 When we talk about computers these days, we're usually referring to what's called a PC, a personal computer. A computer that comes in basically one of two configurations, a desktop or a laptop system. A desktop is a non-portable system where the actual screen, the display, the monitor, is a separate unit from the computer itself, which is usually this small tower. In a laptop system, the monitor and the computer itself are put together in one portable unit, and whereas with a desktop, the keyboard and the pointing device, the mouse, are attached to the accords to the computer, in a laptop, the keyboard and the pointing device, a trackpad, are built on to the computer itself. So it's all one physical portable unit. The term hardware simply refers to any physical component of a computer system. If you can hold it in your hand, it's hardware. Software, in contrast, is not physical. Software is simply the instructions which are executed by the computer. What we call a program is just a piece of software. It's some set of instructions for some coherent purpose. Programs can be written to do all sorts of things, but here's the list of what are probably the nine most commonly used types of programs today. First off, a word processor is simply a program for creating and editing textual documents. A spreadsheet is a program mostly used in business. It presents the user with a grid of rows and columns into which the user can plug data, and then the user can have the spreadsheet perform calculations upon these rows and columns, and also do things like, say, draw charts from this data. When people talk about using the internet, what they're usually really talking about is using a web browser. A web browser displays web pages, which are textual and graphical documents which are retrieved from other computers out there on the internet. By far, web browsing has become the most popular thing to do with a computer. Web browsing probably now takes up over 90% of the time people spend using computers. An email client is a program you use to send and receive email. An email, very simply, is a textual message you send to another user on the internet. An instant messenger is also a program you can use to send textual messages to other people on the internet, but it works a bit differently. Email is like sending a letter. You send it off, and then it sits in the recipient's mailbox until they check their mailbox. With instant messaging, it's expected that the recipient is also running an instant messenger at the time you send the message, and the message then instantly appears in their instant messenger program. The message doesn't sit and wait in a mailbox until they check it later. With most instant messengers, you can't send a message to someone who isn't currently running their instant messenger program. So instant messaging, or I-M-ing, as it's called, is more appropriate for immediate conversations. It's more like a chat room, except the messages are still private, like with email. They only get sent to one recipient. A media player, unsurprisingly, is a program for playing media, and when we say media we mean mainly video and audio. So say if you put a DVD in your computer and wish to play it, you use a media player to do so. An image editor, of course, is a program for creating and manipulating digital images. By far the most popular program for this purpose is a program called Photoshop. In fact, Photoshop has been so popular for so long that the word Photoshop has become synonymous with manipulating digital images. So you'll commonly hear people talk about photoshopping an image to mean digitally manipulating that image. Most video these days is now digital, and so it's edited on computers using programs called video editors. Even stuff that's still shot on film these days is edited with video editing software, because it's just that much easier to do it on a computer rather than having to deal with all this physical film. And finally, the last type of program to mention, games. And games, of course, run the gamut from the very early video games like Pac-Man and Pong, to simple card games like Solitaire, and then today's modern games with complicated 3D graphics. Actually, there's one more important type of program to talk about, and that's what's called an operating system. An operating system is a very different kind of program because it's not one you use to accomplish any particular task. It's a program you use to run other programs. It's the operating system in a modern computer which allows it to run multiple programs at once. When you power on your computer, the first thing it does is it loads the operating system which you have installed on that system. Once the operating system has loaded, you can then use its interface to launch other programs. For the last two decades, the most popular operating system to run on PCs has been Microsoft Windows. The latest version of which is called Windows 7, and that was released in 2009. The version before that was called Windows Vista, and the version before that was called Windows XP. Here in 2010, you should be at least using Windows Vista if not Windows 7. A lot of people are still running Windows XP even though they really shouldn't. For reasons I'll explain later having to do with security, you generally shouldn't run very old software. The two main alternatives to Windows are an operating system called Linux, and Apple's operating system called Mac OS X. Linux is interesting because it's an example of what's called free or open source software, meaning that anyone is legally allowed to use, copy, and modify the software. So as a user, that means you don't have to pay for it. Only about 2% or so of users worldwide use Linux on their PC, but Linux otherwise is a very successful piece of software because it's used in all sorts of other devices, like probably your car or your cell phone or your toaster or your cable box or your Tivo. Tons and tons of stuff out there runs Linux, even though it's not very popular on PCs. Mac OS X, in contrast, has become increasingly popular in the last 10 years, and now it accounts for maybe 10% of PCs, at least in the United States. OS X is certainly not free, and in fact Apple only wants you to run OS X on computers which you buy from them. Even though the hardware which Apple sells internally isn't really any different than what you can buy, say, from Dell. The cases are different, and they make their own keyboards and mice, but otherwise it's just the same stuff. However, to stop people from running OS X on hardware which they themselves do not sell, Apple put a check into OS X such that when it loads, it looks for this specific chip, and if your hardware doesn't have this chip, which only Apple sells, OS X will not load. So just be clear what you're paying for when you buy an Apple computer. Apple charges a 30-50% premium for the same hardware you can buy from other computer makers, but people pay it because they like Apple's nice shiny case design, but most importantly because they want to run OS X, and the only way they can do it is by buying their computer from Apple. Now whether you use Windows or Linux or Mac OS X, the user interface is generally about the same in each of them. Many details differ, but the big ideas are really just the same. So while the material I'm about to cover is a bit biased towards Windows, it's for the most part applicable to all three different operating systems.