Hi everyone. Welcome to this section called "Computers architecture and networks". This is the fourth part about computer sciences and its foundations. This part will be divided into four sequences, and the first one will look into the elementary components of a computer. To describe these components, I will use a video that you will be able to find in the digital section of this MOOk, a video called "Disassembling of a computer". In that video, you will witness Erwan dismantling the computer completely and you will have access to plans such as this one, where the motherboard can be seen at the bottom of the computer and on which the processor can be found. The processor is the core element of the computer. That's where all the processing is done. By processing, I mean all the calculations, addition, multiplication, etc., but also comparisons or memory access, which Sylvie talked about it earlier. All calculations are performed in the processor. It really is the machine's heart. You can find them in all modern objects carrying some kind of computing capacities, like computers, smartphones, televisions, etc. What can the processor do? It can read and write data in the memory, and also perform operations on it, operations on bits, on numbers, additions, multiplications, comparisons, etc. Technically, it can do many things. Modern processors can perform several billions of operations per second. But those operations are very simple, additions and multiplications, things like that, not complex operations, it is not intelligent. It will do very simple things, but it will do them very well and very fast. When performing calculations, it manipulates data. Technically, it will have to perform operations by entering data and an outgoing result. If you ask it to add 2 and 3, it's going to have to search for 2 and 3 in the memory and write the addition's result, 5, in the memory. The question is: where is that data stored? Generally, the data, when launching the program, are stored on the hard drive. For example, an image you want to display on the screen, some text you want to modify, a program you want to launch that needs to be loaded and executed in the processor. After executing the program, the result will generally be saved on the hard drive, whether it is an image that was modified by a retouching software, a text file that has been modified, etc. So technically, there are lots of exchanges happening between the processor and the hard drive that stores information at the beginning and the end of the program. That's the hard drive on Erwan's video. At first, the drives were located in slots at the bottom of the machine, where the bottom arrow is pointing. Erwan disassembled them and placed them on the top left and on the right. You can see they are connected by a blue wire, connected to the motherboard, linking them to the processor. Data exchanges between the processor and the hard drives happen through those wires. If data transfers happen between the processor and the hard drive, what is the memory for? The computer's memory is located between the processor and the hard drive. That's because the hard drive is very slow. I told you the processor performed billions of operations per second.The hard drive can't keep up the pace. It is much slower that that, which means the processor will have to wait for the hard drive to send it the data before being able to perform those operations. So the memory is going to be in the middle,the RAM memory, Random Access Memory, that will act as a mediator. Data is going to be loaded in the memory.The processor will use it to perform operations. When it's done, the result will eventually be sent back to the hard drive if some data needs to be saved. Memory is designed to be a temporary storage area, transitional, which will be smaller than the hard drive. Only the things we need will be stored inside. Things will be stored temporarily while the processor is using them. On the contrary, a lot of things can be stored on the hard drive, but they can't be reached as fast. so, memory is different from the hard drive because the processor can access the memory directly, whereas it can't access the hard drive directly. That's not the main reason. The main reason is really that the hard drive is too slow to feed the processor with operations. In Erwan's video, memory is located in the upper part. Those are small clips that are inserted into the motherboard to add a certain amount of memory. Data exchanges are going to take place mainly between the processor and the memory. The processor is going to read the incoming data, work on it, and store the result as an output. From time to time, there will be data exchanges between the memory and the hard drive, particularly when launching programs when the program and the data, the files it has to open will be read and stored in the memory. When closing the program, if things have been modified, the result in the memory will be saved on the hard drive. That's mostly what happens inside a computer. We also have to take a look at how the computer communicates with the outside, particularly how it interacts with the user and also how it interacts with other computers. For that purpose, there are peripheral devices that are connected to the processor and the memory. There are many of them. Regarding the output, meaning everything that will be sent to the outside from the computer, there is the screen, the printer, loudspeakers, etc. Regarding the input, when we are giving instructions or information to the computer, there is the mouse, the keyboard, sensors, cameras, etc. There is also what we call network cards that can be wired when plugging a wire inside, wifi, and all antenna communication types like 3G, 4G, which are also peripherals allowing to get information in and out of the computer. The processor has all those peripherals the memory and the hard drive. It will read and write in all those various peripherals, according to what it is asked to do. Most peripherals on a computer correspond to ports located inside the machine, on the back generally. In this video extract, we can see the video outputs, here is DVI, in white, on the right of the video. We have the network output as an RJ45 type. Those are common network cables, allowing the computer to connect to the internet. There are also a certain number of less common ports, such as PS2 ports to connect old keyboards and mouses, serial ports and parallels, which are not used very much anymore nowadays. Today, instead of using those PS2 and serial-parallel ports, we essentially use USB located on the upper left, this allows you to connect anything and everything, mostly keyboards and mouses, but also many things like printers, etc. Now let's talk a bit about smartphones, which are also computers, but very different from the outside, not only because of their size but also because instead of having lots of ports like a computer, it is going to have lots of peripherals, but integrated inside the smartphone. It may not be obvious, but smartphone screens are touch-sensitive. The touch screen will replace the keyboard we usually have on a computer. On smartphones, there is a small keyboard made of a few buttons, but the rest of the keyboard is integrated into the touch screen. There is a loudspeaker, a mike, etc. There are many other things that may be less visible, like the camera, a proximity sensor allowing the smartphone to know whether we are calling with the phone next to our ear or not, and many internal things like gyroscopes, accelerometers, vibrators, things like that, a lot of sensors allowing it to gather much information about its environment and hand it to the processor which will make calculations. What do you need to remember about this section? First, it is very important to understand that the processor performs all the processing. It is the machine's heart. Without it, not much could be done. Technically, it is going to use data stored mainly in the memory. Where does this data come from? It can come from the hard drive. Most often it is the case. It can also come from input peripherals, whether it is the network card we are receiving by network communication, if we connect to a server through a browser, or with the mouse when clicking. The application's results, so the output data, will also often go to the hard drive or eventually to an output peripheral, like the network card if we are sending data on a distant server or all other output peripherals like the screen, the printer, etc.