we're just using indentation to demark what is a block of code belonging to which specific if statement or which specific loop sometimes and you might recall um some uh where's my cursor here some uh programming languages will use some character to to make it more specific so sometimes you'll see this in curly braces for example to truly make specific okay this the the blocks the the two lines of code between the the open and close curly braces actually belong to this elsif but in this case we're not using syntax like that we're just using indentation okay so other ideas yeah um what if the number is four that's a that's a good question so if the number is four let's see what happens so let's say k picks random number and that random number is four is k less than 4 no is k equal to 5 no is k greater than 5 no so nothing happens it goes back to the beginning of the loop picks another random number and it continues and so this actually goes against what we were saying it picked a random number and it didn't tell us what that number was in relation to the number that it was supposed to pick so this means that we have some problem with our if statements with our conditions that four is just being ignored so what's a potential fix that we can do to uh to get this working to include four k is less than five very good so rather than k is less than four we can just have k is less than five we have covered all of our bases is there another way that we could fix this to do the same thing less than or equal to four so in either case you really just have to change or add one character in order to get this program to function properly any questions on that what's confusing i was like how can i have something that's gonna forever ends then it right so what we are saying is that uh right with this loop forever we are not necessarily saying that um well we do need a way of getting out of this loop because otherwise it's an infinite loop and that could be bad there's there's obviously a point in at least in this specific case that we want to actually quit out of this loop and uh we can say loop forever and have it loop forever but in this case we did just want to quit after some point and the reason that we say loop forever rather than some other structure was that well what if it just doesn't pick uh k equal you know a k being uh 5 for i don't know 20 times or something like that then we then it's it's hard to guess that so it's hard to have a loop uh that tries to guess the number of terms that we would need so in this case we're just using loop forever to make sure that this code is run enough times before we actually find the k that is appropriate any other questions all right so one of the goals tonight is to tie up some loose ends and also to make sure that certain messages consumer oriented messages in particular sunk in so that when you exit this place and no longer for instance have a room full of classmates to turn to with technical questions or what-if questions you feel nonetheless prepared to make your way in the world of tech so what do we mean by that well suppose that one of your first stops after a course like this is to purchase come on is to purchase your first computer in let's say a while or you're at work and you have some input to the it people when it comes to getting your new work laptop and you tell them uh for the sake of discussion and we'll do it both ways quickly um that you want a mac and they say all right well you go ahead and pick from any of the desktop models and in fact this is something i myself just went through recently with my sister since we helped equip my mom um back home with a new mac and she was transitioning as an aside from pcs to mac but we'll do the other direction in just a moment so it looks like the model of interest to us is this thing here if only because it clearly has a monitor and it has a stand there are these things called mac pros but twenty four hundred dollars as a starting price is a little beyond my comfort zone so i'm going to go with the thing that comes with a built-in monitor so now you come here and this is where you the e1 graduates should hopefully have at least some new instincts with which to guide your next click so it looks like we have a menu of at least four options here where to even begin or perhaps put yourself in these shoes now you're no longer the purchaser but now that people know that you took this computer course at harvard extension it's now people who are turning to you to actually ask you for some counsel here so where do i begin i am a hapless uh non-technical person who knows at least how to check my email but i need a new computer so where do i even begin what should jump out at me in these listings yeah okay and let's see right here so good so if we zoom in on the two left hand options it looks like one of the first most striking differences is that the guy on the left has a 500 gigabyte hard drive and on the right one terabyte and what's the uh factor difference between these two just to be clear so it's twice as much 500 gigabytes plus 500 gigabytes gives you one terabyte so in fact you get twice as much storage space on the right hand side but let me push back uh it looks like they have the same amount of memory though so four gigabytes of memory four gigabytes of memory so what then is this difference between hard disk and ram and memory damn kind of give it away right because a lot of people maybe even yourselves up until a course like this conflated the term memory with different types of memory which are clearly in the computer so which is meant by which of these numbers what do we have four gigabytes of okay so ram and in a sentence the difference between ram and say hard disk space is what so storage and what do you mean by that okay perfect so the hard disk is for long term or persistent storage so that when you shut down pull the plug move the computer physically your data unless you've really jostled it or broken it is still there intact even though there's no flow of electricity to the device ram by contrast is volatile memory which is just a fancy way of saying lose power and that those contents are gone but ram is useful yes in the short term why what is ram used for precisely someone in the middle section if i may if everyone can say one thing today we'll have achieved our goal if we can set an arbitrary goal what is ram used for why bother with it at all yeah i'll take even the hesitant hand up for current processes perfect so for current processes things you're doing right at the moment hard disks as you may recall are pretty slow anything mechanical in a computer is relatively slow and there's not even that many mechanical parts we have the hard drive we have the fan but that's about it these days and they are in fact the slowest part so it makes sense intuitively hopefully that if you actually want to run your computer quickly and run your programs and interact with them you want those programs stored inside the faster type of memory which in fact is ram and as we discussed when we just depicted the pipeline of sorts on the on the blackboard long ago there's even faster types of memory than just ram called l1 cache l2 cache and those things start to get a little lower level you as the consumer probably don't really have to care as much about that but typically more is better but there are certainly limits but it's usually a function of which cpu you get it's not a user configurable drop down menu yeah that's probably the only thing they're gonna notice between these they're all gonna perform okay okay okay so that's a perfect mindset so if the if especially the end user who's going to be using this thing is fairly non-technical but they want a computer with which to you know check their mail write documents print things and that sort of thing what is in fact the most obvious difference someone like that is going to notice well maybe eventually they would notice the differences in hard disk space as their hard drive filled up but you plant those two things side by side on a desk or you take them to the store with you and yes as you know they're probably going to notice the disparate screen sizes the two ones on the left are 21 inches diagonally and the two on the right are 27 inches so that's a very reasonable starting point to sit this person down and say well which size do you prefer yeah okay so there are ways to mitigate even these decisions that we necessarily have to make right now in the short term before we pull the trigger but hey if we run out of disk space down the road we've you've all probably seen or at least heard of external hard drives you can plug them in with the usb cable they're relatively cheap and frank and the funny thing is when your friend runs out of hard disk space a year hence they're going to be even cheaper most likely and bigger so you can kind of ride that curve unless you need it right now okay so that's an interesting point and let me just plug out one of the buzzwords there so cores so what does it mean if a computer has multiple cores processors yeah and there's a bit of a difference so a cpu is not quite the same thing as a core because the cpu can have multiple cores but for all intents and purposes if a cpu on my on the left has one core and the cpu on the right has two cores it's almost as if you have two cpus here and one cpu here in other words twice as many cores means you effectively have twice as many cpus and in real terms recall now our discussion of scratch a couple weeks ago that means if you have two cpus or two cores the computer can literally not figuratively literally do multiple things at once and by figuratively i mean if you just have one cpu or one core clearly your computer seems to be doing all sorts of things at once you're typing a document you're receiving instant messages emails being downloaded but recall from many weeks ago that's really just an illusion that's because your computer is so darn fast it is toggling between all these various programs really fast really fast really fast doing smidgens of work here and there creating the illusion to us slow human beings that in fact everything's happening simultaneously but when you start to use more intensive programs like photoshop or if you're watching trying to watch a movie while doing work which i've been guilty of you actually want to be able to throw cpu cycles so to speak at those additional tasks and having multiple cores can help with that so which is perhaps obviously the most souped up model here in this menu of four options right so the quad core and that's where they're trying to upsell you or at least entice you in the top right there there's that little blue icon that says quad core so you can just infer from that basic definition quad core pretty much means it's as though this thing has four cpus but then the e1 graduate in you should start to kick in now wait a minute i am just a relatively slow moving human being and yes i might multitask and hit alt tab or command tab a lot but the reality is a normal person is probably checking their email browsing the web writing documents printing things maybe watching a movie but if you're not using photoshop or developing movie content and editing videos like the one we began with tonight you might very well be overpaying so you have to try to find at least intuitively that fine line if money is no object then by all means go with the highest end model possible but you have to realize too that if you ride that curve of technology all the way to the right getting the latest and greatest the reality is six months from now apple's going to release something even better or whatever the company happens to be so you're paying that premium here well if we toggle over for just a moment now to the first uh the first thought process you might have for a pc i picked dell it's a popular pc company in this case i'm gonna want a laptop but i want one of these newfangled things that i keep hearing so much about called netbooks what is a netbook yeah so it's a smaller pc a laptop form factor that's generally used to go on the internet and the funny thing is in my own personal opinion this is a stupid new term it just means small laptop and we've had laptops for ages but now you slap a new buzzword on it you market it at a different price point and you can call it something new but the reality is these are still devices that have maybe one gigahertz of power maybe 1.3 1.5 gigahertz of cpu power if your needs are relatively humble even though you propose using it for internet and email and the like you can absolutely write an essay on something like that and send documents to a printer and look at photographs watching movies you might get some buffering and some stagnation when you're trying to play the movie if you're trying to develop movies probably not the right device but the beautiful thing is that if you click through to these kinds of devices if i go down here to let's click on shop now what's really compelling is my god like the starting price points of these things tend to be two hundred dollars three hundred dollars and what you get actually this isn't even the right one these are normal pcs those are normal laptops uh let me go to mini notebooks so now we get to the price points of like 279 dollars 299 dollars so i actually have one of these little toys um it's a dell mini nine it's the which means nine inch screen um there is one gotcha to this and the problem with buying things online whether it's for at least apple you can go to the store dell doesn't really have storefronts though you can sometimes find them in best buy and the like what's the problem potentially just intuitively with a netbook so yes and no so you propose you can't multitask you kind of can you can certainly hit alt tab or equivalent and run multiple programs at once if your system if your taskbar is starting to get 10 and 12 icons you're going to notice a slowdown but you can absolutely have say a browser open word your instant messaging because frankly if you think back four or five years we probably were all doing that four or five years ago and our cpus probably were not even as fast as these things have now if you want to run the latest and greatest software like windows 7 and the like then that costs you cycles for other reasons but that's fair there's certainly going to be a limit and i think you are inclined to propose another limit it drives me nuts i actually don't use my little netbook because it's too annoying to type on for very long whereas small laptops historically for me small but at least i don't feel constrained i mean this one i literally am like this and i just can't do it but maybe other people can but certainly for using just checking your mail or tossing something in your backpack cheaply and quickly it does perhaps make sense though if you read the media the um these things called ipads are a claim to be taking a bite potentially out of that market so we shall see all right so another scenario so you now walk into starbucks this one now you already own a laptop uh or this is your friend and they are now a little bit paranoid because of things you've told them about all of these threats out there so you walk into starbucks you own a laptop and this starbucks is advertising wi-fi free wi-fi or frankly maybe hubbard university across the street has free wi-fi and you're trying to patch into it so what should be going through your mind like what are the gotchas okay security and what do you mean by that just anything that you're doing on that laptop you know make sure no one else can see what's going on okay good so if you are on a wireless laptop and by this we mean you are using that protocol called 802.11 a or b or g or n you need to be cognizant of the fact that there may very well be people with too much free time or malicious intent watching everything you do not over your shoulder but just wirelessly by sniffing the traffic now there are technologies that mitigate this what were some of those buzzwords or technologies that mitigate that concern okay so using a vpn a virtual private network unfortunately the normal person off the street doesn't generally have access to a vpn unless you have a corporate network or a university affiliation but if you do have those connections you can usually ask the it folks for some free software or software they've paid for so that you can use it you have a username and password and this lets you have an encrypted tunnel over an otherwise insecure connection now that's good for keeping away the annoying people who are trying to observe what you're doing there it does not stop who from seeing what you're doing well hackers it would i would argue most hackers it would stop because all they would see is scrambled nonsense zeros and ones that look random because your boss exactly right someone there's gonna be uh the buck stop has to stop somewhere and if you're vpninting into your corporate network or university surely the people at the other end of that tunnel so to speak have the ability to see what you're in fact doing what are some other buzzwords so you don't have a vpn what at least could you expect in a public space or certainly in your home for security's sake okay so using a firewall and a firewall is something that comes built into a lot of operating systems these days or it can be a physical device that protects traffic protects you from getting hit by any form of inbound traffic by only allowing outbound traffic encrypting your hard drive is a way to obviate physical uh to ward off physical threat or just nosy employees if you hand something over to like geek squad or the like so encryption on your laptop and where else could there be encryption https okay so using https to shop on amazon or some other otherwise uh sensitive site where you're giving private information and what about wirelessly what are the protocols you're hopefully using at home if you have any wireless at all wpa and okay so that's good wpa you might see it wpa2 which is a newer variant the bad one to avoid or at least if you only have it you should probably spend 20 30 bucks to get a new router before long wep so wep and it's actually interesting there was just uh one or more articles published recently about how some manufacturers in china i think have been getting clever about manufacturing dedicated devices that you allow them to listen to some wireless traffic and they crack wep keys for you and then allow you to connect wirelessly to someone else's network i mean it is relatively that easy and they're now just packaging it up various companies to save you the dirty work so you have all of these means of encrypting your traffic but what actually happens when you bring your laptop to starbucks and you connect it so you might recall that we have this this alphabet soup of all these acronyms of all these various services that are responsible for bringing a computer online uh and and allowing you to connect to the internet and start browsing the web so let's say i bring my computer to a starbucks and i connect through maybe they probably don't have wpa protection but just assume that i'm connected to their network what has to happen how does my computer start to send data how am i actually able to type in a url into the web browser and get a web page back what's the sequence of steps or what's the first step arguably that that my computer has to has to accomplish in order for this to even begin happening so bring my computer i sit it set it down and what do i need in order to allow my computer to start communicating on the internet yes okay great so i need an ip address and so typically an ip address is not something that my computer just has so how do i get an ip address from the air what happens okay so so my computer when it connects to the router it actually contacts what's called dhcp server and so this dhcp servers most of the time it's built into uh to the router so what we what we are calling these home routers that david was mentioning earlier they might include their own firewall it might have wpa protection all of these things but actually includes a variety of services and one of them is dhcp and dhcp provides a variety of information to my computer when it's requested including the ip address and including some other servers known as dns servers so these dns servers are ip addresses that my computer connects to to do what right so the other way around so it translates so given a domain name like cnn.com or computerscience1.net for example it will translate that into the ip address of the server that my computer needs to connect to in order to communicate and to be able to send data to and from to receive a web browser or to receive a web page itself okay so now my computer has received this information and so i'm able to start typing in a domain into the web browser when i hit enter what typically happens to this this data well recall that usually this this information is sent it's broken down into various little packets and it's sent along the router along the the wire from router to router and recall that what we're calling the router is is it has a lot of stuff packed into it like i mentioned before it has all of these servers packed into it but it does also serve as a router and the purpose of a router is to retrieve these packets of information try to figure out where to send it next so it knows okay well ip addresses in this range should go this way i appear addresses in this range the package should go this way so it figures out where to send the packets next and sends the packets to the next router until ultimately those packets will be received by the server reassembled and then the message will be received and typically these messages especially with web servers or when we're trying to view web sites will operate over the http protocol and so using http that the computer as you might recall asks the the server for uh let's see what you do with the chalk here it is so it asks the server uh to get some information in this case a slash and so what does this slash typically mean when we're talking about http so there's the computer request get slash what is it asking for from the server so i've typed in a web i've typed in a website like computer science1.net i've hit enter and all of my my request has been broken down in the packet sent over the wire from router to router reassembled on the server and it's this message so it's asking to receive a web page from the server and the web page that's asking for is this slash and what does this slash represent right the home page or the default page that's provided by the server and typically that translates to that index.html and recall that html is different from http so don't get the too confused http is the protocol through which the computers and servers communicate to send uh web pages and to request web pages whereas html is just a markup language it's just a way of formatting text that the computer or the server sends to the client computer to my computer that we that the web browser reads and then interprets into an actual final web page so it's it's two distinct things and it's important to keep the two separate okay so as soon as i my computer has requested the slash or the index.html the server sends that data back to my computer and then i'm able to display that web page on on my computer and so um recall that we can have a variety of problems that can exist through this so let's say for example that i'm no longer able to connect to the domain name serv so so i can no longer connect to dns and i type in a domain like computer science1.net i hit enter and it says that it can't resolve the information well sometimes there's ways around this and troubleshooting problems like this it really becomes an issue of uh well where is the problem occurring is it because i actually cannot connect to any web servers on the internet at all is it that one of these services is down is it that dh the dhcp server is down then i'm not actually receiving an ip address it said that the dns server is down that and i can't translate domain names into ip addresses and it's typically very different things that that can that can happen and if you are able to figure out which one it is then sometimes you can get around it so if a dhcp server is down it's probably a little bit difficult to just guess an ip address and have it operate but if the domain name service is down then maybe you can give it a separate domain name server uh to to operate on uh and be able to translate your domain names into ip addresses all right so that's a look back at where we began with hardware transitioning to networking and security what are the kinds of trends that are useful to be cognizant of as you step out beyond computer science e1 so there's this really popular buzzword de jour these days which is called cloud computing does anyone know what cloud is meant by cloud computing actually step back has anyone heard this expression before okay so you've almost all heard it so what is it yeah um i'm very vague about this and i'm kind of guessing but it's kind of putting your information on a server okay okay good so it's it's cloud computing is all about storing your data and even running your programs in this this newfangled thing called the cloud the reality is this is really just a new word for outsourcing frankly and that's a bit of an oversimplification but this is just yet another one of these buzzwords that everyone likes to jump on the bandwagon for and start touting it as a newfangled technology when reality all people are beginning to talk about or beginning to do is relabel things like gmat where do you keep your email well i keep it in the cloud well a year or two ago we just called that the web or gmail.com now there is a greater sophistication tout or there is a greater vision behind cloud computing and that idea is that no longer before long will you have to run programs only on your own cpu on your own hard drive in your own ram rather when you want to write a document you instead pull up the address of some server and start typing away those of you who already use google docs or google spreadsheets these kinds of web-based applications are already using this thing called the cloud and now microsoft just this week is beginning to release what they call microsoft office online which is similarly a free suite of tools whereby you have a word processor a spreadsheet and even a powerpoint like or slideshow type software available to you for free and when you actually save your data similarly is it not stored locally on your own laptop or desktop but rather where yeah so on one of their servers so now the flip side of this is that if you are seeing an employee at a company that is no longer paying three hundred dollars five hundred dollars per copy of microsoft office which is ridiculously expensive albeit quite popular and are instead using a relatively cheaper service like google docs or google apps you can actually long story short pay someone like google to host your website foo davidmailand.com but that actually lives on google servers and all of my employees can go to davidmailin.com and write documents there write letters they can make their presentations they can store their spreadsheets so you have this nice illusion of owning the software or owning the domain name even though someone else is actually hosting the software but what happens at 2 30 pm if you really have to bang out this letter to an important client and bam something bad happens what could be that something bad in this scenario perfect so you're in you could have internet connectivity problems maybe it's google servers that are having issues that's certainly been known to happen maybe it's something silly like your router got unplugged maybe it's something a little more beyond your control like verizon is having an issue with their network or comcast is having an issue with their network long story short you are now sol you cannot use that software because it's in the so-called cloud so that's sort of the flip side of what otherwise is a cost-saving measure now in fairness eve there are things that can plague our computers these days even if we don't even have this thing called the cloud there's no hosted applications we're just using microsoft word on my own laptop or pc what can still happen in this day and age that could go wrong just think about reality what could go wrong in a current it if we scenario on the cloud would be safe you drop your computer down a flight of stairs and the hard disk is broken okay so that's quite fair too right right now you are very vulnerable to physical damage or just circumstantial damage like your hard drive just gives out it's defective and bad things happen well the reality is there might be some value to paying even if it's only a few dollars per year per month people who are more technical than i or more interested than i in actually solving the problem of data backup so right now we have this problem this might ameliorate it but what about the electricity going out in the office well i'd argue that you know frankly you still can't send that or write that important letter if you have these real world constraints but long story short this is at least a technology if you will to be cognizant of because more and more are we humanity likely to transition more stuff away from our own client machines as we'd call them to the so-called cloud or really just to a server environment yeah absolutely so now it becomes a much juicier target if your stuff and your confidential information is stored along with all sorts of other more interesting information but now you're in the same bucket as all of these other folks frankly and we even talked about it a bit in this class encryption frankly is a pretty decent solution to these problems whereby yes all my email all my documents may very well be stored on servers owned by google and they don't quite offer this feature across the board yet but the reality is in a few years once people begin to expect this level of support and cpu cycles are such that we can spend those cycles on more and more encryption a lot of those problems can be mitigated by having even per company keys encryption keys so that your data even if it's in the same place can be encrypted in a different form than someone else is all together but there's this other there's this other feature that's related to this that we thought we'd introduce you to just a taste of because it actually lets you experiment yourself so when computers first began to get popularized they were pretty dumb devices they were dumb terminals or thin clients is another expression for this whereby you had a pretty basic pretty you know bare bones machine on your desk but when you started typing you were actually doing real work on some server elsewhere and that's kind of where the world is trying to get us back to over the past 10 20 years we've migrated to this world where you buy shrink wrap software or download it install it on your computer you have antivirus computer all of us are independent computing entities and any number of things can go wrong with our computers and frankly i hate this reality i think the fact that so many of us struggle with i.t issues and technical issues and for those of us who actually own multiple computers whether it's a phone a laptop a desktop just keeping all of those things in sync is a complete nightmare and it's not an interesting problem to solve so there are some consumer oriented values to these uh this thing called the cloud but the cloud as it's called is ultimately the result of advances in what's called virtualization and this is another sort of buzzword du jour but it actually describes a real technology the upside of our having so many cpu cycles at our disposal and frankly so many cores is that we at the moment don't really know what to do with all of these cores especially larger companies that have big servers that have 4 or 8 or 16 32 64 cores inside of a one and a half inch tall computer what you do with those is increasingly less clear and so what because long story short we are not very good at writing software that takes advantage of that many cores of that many cpus we really write software typically that just needs one cpu maybe two to do something to get real work done so what the world has started to do is chop up these physical servers and all of their cores and see the illusion of multiple servers whereby you can buy one server have a lot of ram in it and a lot of cores and then you can rent space on that server to ten different clients and to each of those clients you give two cores and maybe a gigabyte of ram now how do you do that without you don't have to give them accounts on that system you can instead what's called a virtual machine software virtualization software and this is special software that creates the illusion that one physical computer is actually multiple other computers each of which has its own administrator account each of which has its own choice of operating system you can run windows xp you could run windows 2008 you could run ubuntu linux you could run red hat linux all physically on the same server so long as before you install any of those operating systems underneath it all in a sense you put some special software called a virtual machine that creates the illusion that one physical box is multiple servers and the cool thing is and this is where we're getting to you can do this yourself these days for free even on your own laptop on your own desktop especially if for instance you're a mac user and you'd actually really like to have a pc for just occasional applications to use or conversely you are running windows and you'd actually really like to learn a bit more about this os called linux but you don't want to delete your whole hard drive and start fresh you don't want to do this thing called dual booting because if you're like me you're never going to reboot your whole computer just to change operating systems it'd be much nicer if it's just another operating system running in a window in your own comfortable environment so there's this program which we would encourage you after this course just to google for download for free and poke around it's pretty good in terms of documentation and tutorial videos but the one i have up here is called virtualbox it's made by a company called sun microsystems which was just acquired by a company called oracle it's still free software and what's beautiful about it is that it exists for macs pcs linux computers other linux unix-based operating systems and it looks the same across all of them so it's nice from a sort of familiarity standpoint and what it lets you do is create the illusion of a machine computer i just click the new button i'm going to ignore this boring text here because the next questions i'm going to be asked are what do you want to give the name of this virtual machine i then tell it what operating system i plan on installing i'm going to put windows xp on here i click next i then tell this program how much ram do i want to allocate for the operating system i want to install on top of mac os so right now i'm going to treat my laptop as though it's one of these servers with lots of cores now this would be kind of ridiculous because this is not a very fast computer this air so i'm going to be a little reasonable click next i can create a new hard disk this is a software-based card disk so it's really the illusion of a hard disk it's not a physical device and if i click next again i'm going to skip a couple of these details how many gigabytes do you want to allocate to this virtual machine i mean i'm really creating a computer in software and the end result is going to be an icon much like this one here whereby if i click windows xp service pack 3 a windows going to open and i did this previously so it's waking up essentially and i was actually amused to discover that the last time i used this virtual machine was on a plane so i could play a game from the 1980s called king's quest and i did that because i really wanted to play this game i only had a mac at the time on the plane and i did have a virtual machine running windows xp so as stupid as this is this is what graphics were like in the 1980s and yeah so this is king's quest wonderful game but you can't play it on modern computers in fact you have to kind of slow them down so that the guy doesn't tear across the screen but i am going to go ahead and just quit this for a moment so that you see underneath this is do thou truly wish to cease our adventuring yes quit and what you see here is windows running on my macintosh and that's the takeaway and what i also have in another window here if you'd like to be even more of a geek and experiment with another os altogether this is what ubuntu linux looks like this is a free operating system you can download a cd or an image therefore and install it into another virtual machine and voila your mac is now running windows it's running linux and slowly if i'm doing all these things at once but this again is all takes advantage of the technologies we've been talking about thus far i feel like a hand was about to go up yeah with licensing any issue with licensing yes you have to own that copy of windows that you install on this computer and we have a site license for it at harvard for that purpose ubuntu and other linux flavors are generally free so it's not so much an issue and just fyi apple does not allow legally people to virtualize mac os so if you own a pc you can't quote unquote run mac os in a window on your computer but people have figured out how to do this all right so i think it's time to come full circle tonight with a look at programming i think dan has volunteered in advance to help us out with this and we need just one other volunteer we can take a moment and uh take a second in a moment to change tapes as we set up a little table but we need one volunteer who's very comfortable being on camera and who's going to help us execute the very last computer science e1 program ian come on down all right now before we reveal what's in the bags and what ian has to do with you is let's go ahead and actually we kind of did this in the wrong order uh an astute student we'll figure out preemptively what we're about to do no that's okay once you've gone up awkwardly to the front there and let me go ahead and open up just a little program i can do that if you want what do you want to be the one over here i got it you sure yeah all right all right so before ian and dan do uh battle wits here we need to get some little audience participation so the goal at hand i'm really hungry i didn't really have lunch today so i would really like a peanut butter and jelly sandwich all right but we're going to ask the audience here to help teach us the computer teachers and ian how to make a peanut butter and jelly sandwich and then we will execute that program and hopefully there will be no bugs and i will get my sandwiches output all right so with that said you guys don't get to talk just yet we're going to ask the audience and i'm going to document this and then you guys will do the execution this is sort of a weird abuse of microsoft word but i really just need some place to type since it's kind of boring to write it all down on the board and change my margins all right so step one in my program and you may assume the following we apparently have some bread came prepared we have some jelly we have some peanut butter and we have some knives and some paper towel so hold that thought for a moment while we go ahead and change out tapes and think to yourselves for the next 60 seconds how do i actually make a peanut butter and jelly sandwich and that's all we have information that's all we brought so that's all you have like what's on the table yes you may assume you have this as input so i guess you're not worrying about contaminating the jam well we shall see all right step one tell me what to type and then they will execute immediately all right wow you're really taking big bites out of this problem quickly all right so open bread so don't execute yet when we write down a few steps and then we'll execute open bread uh peanut butter and jelly okay someone else step two yes hold night okay step three okay oh wait tear off one square of paper this will be real good group activity here okay yeah lay paper on table this is gonna be fun all right lay paper on table step five someone else get the bread i look forward to seeing that precision okay next it's gonna be quality scoop two slit remove two slices of bread okay remove two slices of bread okay step six sorry place on the paper towel place on paper towel a few more steps scoop peanut butter peanut butter with knife okay spread peanut butter on one slice of bread actually you should put on both sides actually put on both sides on both sides okay oh and both slices okay both slices whoops let me kind of shrink the font okay spread jelly on second slice we'll do two versions take us home someone put knife down yep next step put slices together peanut butter and jelly together put peanut butter and jelly slices okay loop three times that'll be good okay all right so this is pretty good we seem to have some form of output here let's go ahead and execute and then for version two and final we will see if we can't improve yes we're sort of doing this in parallel so ivy this and he does that if he does something i don't consider it done until i do it correct so what will i recite the instructions and i would do your best to put blinders on not look at what dan's doing unless he lead you astray or vice versa and uh you must only do what we tell you to do right you are a computer right when computers are told what to do they do it they don't assume or make guesses or fill in the blanks for you they're not that smart so step one open bread peanut butter and jelly and don't look at that oh right isn't that your silverware yeah yeah i think one of the computers is taking some liberties here it says open jelly all right all right very good hold knife oh crap good that too is imprecise tear off one square of paper that's a rectangle paper yeah what do i do with it well wait we're waiting for your other computer okay all right lay paper on table this paper has hearts on it that's nice get the bread all of it the remove two slices of bread scoop peanut butter no no place on paper towel place what on paper towel place on paper towel you know this will be the video we're showing on youtube three years from now scooped peanut butter with knife a scoop peanut butter with knife we seem to well all right spread peanut butter on one slice of bread i think ian's right we never told you to put the bread down we said get the bread what we said get the bread no you said put put place on oh we did but you also didn't specify which bread i was supposed to put it on so i just used the ones where you cook the two slices or the entire bread that's true all right let's forge ahead then oh right actually put on both slices it already is there's another piece of the knife over there all right spread oh let's see spread jelly on second slice yeah that jelly was there when we came in put knife down put peanut butter and jelly slices together okay not quite edible shall we take one final stab at this all right so let's um assume things are in as pristine a condition as possible but we'll take some liberties now let's go back to the drawing board here and see if we can't fix where we want to stray so step one please on loaf of bread okay remove cap from peanut peanut butter and jelly yeah okay okay so we'll allow you to go back to the same step but not further so unscrew caps from peanut butter and jelly yeah move two i'm being a lot less reckless this time it seems yeah step three it's gonna be boring tear off one rectangle of paper towel place rectangle on table on top surface of table any naysayers yet alright next step yep remove two slices of bread take off two slices of bread take out two slices of bread from good we're we're learning open end of bag okay so this side's being quiet yeah place the bag back on the table that's for ian there put the slices okay place the side by side on paper towel okay think we got that one through pick up knife do not break it pick up unbroken knife good thank you from handle next of knife into peanut butter i'm going to push back i claim there's a bug here yeah so what we do in step one uh step two yeah so that's kind of yeah so remove caps from pb and jelly hubba all right place caps on top of table um how are we holding the knife where do we pick pick up knight oh yeah yeah with hand that's fair okay bring us home almost there what's that thank you all right what else lift scoop do you understand scoop i don't understand scoop insert blade of knife into peanut butter what do you want to do scoop out all right we're gonna we want to assume that you know what scoop means tablespoons with uh two t two yeah tablespoons of peanut butter of peanut butter with knife all right that's pretty good next spread oh come on it never works out well when you say it's so succinctly okay spread peanut butter on one side okay good top side of bread one slice spread evenly okay shrinking the font yet again all right a couple more steps before this gets even more awkward peanut butter side up back on paper towel oh okay well you can spread it on the tape with the bread on the table right okay all right so it seems we don't need this one what's next yeah everyone's leaving with a peanut butter and jelly sandwich tonight so we better start being hygienic clean the knife better hope you get bread from that one only 20 more sandwiches to go all right clean the knife and all right a little copy paste job blade of knife into sure jelly jelly okay on this okay so on one on top side of of the slice with no peanut butter okay and finally match up jelly touch in the center evenly even so that the edges match loop twice all right anything else is that it all right here we go your exciting conclusion untwist tie on loaf of bread fix the knife untwist untwist tie on loaf of bread oh no well all right we'll improvise all right all right unscrew cap from peanut butter and jelly you guys are boring no fun didn't say remove what didn't say remove tear off oh and jelly and jelly tear off one rectangle of paper towel go ahead well i they just wanted one they didn't say one there that's one rectangle all right place rectangle wait a minute you're gonna jump in the gun what well now place rectangle on top of surface of table on top of surface of table there on top surface of table yeah done take that sentence is not grammatically correct according to microsoft word okay take out two slices of bread from open end of bag oh out place the two slices no place the bag back on the table place the two slices side by side on paper towel gently pick up unbroken knife from a handle with hand you guys are that's not fair well i fixed mine so see not broken do not break it not broken remove caps from peanut butter and jelly you guys didn't leave me a free hand you were supposed to unscrew it though i did unscrew it it was unscrewed it's just there wait it didn't say okay place caps on table insert blade of knife into peanut butter here we go oh no oh no well that was up there you didn't tell me i hope you're getting this i can't do it scoop out two tablespoons of peanut butter with knife that actually makes a pretty good spoon now spread evenly peanut butter on top side of one of the two slices they were well i i placed them side by side but due to physics they moved elsewhere oh man is okay okay clean the knife almost done clean the knife four steps till we put you out of your misery no god no it's e coli clean the knife insert blade of knife into jelly scoop out two tablespoons of jelly with knife spread evenly jelly on top side of the slice with no peanut butter peanut butter see it's nice like this where distance ed is really looking better isn't it all right and finally match up slices so that peanut butter and jelly touch in the center evenly so that the edges match all right well a big round of relieved applause all right do your thing where you say hello everybody and we wrap up goodnight everybody we will be in touch by email with the courses conclusion grades and all of that but certainly do feel free to linger if you have any questions tonight or want to chat and many thanks to our volunteer tonight you