 So, first off, the central concept in the user interface of all of these operating systems is that of a window, which is in fact why Microsoft calls their operating system Windows. The point of a window is that in a modern operating system, we want the ability to run multiple programs at once, and what that means is when you have multiple programs running, each program can't monopolize the entire screen, they need to share screen space. And so the idea is that each program is presented on the screen as its own box, a window. And that window you can move around and the windows can overlap each other and you can resize the windows to your liking. And each window has three basic components. You have at the top, you have the title bar where it says the name of the program, you have a border around the window, and then you have the content pane, the space where the actual program interface is displayed. So whatever the program wishes to show the user, it gets displayed in the content pane. To interact with these windows, users need a pointing device, and on desktop PCs, that's going to be a mouse. What the user is currently pointing at on screen is represented by a cursor, which is usually just a little arrow, and they move the cursor around by moving their mouse around on the desk. And the typical mouse these days has three buttons, a left button, a right button and the middle button. And the middle button on most mice these days doubles as a scroll wheel. So you could push it in to click that button, or you can actually roll the wheel up and down. By far the most important button is the left mouse button, it's the one you'll be clicking the most. And if you're right handed, you should be clicking it with your index finger. If you're left handed, most mice you can configure so that the buttons are swapped. So what we call the left mouse button is actually the right mouse button. So that's something you may want to do if you're going to be moving the mouse with your left hand. A lot of left handed users just get used to using the mouse with their right hand, or they simply just learn to click with their ring finger rather than their index finger. In any case, what clicking the left mouse button actually does is really up to what is under the cursor on the screen. When the cursor is over something on the screen, which looks like a pressable button, clicking the left mouse button should press that button. For many other things, when you click the left mouse button, what it does is it selects that thing underneath the cursor. And in other cases, clicking the left mouse button simply will change the focus, what's called keyboard focus, to the thing which you click on. And by giving a thing keyboard focus, it means that when you type keys on the keyboard, those keystrokes apply to the thing that's been given focus. For example, when you wish to use the keyboard to interact with a window, you need to make sure that window first has keyboard focus, otherwise your keystrokes aren't going to apply to that window. Some things on screen can be interacted with by clicking and dragging them. To click and drag simply means to click the left mouse button, but hold it down, then move the mouse, and then release the left mouse button. So for example, the thing we use click and drag the most for is to move our windows around, and then also to resize them to make them bigger or smaller. So here I have this single window. I click on its title bar and hold the mouse button down as I move the mouse around. I let go and the window's repositioned. If I then click and drag on the border of the window, I can resize the window. And notice that it matters which edge of the window I click. If I click on the top edge, I can only move the top up and down. If I click on one of the corners, I can move that corner in and out and so forth. Now, if you look at the screen in Microsoft Windows, you'll notice usually at the bottom of the screen, there's this thing we call the task bar. And on the right side of the task bar, you should see a display of the current time. And on the left side of the task bar, you should see a button which you can click to open what's called the start menu. In earlier versions of Windows, this button was actually labeled start, but in more recent versions in Windows Vista and Windows 7, it's just a Windows icon. As we'll get into later, the start menu is what you use to start programs. For now, we're just going to look at the task bar itself. The idea of the task bar is that for every window you have open, there's a button representing that window on the task bar. So here because we have a Microsoft Word window and a Photoshop window, there are buttons on the task bar representing each of them. When you click on the window itself, you bring that window forward and you give it keyboard focus. But another way to do this is not by clicking on the window itself, but by clicking on the button that represents that window on the task bar. This alternative method of bringing a window forward is very important because sometimes you might have a window which is totally obscured by other windows, so there's no way you can click on it. You need to go to the task bar to click on its button to bring it forward. The area of the screen which is not the task bar and which is behind the windows is called the desktop surface, or just simply called the desktop. Rather than leaving this as just a boring blank solid color, a lot of people like to put an image on their desktop, what's called a wallpaper, and on the desktop itself, but behind all of the windows, you might have some number of icons. These icons, as we'll discuss in the next unit, are really just files. But for now, we won't say anything more about files, icons, or the desktop. In the top right of every program window, you should see these three buttons in this order. On the left, there's the minimize button, in the middle, there's the maximize, de-maximize button, and on the right, there's a close button. The close button, not surprisingly, closes the window. It gets rid of the window and it exits the program and makes the program stop running. The maximize window puts the window into a special state where it covers the whole desktop area and it's on top of all the other windows. To get it out of the state so that it's a resizable and movable window again, you have to then click the same middle button to de-maximize the window. Finally, to minimize a window means to hide the window such that the only way to get it back to make it reappear is to click on its button on the task bar. Here I click the minimize button, the window goes away, I go down to the task bar to click its button and it reappears. I hit the maximize button and now it's taking up the whole screen area except for the task bar. I click the button again and it restores back to a regular window which I can move around. If I hit the close button, the window then goes away and here I click the close button on this other window and it goes away too. So far when we've talked about windows, we've assumed that each window is its own separate program. But that's not always necessarily the case. In many programs you have these secondary windows called pop-ups or dialogues. The general idea of a pop-up dialogue is that it's a temporary window. It's a window which the user is meant to interact with and then hit OK or cancel to get rid of. So here for example in Microsoft Word, when I click the button for configuring the page setup, the margins and the size of the paper and so forth, I get this dialogue window which has all of those options and I need to specify the configuration I want and then when I'm done and have everything the way I want, I hit OK and then the window will go away. If however I change my mind and decide I don't want to make any changes to the page setup, I can hit cancel and the dialogue will go away without changing anything. Here's another example. This program is displaying a document and if I click this button here to print the document, I get this pop-up dialogue and the window contains all sorts of complicated options about how I want to print the document and then there's a button for OK and a button for cancel. If I were to click OK, the document would then print with all of these options. If I were to hit cancel, it would just cancel the whole printing and the dialogue would go away. Notice what happens though with this dialogue. When I try and click on the main window, when I try and do that, when I try and interact with the main window again, it doesn't let me because the dialogue is still open. So dialogues very often do this. They block any interaction with the main window. So you have to get rid of the window by either hitting OK or cancel. And note that this dialogue has the big red X close button in the top right. If you click that, it's the same thing as clicking cancel. Dialogues come in varying degrees of complexity. Like say in the top right here, a fairly complicated one is this dialogue for opening a file. And very commonly, you'll see simple dialogues like this, which are simply asking us to confirm if we really want to do something. In this case, do I really want to delete this file? Yes or no? And then annoyingly, sometimes you get these dialogue windows which don't want to ask you anything. They just want to tell you something. And you have to hit OK to make them go away. And dialogue windows of all kinds tend to be annoying to users for basically two reasons. The first is they very often block interaction with the main window. And the second reason they can be annoying is because it's very easy for these little dialogue windows to get lost behind other windows. And unlike with program windows, these dialogue windows don't usually have a button representing them in the task bar. So if they get lost behind other windows, the user might not even be aware that the dialogue window is there. Finally, we should be clear that there are cases where a single program is made up of multiple windows. And those other windows aren't necessarily dialogues, because you're not meant to interact with them and then hit OK or cancel. Like here, for example, in this image editing program, you have the window with the image itself, and then we have this separate window with all these little tools we can use to manipulate the image. The designers of this program could have simply put these things together in one window, but they decided that users would want the flexibility to position these things separately, so they made them separate windows.