 There are many different types of storage devices, but here are pictures of the three most commonly used today. On the left is a picture of a hard drive. A hard drive is about the size of a large paperback book or maybe a deck of cards, and it's usually placed on the inside of your computer. Hard drives are generally your highest capacity storage option. Today, here in 2010, you can buy a hard drive for about $100 that has about a terabyte, which is 1,000 gigabytes, which is probably more storage than you'll ever need. In the top right corner here is a picture of what's sometimes called a flash drive or a thumb drive. These things are very small, about the size of a stick of gum or smaller, and this one here can store 16 gigabytes. And these things are handy because it's a decent amount of storage you can carry around with you, like say put it on your keychain. In the bottom right here is a DVD drive, and these drives can read the DVDs that you rent from the video store, and also they can read DVDs with any kind of data stored on them. It doesn't necessarily have to be video. A single DVD can store a little under 5 gigabytes. The problem with DVDs though is you can't write to them in the same way that you can write data to a hard drive or to a flash drive. Most DVDs are actually created in a mass printing process in a factory, and the data on these disks can't be erased or changed. However, you can buy blank DVDs, which you can actually write to. The problem still though is that writing to these DVDs is really very slow and cumbersome, and most blank DVDs can only be written to once. Once you've written something on the disk, it can't be erased. So if you have some data which you want to archive, putting it on a DVD might be an OK solution, but it's generally not the sort of medium you write to on a casual basis. Especially in the case where you have some data that changes frequently, you're going to want to store that on a hard drive or flash drive, not a DVD. Now in a typical computer system you have at least one hard drive and one DVD drive, but you might have some number of additional hard drives, maybe some additional DVD drives, and then also some number of flash drives plugged in. And so in Windows we need some way to distinguish between these drives, and what Windows does is it assigns each drive its own letter. And when written, these drive letters are usually followed by a colon. So for example, on a system I might have a C drive, a D drive, an E drive, an F drive, and so forth. Now when we store data on a drive, we do so in units called files. Files come in all sizes, from a handful of bytes all the way up to some number of gigabytes. Each file has a name, and to keep things more organized, files are divided into directories, which are also called folders. Like files, directories themselves have names, and a directory is simply a list of the names of files and other directories contained within it. So because directories can contain other directories, what you get in effect on a drive is a hierarchy of directories. At the top of this hierarchy, you always have a special directory which doesn't have a name, but which is called the root directory. Effectively, all of the files and directories on a drive are contained within this root directory. So for example, imagine I have a storage drive which Windows has assigned the letter C. Here we have a diagram of its directory structure. At the top of the hierarchy is the root directory, and inside that directory are two other directories, one called music, the other called pictures. And then inside the music directory itself are two other directories, one called Beatles, Dash, Sergeant Pepper's Lonely Hearts Club Band, and the other called Talking Heads, Dash, Stop Making Sense. If we list the contents of a directory, we should see the directories contained directly within it and also any files in that directory. So in this example, when we look at the root directory itself, you will see inside it are two directories, one named music, the other named pictures, and it happens to have also a file called business receipts.xlsx. For another example, if we look inside the directory called Beatles, Sergeant Pepper's Lonely Hearts Club Band, then we see these 13 files, each one of which is an audio file. It's a track from the album. To uniquely identify any directory or file on your system, you can write what's called a file path. A file path includes, in order, the drive letter, and then all of the directories in which the thing is contained, and then the thing itself, the directory or the file. And these components of the file path are all separated by a backslash. So for example, the file path to the directory Beatles Sergeant Pepper's Lonely Hearts Club Band is written as C colon slash music slash Beatles dash Sergeant Pepper's Lonely Hearts Club Band. And because this is a path to a directory, we end with another backslash. The path to a file within that directory is written the same, but with the name of the file at the end, and notice it doesn't end in a backslash because this is a file, not a directory. When it comes to these file paths, Windows is actually not all that picky. First off, you don't necessarily have to use backslashes. Windows is perfectly happy if you use forward slashes instead. Also, for a path to a directory, the convention is that it should end in a slash to designate that this is a directory and not a file, but it's actually okay if you omit the slash. Also, when you name your files and directories, Windows keeps track of which letter cases you use, say whether you use an uppercase W or a lowercase W, but then when you write a path, Windows doesn't care if you use uppercase or lowercase. So here the path C colon slash Windows with an uppercase O W and S at the end is actually the same path as the ones above it. Because of this laxness in paths about letter case, you can't in a directory have two things with the same name except for different letter case. As far as Windows is concerned, they actually have the same name. When it comes to assigning drive letters, for historical reasons on most systems, you'll find that the main hard drive is assigned the letter C and then the DVD drive is assigned the letter D, and any drives, in addition to those, are assigned the remaining letters starting from E. For historical reasons, the letters A and B usually go unused. When you name a file in Windows, by convention the file's name should end in what's called a file extension. A file extension is a dot followed by some number of characters, usually just three. And the idea of the file extension is that it denotes the type of the file. So, for example, some common extensions include dot doc, which is the extension used by Microsoft Word documents, dot xcl, which is used by Microsoft Excel spreadsheets, dot jpeg, which is a kind of image format, pdf, which is another kind of document read by this program called Adobe Acrobat, mp3 is a popular audio format, ci is another common video format, dot html is the format for web pages, and dot exe is short for executable, it's an executable program, it's a piece of code that can actually run. These are just a sample of the most common extensions. You'll commonly encounter a couple dozen more. The Windows operating system itself has a bunch of files and these are placed in some standard directories. Assuming Windows has been installed on your main hard drive and your main hard drive has been assigned the drive letter C, then you should find the Windows directory itself at c colon slash windows. This is the directory which contains almost all of the files used by Windows itself. As a user, you generally don't really have any need to go into this directory. None of the files in there really concern you. You should also have on your system a directory called program files. By convention, this is the directory where any files for any other programs installed in your system should be placed. Also on the same drive where Windows is installed, you should have a directory called users. For every user account on your system, you should have a directory in here named after that user account. User accounts are something we'll talk about later, but for example on my system, I log in as Brian and so in my user's directory there is a directory called Brian. And the idea of this directory is that this is a place where I as a user can store any of my own documents, any of my own files, and also it's a place for any sort of configuration files used by any of my programs. It's basically a place for anything that's specifically about me, about my user account. And inside each user directory, just for the sake of organization, Microsoft includes these default directories, one called my documents, one called my pictures, and one called my music. The idea is that any music you have, you would put inside the my music folder any document you create, you would put inside your my documents folder and so forth. Now, nothing at all forces you to put your stuff in these directories, but if you can't think of a better place to put them, you might as well use these directories.