WEBVTT 00:00.360 --> 00:10.800 You may be familiar with computers as devices that store a collection of programs like files or graphics. 00:11.720 --> 00:18.840 Right now in this lecture, we will shift our perspectives to something different here. 00:19.360 --> 00:25.920 We will look at computers as billions of two state switches. 00:29.360 --> 00:31.560 Consider this as light switches. 00:32.280 --> 00:33.200 These are the. 00:33.800 --> 00:38.240 This means off and on right. 00:40.560 --> 00:49.320 We will look at computers as billions of two state switches managed by the control unit. 00:49.400 --> 00:50.160 Control unit. 00:50.160 --> 00:56.440 In this case, let's say it's you that controls this right now. 00:56.440 --> 01:03.300 In the previous lecture, we explored how computers communicate with the outside World using the input 01:03.740 --> 01:05.740 and output systems. 01:05.940 --> 01:10.060 Now we will investigate how computers encode. 01:15.340 --> 01:17.900 And store data in memory. 01:17.900 --> 01:25.140 And we will write a C programs to reinforce these concepts in next lecture. 01:27.180 --> 01:36.940 Everything your computer does from streaming a video, uh, to compiling a code like this, relies on 01:36.940 --> 01:47.020 a billions of two state switches working together to make some sensible data, right? 01:47.220 --> 01:51.220 Each unique configuration of switches represents a specific state. 01:51.740 --> 01:54.820 Describing this state in a plain language will be tedious. 01:54.980 --> 02:04.800 So instead we use the numeric representations instead of writing like on or off. 02:05.080 --> 02:10.120 But you will see on or off representations of one and zero. 02:11.480 --> 02:19.080 In some examples, basically, uh, on here is one and off here is zero. 02:19.240 --> 02:21.600 It's like a light bulb. 02:21.760 --> 02:24.080 So this is a light bulb. 02:24.800 --> 02:27.160 Sorry for my drawing skills here. 02:27.160 --> 02:30.000 So light bulb does not have a light. 02:30.000 --> 02:32.520 So this is off. 02:34.240 --> 02:40.200 And if the light bulb is on then it shines right. 02:42.520 --> 02:45.720 So this is basically on right. 02:46.440 --> 02:50.040 This has the same, uh, logic. 02:55.120 --> 03:04.300 And at the core of every computer, there are billions of microscopic switches called tran Resistors. 03:08.500 --> 03:16.980 Now, each transistor can exist in one of two states, on or off. 03:17.220 --> 03:17.780 Right. 03:19.300 --> 03:26.940 Which on means electrical current is flowing off means it's not. 03:30.060 --> 03:35.460 And these two states represents the most basic form of information. 03:35.820 --> 03:39.220 The ones or zeros. 03:39.820 --> 03:43.260 This is why computers use the binary system. 03:43.300 --> 03:45.540 Now we call it the binary. 03:51.100 --> 03:51.740 And now. 03:57.420 --> 04:01.620 How we write binary is to make it more understandable. 04:03.220 --> 04:04.240 For example 04:05.680 --> 04:08.240 1101. 04:09.080 --> 04:10.440 Now this is a binary number. 04:11.880 --> 04:19.360 Each activity you perform on a computer, whether it's a playing a song, writing a document, or browsing 04:19.360 --> 04:27.400 a website, this boils down to manipulating combinations of ones and zeros, right? 04:28.320 --> 04:30.840 Now what is a bit you may ask? 04:30.960 --> 04:32.040 Now a bit. 04:32.480 --> 04:36.920 A bit is the smallest unit of data in a computer. 04:36.960 --> 04:42.440 Now the word bit comes from binary. 04:49.560 --> 04:50.200 Digit. 04:53.560 --> 05:00.440 It be and bit the word from binary. 05:01.000 --> 05:12.050 The bit comes from binary digit a bit as I explained, can be one which is on or zero which is off. 05:12.210 --> 05:16.610 However, a single bit is too small to represent useful information. 05:16.850 --> 05:24.250 So computers group bits together to make some sensible information that makes sense, right? 05:25.890 --> 05:27.370 So eight bits. 05:29.610 --> 05:32.130 Equals one byte. 05:35.410 --> 05:35.810 Right. 05:36.170 --> 05:40.250 Now a byte is big enough to store one character. 05:40.290 --> 05:41.250 Oops, sorry. 05:41.690 --> 05:45.450 Yeah, a byte is big enough to store one character. 05:46.250 --> 05:47.730 Can you see the screen? 05:47.770 --> 05:48.090 Yeah. 05:48.130 --> 05:49.010 That's perfect. 05:50.170 --> 05:51.730 So we can store. 05:54.050 --> 05:57.690 Characters inside eight bits, which is one byte. 05:58.530 --> 05:59.010 So what? 05:59.330 --> 06:00.410 What can we store? 06:00.450 --> 06:01.610 For example, a. 06:01.890 --> 06:06.990 We can store single A, single B Or like single. 06:07.030 --> 06:10.510 See the question mark. 06:10.870 --> 06:11.270 Right. 06:16.310 --> 06:20.910 And the pattern of eight bits in Ascii representation. 06:26.110 --> 06:27.190 Of the letter A. 06:28.750 --> 06:32.390 How can we do that is a. 06:32.430 --> 06:38.190 Here is 0100 06:39.310 --> 06:46.070 half byte and 0001. 06:46.630 --> 06:47.350 So we will. 06:48.710 --> 06:58.270 It's always advisable to write bits and bytes in a for format. 06:59.870 --> 07:01.910 And yeah that's basically it. 07:02.270 --> 07:08.690 Uh this is a in a binary representation in Ascii. 07:12.210 --> 07:13.250 Representation here. 07:14.170 --> 07:16.530 So why computers use binary at all? 07:19.650 --> 07:24.650 Now, binary is ideal for electronics because it is simple and stable. 07:25.730 --> 07:28.010 Now there is a three main reasons here. 07:28.210 --> 07:30.170 The first is. 07:35.530 --> 07:37.050 Electrical efficiency. 07:45.850 --> 07:49.130 Two voltage levels like zero volts. 07:55.250 --> 07:56.650 And five volts. 08:03.010 --> 08:06.170 Are easier to distinguish than ten different levels. 08:06.170 --> 08:06.690 Right. 08:06.910 --> 08:10.270 or so, 0.5V. 08:10.310 --> 08:10.550 Yeah. 08:10.550 --> 08:16.670 This is another form of information which you will learn later. 08:17.270 --> 08:19.590 But yeah, that's basically it is efficient. 08:19.830 --> 08:32.070 Or it could be like 0V or 3V or 1.3V, which I, I strongly believe that if you have got into your Bios 08:32.070 --> 08:32.750 settings. 08:35.590 --> 08:38.830 There's a choice that you can make. 08:39.070 --> 08:44.950 Um, the options on the 1.3V or three volts. 08:46.150 --> 08:52.070 And yeah, that's basically the most efficient as computers get right now. 08:53.590 --> 08:55.790 And it has error resistance. 09:07.970 --> 09:11.650 So binary signals are less likely to be corrupted. 09:11.650 --> 09:16.810 It is either zero volts or some volts, like 3V or 5V. 09:16.850 --> 09:17.290 Right. 09:17.970 --> 09:18.930 And it is simple. 09:23.530 --> 09:28.930 So circuits built for two state logic are more reliable and easier to design. 09:29.290 --> 09:33.090 Now, as humans you know that we use decimal. 09:34.170 --> 09:34.930 Decimal. 09:35.650 --> 09:36.170 Yes. 09:41.610 --> 09:46.890 So if you don't know what decimal is, decimal is the basically base ten. 09:49.090 --> 09:52.410 Base ten, which we use like ten. 09:52.450 --> 09:52.970 Right. 09:53.010 --> 10:01.930 Or 296 or 300 90 or 1005. 10:01.970 --> 10:02.530 Right. 10:02.570 --> 10:06.090 This is our number system that humans use. 10:06.610 --> 10:18.510 But binary which is base two, is perfectly suited for hardware, so all modern digital computers use 10:18.510 --> 10:20.150 binary under the hood. 10:22.750 --> 10:32.630 And there's another nice thing we have which represented large binary numbers in hexadecimal notation. 10:33.070 --> 10:41.270 And as you have seen so far, binaries, binary numbers can get very long very quickly. 10:41.270 --> 10:41.710 Right. 10:42.030 --> 10:44.790 So for example zero or. 10:48.830 --> 10:59.870 110101101010 11:00.590 --> 11:03.950 and 0111. 11:04.230 --> 11:15.210 Now this might look much but compared this is basically means two war two characters in Ascii here. 11:16.050 --> 11:19.170 Now this is hard to read and prone to mistakes. 11:19.490 --> 11:28.170 And that's where hexadecimal helps the hexadecimal, which is let's say the hexadecimal. 11:31.330 --> 11:33.250 Hexa decimal. 11:36.530 --> 11:37.490 Or hex. 11:40.530 --> 11:42.730 Is a base 16. 11:46.170 --> 11:51.490 16 number systems, so it uses digits from zero. 11:51.690 --> 11:53.130 I will also take notice. 11:53.810 --> 11:58.810 So from 0 to 9 and letters from A to F. 12:02.010 --> 12:04.650 Or uppercase A to f. 12:04.650 --> 12:07.410 So uppercase and lowercase doesn't matter here. 12:07.410 --> 12:09.130 So you can write both ways. 12:09.490 --> 12:13.030 It is either uppercase or lowercase. 12:13.750 --> 12:23.110 In computer language, it doesn't matter at all, and one hex digit can represents four binary digits. 12:23.510 --> 12:24.950 So here. 12:28.950 --> 12:30.310 This is basically. 12:32.710 --> 12:33.790 A one hex. 12:34.590 --> 12:41.470 So as I said one hex character can represent four binary digits. 12:42.430 --> 12:44.870 In this case it is four hex right. 12:46.030 --> 12:49.670 In this case it is four hex. 12:50.230 --> 12:57.430 So each one is one hex hexadecimal one hexadecimal. 13:00.430 --> 13:04.470 One hexadecimal and one hexadecimal. 13:07.870 --> 13:09.830 So why use hex at all? 13:10.480 --> 13:18.640 Hex has you have seen so far, is easier to read, has a shorter representation, and it is common in 13:18.640 --> 13:22.160 debugging and programming, as you will see in next lectures. 13:23.280 --> 13:35.440 So basically this binary here 1101 we'll use different color means be in Ascii. 13:37.960 --> 13:43.720 And for example 0110 is. 13:45.800 --> 13:46.400 Six. 13:50.680 --> 13:55.040 And 1010 is a. 13:57.720 --> 13:58.080 A. 14:02.280 --> 14:04.480 Or yeah we can write uppercase. 14:05.720 --> 14:12.940 And yeah we have 10111 is seven. 14:14.580 --> 14:16.940 By the way, don't miss. 14:16.980 --> 14:18.500 Don't make mistakes here. 14:19.020 --> 14:20.820 These are all hex. 14:24.660 --> 14:25.300 Hex. 14:25.340 --> 14:27.460 This is not a word here. 14:27.980 --> 14:30.580 This is a hexadecimal representation, right? 14:30.820 --> 14:32.300 And this is a number. 14:32.300 --> 14:34.060 This is a hexadecimal representation. 14:34.340 --> 14:36.060 Don't make a mistake here. 14:36.060 --> 14:38.900 This is hex two and this is hex two. 14:40.300 --> 14:48.900 So if you see £0.07 in debugger, what does this mean? 14:49.540 --> 14:56.380 Seven b means translates to 70111. 14:57.340 --> 15:02.100 And B is 1101. 15:02.460 --> 15:04.540 Yeah that's not so hard right. 15:05.340 --> 15:20.920 And also for example b6 here translates into b P is 1101 and 0110. 15:21.400 --> 15:26.640 Or for example, six seven translates into. 15:29.120 --> 15:29.720 What? 15:33.440 --> 15:34.960 Six seven translates into. 15:35.000 --> 15:46.440 Yeah zero one, one zero and seven here 0111. 15:49.600 --> 15:51.240 So these are not words. 15:51.920 --> 15:56.760 I will remind you, these are just the hexadecimal representation of bits here. 16:02.720 --> 16:09.920 And you can use the tools like calculator applications or online converters to help while learning this.