1 00:00:01,260 --> 00:00:06,900 OK, so we're going to go over some new topics in the next section and kind of require us to know a 2 00:00:06,900 --> 00:00:09,150 little bit about the computer's memory. 3 00:00:09,630 --> 00:00:13,170 So I'm going to provide a quick explanation on that. 4 00:00:13,560 --> 00:00:19,650 And then later on in the course, I will go a little bit deeper in a computer memory so we can really 5 00:00:19,650 --> 00:00:24,600 get into the weeds and you can understand what's going on under the hood in that digital kind of imaginary 6 00:00:24,600 --> 00:00:25,590 space on your computer. 7 00:00:27,300 --> 00:00:30,810 So where does the information in our code get stored? 8 00:00:31,050 --> 00:00:37,530 So we've talked a bit about the compilation process of using the C++ compiler, right? 9 00:00:37,530 --> 00:00:43,200 But what happens when we actually run our program, what's happening inside of our computer? 10 00:00:43,200 --> 00:00:44,130 What is it doing? 11 00:00:46,050 --> 00:00:53,670 So what happens from a very high level view is that our executable that we've created from the compilation 12 00:00:53,670 --> 00:00:57,150 process also can be referred to as our binary program. 13 00:00:57,780 --> 00:01:01,500 It gets loaded into a place we call virtual memory. 14 00:01:03,160 --> 00:01:07,990 So another note here, you know, operating systems and memory management are complex right now, we're 15 00:01:07,990 --> 00:01:11,020 just looking at it from a bird's eye view of very bird's eye view. 16 00:01:11,890 --> 00:01:17,590 Later, we're going to go a little bit more into memory and I say a little bit because this is an operating 17 00:01:17,590 --> 00:01:20,560 systems course or a computer architecture course. 18 00:01:20,980 --> 00:01:28,720 I just want to kind of give you on the tools you need to be able to write software and understanding 19 00:01:28,720 --> 00:01:32,110 memory and addresses and things like that are important. 20 00:01:32,590 --> 00:01:34,720 So I will have to go into it a little bit. 21 00:01:36,520 --> 00:01:39,050 So what is this virtual memory thing that I just mentioned? 22 00:01:39,070 --> 00:01:42,370 Well, we call it virtual because it's not a physical thing. 23 00:01:42,700 --> 00:01:48,460 We do have some physical things on our computer that deal with memory, and that would be RAM and the 24 00:01:48,460 --> 00:01:49,600 hard disk drive. 25 00:01:49,780 --> 00:01:55,070 So the hard disk drive is basically the spinning disk on your computer. 26 00:01:55,090 --> 00:02:00,760 It can be made of silicon and metal and plastic and stuff, and has a little reading and writing head 27 00:02:01,180 --> 00:02:07,360 that you can think of kind of like a like record player or something like that. 28 00:02:08,740 --> 00:02:15,520 But that is something that stores memory permanently the hard disk drive. 29 00:02:16,000 --> 00:02:21,190 So it's something we would call non-volatile, so you turn your computer off and stuff is still stored, 30 00:02:21,190 --> 00:02:24,940 you don't you lose all your files that you've saved onto the hard disk drive. 31 00:02:26,450 --> 00:02:33,380 You also can have a hard disk that is not necessarily a disk, it's kind of like maybe a solid state, 32 00:02:33,380 --> 00:02:37,400 so you might have that in your computer so it doesn't use a spinning disk, but essentially the same 33 00:02:37,400 --> 00:02:37,730 thing. 34 00:02:38,780 --> 00:02:45,500 The RAM is also a physical thing that you can touch their sticks of RAM memory on your computer. 35 00:02:46,550 --> 00:02:52,190 That's what a lot of people refer to when they're talking about memory, and that is something we refer 36 00:02:52,190 --> 00:02:55,470 to as volatile storage, so it is not there. 37 00:02:55,490 --> 00:02:58,820 Once you turn your computer off all the data in there, it gets wiped in the RAM. 38 00:02:59,510 --> 00:03:01,510 But the virtual memory is something else. 39 00:03:01,520 --> 00:03:04,720 So you can basically think that it is. 40 00:03:04,730 --> 00:03:06,650 You can imagine it being in RAM. 41 00:03:07,340 --> 00:03:11,030 Somewhere where our programming was stored is pretty complex. 42 00:03:11,030 --> 00:03:17,060 It's managed by the operating system, but we're just going to imagine it somewhere in RAM and it's 43 00:03:17,060 --> 00:03:18,680 just an imaginary space. 44 00:03:18,680 --> 00:03:20,540 It is not physical, it's not. 45 00:03:20,540 --> 00:03:21,890 So it's not a physical thing. 46 00:03:21,890 --> 00:03:29,930 It's just some kind of area like set aside, you know, that RAM, your RAM has a certain amount, right? 47 00:03:30,830 --> 00:03:36,980 So you might have, you know, whatever amount of RAM on your computer and you'll have this virtual 48 00:03:36,980 --> 00:03:40,880 space, this part of RAM, where our computer program can get loaded. 49 00:03:42,030 --> 00:03:46,140 So it's a little more complicated than that, but that's what we're going to imagine it is right now. 50 00:03:47,640 --> 00:03:54,750 So some other things to talk about is there's big distances between some of these locations where you 51 00:03:54,750 --> 00:03:56,280 can grab your data from. 52 00:03:56,280 --> 00:04:02,430 So I'm going to compare RAM and the hard disk drive with some illustrations. 53 00:04:03,030 --> 00:04:07,680 Another note down here remember that RAM is only volatile, so it's temporary. 54 00:04:07,680 --> 00:04:11,760 When the computer turns off, the data goes away. 55 00:04:11,790 --> 00:04:12,060 Right? 56 00:04:13,050 --> 00:04:14,820 So let's look at a little analogy here. 57 00:04:14,830 --> 00:04:19,020 So here's a room this square that's gray, and here is you. 58 00:04:20,500 --> 00:04:27,670 And here is another room, and here is some data, so this could be like RAM, so let's say you're here. 59 00:04:27,730 --> 00:04:33,580 If you wanted to get something from RAM, it could be kind of analogous to going out of this room into 60 00:04:33,580 --> 00:04:35,380 another room and getting the data. 61 00:04:36,280 --> 00:04:42,940 If we want to compare that though, with getting something from the hard disk drive and I'm talking 62 00:04:42,940 --> 00:04:48,610 about like you being able to get some data for your program, you know, needing to fetch some data 63 00:04:48,610 --> 00:04:52,150 that's needed in your program that's running in that virtual address space. 64 00:04:52,720 --> 00:04:57,880 How far would you need to go when you're trying to get something from RAM compared to getting something 65 00:04:57,880 --> 00:04:58,780 from hard disk drive? 66 00:04:59,710 --> 00:05:02,440 So this is what it would be like on the hard disk drive. 67 00:05:02,770 --> 00:05:08,860 It would be analogous to you being here on planet Earth and you having to go all the way to Pluto to 68 00:05:08,860 --> 00:05:10,330 get the data and back. 69 00:05:12,470 --> 00:05:18,950 So it may seem kind of weird to say something like that, but really when you look at the numbers like 70 00:05:19,040 --> 00:05:25,100 how far away stuff is and RAM compared to how far away stuff is in the hard disk drive. 71 00:05:26,010 --> 00:05:29,880 It really is massive in terms of what the computer sees. 72 00:05:30,900 --> 00:05:34,510 So you might not notice that at all because everything seems really fast, right? 73 00:05:34,530 --> 00:05:41,070 Like you get stuff pretty much instantly from RAM and you pretty much get stuff instantly from the hard 74 00:05:41,070 --> 00:05:44,850 disk drive or the computer's moving really, really fast. 75 00:05:44,850 --> 00:05:47,910 And it's making like some really quick calculations. 76 00:05:48,480 --> 00:05:58,350 But if you look at the factor of like how much farther by what factor you need to multiply by to show 77 00:05:58,350 --> 00:06:02,580 the difference in distance between going to RAM and going to the hard disk drive. 78 00:06:03,700 --> 00:06:11,860 It would be something analogous to you having to physically go grab like pieces of paper that were data 79 00:06:12,160 --> 00:06:16,510 in another room and instead having to make a spaceship and go out to Pluto to get it. 80 00:06:17,200 --> 00:06:23,080 So pretty crazy and definitely really interesting when you think about the inner workings of the computer. 81 00:06:23,770 --> 00:06:30,610 Another reminder is that the hard disk drive is non-volatile, so thankfully we are able to save our 82 00:06:30,610 --> 00:06:36,460 documents and music and movies in a place that does not go away when the computer turns off. 83 00:06:39,770 --> 00:06:44,750 So another important thing about this virtual memory land is it has addresses. 84 00:06:44,990 --> 00:06:49,850 So imagine the virtual memory area as an incredibly huge parking lot. 85 00:06:51,120 --> 00:06:57,030 So this parking lot has a lot of different areas based on what type of cars are allowed to park there, 86 00:06:57,930 --> 00:07:04,170 and I'm using that analogy because there are different sections of memory that are kind of meant to 87 00:07:04,200 --> 00:07:05,680 handle different things. 88 00:07:06,960 --> 00:07:14,640 Each parking space in this parking lot is the same size and has a number associated with it so you can 89 00:07:14,640 --> 00:07:15,450 find your car. 90 00:07:15,900 --> 00:07:22,530 You can think of this as an address, and that is what we will be referring to these locations in the 91 00:07:22,530 --> 00:07:25,740 virtual memory space, as we would call them, addresses. 92 00:07:27,850 --> 00:07:34,990 So the memory addresses in this virtual memory land are represented in hexadecimal form, so you should 93 00:07:34,990 --> 00:07:37,960 be familiar with something like this, you've seen it before. 94 00:07:37,960 --> 00:07:43,810 We talked a little bit about binary and hex and decimal and octal and stuff like that. 95 00:07:45,070 --> 00:07:47,140 So here are some examples. 96 00:07:47,590 --> 00:07:53,180 So you see this number right here as high as zero X, that is actually not part of the address. 97 00:07:53,200 --> 00:07:56,410 This is just something you prepend to the address to tell you. 98 00:07:56,410 --> 00:07:59,200 It is Hex, so the zero x just means Hex. 99 00:07:59,800 --> 00:08:06,070 After it, you might see an h sometimes, but that's pretty rare in that also can mean hex like a lowercase 100 00:08:06,070 --> 00:08:06,400 h. 101 00:08:06,880 --> 00:08:08,350 People refer to it as that. 102 00:08:08,920 --> 00:08:15,760 So this cluding this right here we see one two three four five six seven eight f's. 103 00:08:16,510 --> 00:08:18,850 And here we see eight zeros. 104 00:08:20,270 --> 00:08:27,470 So basically, the zeros you can imagine as like in the very first parking spot. 105 00:08:27,800 --> 00:08:36,450 So at the very like, you know, this is the closest spot and the eight F's would be the highest number 106 00:08:36,450 --> 00:08:38,090 of spot, maybe like the farthest away. 107 00:08:38,990 --> 00:08:42,590 So this is the numbering system going from zero up to F. 108 00:08:42,590 --> 00:08:47,060 And that is, of course, because we're using the hex system, you know, where we're not just using 109 00:08:47,060 --> 00:08:51,770 numbers, we also have those letters being kind of the highest one in that base. 110 00:08:51,770 --> 00:08:53,960 16 Hex numbering system. 111 00:08:55,530 --> 00:09:01,800 And the reason that there are eight here is because. 112 00:09:02,940 --> 00:09:09,750 We are looking at something we could refer to as a 32 bit address space, so you might have heard of 113 00:09:09,750 --> 00:09:18,270 something about what your computer's operating system really is in terms of the architecture. 114 00:09:18,270 --> 00:09:25,020 So maybe when you look at details about your laptop or something like that or your desktop, you're 115 00:09:25,020 --> 00:09:29,010 looking at details about the OS, whether it be Windows or Mac or something like that. 116 00:09:29,640 --> 00:09:36,750 You might see like, Oh, I have 32 bit windows or I have 64 bit windows, and that's just talking about 117 00:09:36,750 --> 00:09:45,600 this type of operating system and also talking about the address space that you would have 32 or 64 118 00:09:45,600 --> 00:09:45,930 bit. 119 00:09:46,890 --> 00:09:54,810 So remember that we kind of used to hex characters to represent a bite. 120 00:09:55,200 --> 00:09:57,550 So each one could be four bits, right? 121 00:09:57,570 --> 00:09:58,950 Four bits here, four bits. 122 00:09:58,950 --> 00:10:00,210 They're eight bits. 123 00:10:00,210 --> 00:10:01,500 Make up a byte, right? 124 00:10:02,010 --> 00:10:07,350 And so if we kind of look at that here, here's eight eight bits, right? 125 00:10:09,150 --> 00:10:12,300 So if we said we had eight ifs here, right? 126 00:10:12,570 --> 00:10:19,650 So if we take this eight bits, which is a byte right here, you know, how many bytes do we have in 127 00:10:19,650 --> 00:10:19,890 here? 128 00:10:19,920 --> 00:10:21,540 Well, we have four of these, right? 129 00:10:21,930 --> 00:10:22,970 So here's one. 130 00:10:22,980 --> 00:10:25,170 You know, every two of them can be a byte. 131 00:10:25,180 --> 00:10:28,890 So we have one two three four. 132 00:10:29,430 --> 00:10:32,820 And so how many bytes are in here? 133 00:10:32,850 --> 00:10:33,240 Well. 134 00:10:35,240 --> 00:10:36,440 Or how many bits, sorry. 135 00:10:36,770 --> 00:10:39,530 It would be 32 bits, right? 136 00:10:40,160 --> 00:10:43,610 So we have four bytes or 32 bits. 137 00:10:44,450 --> 00:10:49,310 So you see these eight big chunks, eight times for thirty two, and that is synonymous with us talking 138 00:10:49,310 --> 00:10:50,990 about this 32 bit address space. 139 00:10:51,290 --> 00:10:56,600 You might also have seen you might be seeing your addresses in 64 bit. 140 00:10:57,770 --> 00:10:59,840 That can be kind of different. 141 00:11:00,560 --> 00:11:08,150 Sometimes they only show the, let's say, first 12 characters there. 142 00:11:09,470 --> 00:11:13,850 So that might be kind of confusing, but there could be like, you know, leaning chairs and stuff like 143 00:11:13,850 --> 00:11:14,150 that. 144 00:11:14,780 --> 00:11:19,310 But just wanted to use this 32 bit one to kind of help you understand it better. 145 00:11:21,990 --> 00:11:27,210 So this could be a theoretical piece of this virtual memory address land. 146 00:11:27,660 --> 00:11:31,050 And you can see that we are counting up in the addresses. 147 00:11:31,050 --> 00:11:32,970 So here are the parking spots. 148 00:11:33,210 --> 00:11:36,330 I mean, these would be like the places we could store our data, right? 149 00:11:37,020 --> 00:11:41,430 So you see it says one and two and three and four, and these are hex addresses. 150 00:11:41,430 --> 00:11:46,500 So it'll look a little something probably not exactly like this if you were to examine your computer 151 00:11:46,500 --> 00:11:48,840 memory, but something like this. 152 00:11:52,250 --> 00:11:59,300 So remember that these are represented in hexadecimal and they would start at like zero and go all the 153 00:11:59,300 --> 00:12:01,820 way up to all these efforts right here. 154 00:12:04,280 --> 00:12:07,370 So talk a little about that, a little bit about memory. 155 00:12:07,640 --> 00:12:13,790 But we should also talk a little bit about what we're going to get into in the next session, which 156 00:12:13,790 --> 00:12:14,750 is containers. 157 00:12:14,760 --> 00:12:16,610 So it's great and all that. 158 00:12:16,610 --> 00:12:22,610 We've been using variables like single variables, of course, you know, like making an integer or 159 00:12:22,610 --> 00:12:28,580 a float or something like that, but it limits us quite a bit to only be able to use single variables 160 00:12:28,580 --> 00:12:29,420 to store stuff. 161 00:12:29,900 --> 00:12:33,590 Wouldn't it be nice if we could store than one more than one piece of data? 162 00:12:33,590 --> 00:12:40,700 So like more than one end kind of in the same area, maybe we want to group a bunch of cars together 163 00:12:40,700 --> 00:12:44,150 moving forward with this analogy and park them right next to each other. 164 00:12:45,170 --> 00:12:52,070 So maybe we would want four cars parked right here next to each other in this virtual address space. 165 00:12:53,200 --> 00:12:59,800 So in the next few lectures, we're going to start using some basic containers where we can group our 166 00:12:59,800 --> 00:13:05,530 data and manipulate it so we can do more interesting things if you have a lot of your data stored in 167 00:13:05,530 --> 00:13:07,240 the same location. 168 00:13:07,480 --> 00:13:14,290 You can kind of combine that data in interesting ways and have a better type of organization of your 169 00:13:14,290 --> 00:13:14,890 program. 170 00:13:15,790 --> 00:13:19,390 It also makes it easier to write more complex programs. 171 00:13:21,430 --> 00:13:28,390 So with that, I'm going to leave you with this lecture, and we will then get into talking about these 172 00:13:28,390 --> 00:13:30,010 containers that I've talked about. 173 00:13:30,280 --> 00:13:36,580 If you are confused about the addressing when we go through the lecture again, or you could look up 174 00:13:36,580 --> 00:13:44,860 some additional information on how the address space works, we're going to be talking about how these 175 00:13:44,860 --> 00:13:53,350 containers kind of look in memory and where our stuff is stored in relation to the other stuff. 176 00:13:53,550 --> 00:13:56,560 When I say stuff, I mean, like variables like integers. 177 00:13:56,980 --> 00:13:59,750 Where is one integer compared to the next integer? 178 00:13:59,770 --> 00:14:03,220 How does it look if we put that in one of these containers that I'm talking about? 179 00:14:04,210 --> 00:14:04,540 All right. 180 00:14:04,540 --> 00:14:06,430 So with that, I will see you in the next lecture.