 It's very common that people fail to distinguish between what's called a monitor and an actual computer. A monitor is simply a display device. It's something which displays an image sent to it through a signal from the computer. Otherwise, a monitor is a dumb device. It's entirely up to the computer to determine what image to display. So try not to call your monitor a computer. Confusingly, however, there are examples where a monitor and a computer are housed together in one unit. Like, for example, Apple sells a line of computers called iMacs. And also, of course, a laptop is a system where the monitor and the computer have been housed together in one physical unit. If you look at the back of a desktop system, you'll see all sorts of connectors. So let's walk through them. First off, you should see a plug for a power cord, and next to it, a switch. This switch is not the power button, but it must be in the on position for your computer to have power. It's simply there as a convenience, so you can cut off power to the system without pulling out the cord. There are a few different kinds of monitor connections around right now, but today the most common is this connection called DVI. So most likely this is the connector for the cord that sends the image from your computer to your monitor. This connection below is an older kind of monitor connection called VGA. VGA is still around, but being phased out, so it's an example of what we call a legacy technology. On this particular computer, we happen to have outputs to send an image to a television. You probably recognize these from the back of televisions, VCRs, and DVD players. The one on top is called composite, and the one on the bottom is called S-video. And actually these are also examples of legacy technologies that are being phased out in favor of newer standards like, for example, HDMI. These two other connectors kind of look like S-video, but they actually have nothing to do with video. These are called PS2, and they're an old standard for connecting mice and keyboards introduced in the 80s. Most computers still have them, though they're hardly used anymore. The five plugs to the left here are mic jacks. Mic jack is used for audio, and in fact it's the same connector used for most headphones. The reason there's more than one is because two of these are input, like save for recording audio from a microphone, and the rest are for output. Only one output is needed for stereo, but for surround sound you need all three. This connector on the right, which looks like an oversized phone jack, is for Ethernet, which is the most common connection for wired networking. Most commonly, this is the port you use to get an internet connection. Finally, your computer should have some number of USB ports. Most computers have at least four, they're usually more like six or eight. And sometimes they have some USB ports not just in the back, but also in the front. USB stands for universal serial bus. It's universal in the sense that it's a connector for all sorts of different devices. Pretty much everything these days uses USB. In fact, the only thing which I can think of which isn't ever connected with USB is a monitor. Monitors require too much data to send over USB, so they have their own special connectors. But aside from that, pretty much everything else can use USB. In fact, even, say, speakers, which normally you would plug in via mic jacks, you can get speakers which connect via USB. And also for networking, rather than using Ethernet, it's possible to use USB. Now, not only is USB designed to be pretty much universal, it has a few neat features. Like, say, power can be supplied over USB cables. So in fact, many small devices can be charged by connecting them via USB to computer. Like, for example, that's how I charge my cell phone. Another neat feature of USB is that it's designed to be hot-plugable. Hot-plugable means that you can connect things and disconnect things while the system is actually running. With some other connection types, you're not allowed to do that, or at least it's considered a bad idea. And so, inconveniently, you have to turn off the system to connect or disconnect things. USB makes that unnecessary. Lastly, USB has this neat feature called chainable hubs. The idea of a hub is that it's a USB device into which you can plug other USB devices. Here, pictured in the bottom right, is a USB hub with four ports. And so, you plug that into your system through a USB port on the computer, and then you can plug in four other USB devices through that one hub. And this can be really convenient. First off, it means that if your computer only has one or two USB ports, as, like, say, many laptops tend to have, you're not limited to the number of ports on your system. You can use a hub to expand effectively the number of ports. Hubs also can come in handy because they, in effect, can act like extension cords. So, for example, if, say, the cords of your mouse and keyboard aren't quite comfortably reaching your computer system, you can solve the problem by using a hub. In fact, it's very common for monitors to have a USB hub built-in, so you will have a USB connection running from your computer to your monitor, and then on the side of it, your monitor, you'll have some number of USB ports into which you can plug any device in, like your keyboard or mouse.