A Page about Files and File Systems

A "file" is the most basic unit of organization of computer software. Anything a computer uses or operates on is contained in some sort of a file.

Two broad types of files are program files, also called "executable" files, and data files, also called....files.

The computer's means of organizing files is called the "file system." Every computer has a file system of one sort or another, and a tool for viewing and managing the file system. In Windows, most people are familiar with "My Computer," which is actually only half of the Windows file system tool. More about that later.

Folders and Directories

Before the advent of Graphical User Interfaces or "GUIs" (pronounced "gooies") the various divisions of the file system were referred to as "directories."

When GUIs arrived, with the Macintosh, the "folder" metaphor caught on pretty quickly, so that hardly anyone knows what a directory is today. That's a shame, because "subdirectory" sounds so much better than "subfolder," which also goes a long way toward explaining why you never hear anyone use the term "subfolder."

Here's a graphic of a few folders:

These folders reside on the first hard drive in the system, called the C:\ drive. The topmost folder, the one called "A Folder," has several other folders "nested" inside it.

The plus sign (+) beside one of the folders mean that there are additional folders "nested" inside that one as well. Clicking just the plus sign will "expand" the folder, revealing the nested folders inside. Likewise, clicking the minus sign (-) will "collapse" the view so that only the topmost folders are seen.

Paths

Suppose there were a file named "some_picture.gif" on this computer, and suppose further that we wanted to tell someone, or for that matter, the computer itself, exactly where that file was located within the file system.

To do that we use a "path."

In the picture above, if the file "some_picture.gif" were in the folder called "Enough with the Folders already," then the path to that file would be:

C:\A Folder\Another Folder\Enough with the Folders already\some_picture_file.gif

As you can see, each folder is separated from the one below it by a "backslash," and the very last thing in the path is the name of the file itself.

Paths don't have to be that complicated. For example, if the same file were not in any folder at all, the path would be:

C:\some_picture_file.gif

In this case, we say the file is in the "root" of the C:\ drive. That's because the file system with all of its directories and subdirectories is supposed to resemble an upside down tree and each directory is a "leaf" on the tree. That's quite a stretch for most people I think.

Filenames and Extensions

Let's talk about that filename for a minute: "some_picture.gif." In Microsoft Windows we could type that filename any old way, so "some_picture_file.gif" and "some_PICTURE_file.GIF" and even "soMe_piCture_fiLe.gIf," would all open the very same file. This is because Windows filenames are not "case sensitive." Any variation of uppercase and lowercase letters still refers to the same file. In many other file systems, however, this is not true, so that "some_picture.gif" and "SOME_PICTURE.GIF" would refer to two different files.

In Windows you can also give files names that are as long as you want. That wasn't always so. Filenames under early versions of Windows, and Windows predecessor, DOS (an acronym for "Disk Operating System") could only be eight characters long, with a three character "extension."

The extension, of course, is that part on the right of the "dot" that tells you, and the computer, exactly what kind of file you are dealing with. So, for example, a Word document has the extension ".doc" and of course you are familiar with the most used graphics file types ".gif" and ".jpg." HTML files have the extension ".html" on most systems, but you'll often see them called just ".htm." That's left over from the old Windows restriction: ".html" just wouldn't work on the old Windows.

Programs, or the "executable" files I mentioned earlier, have the extension ".exe." If you look in your Program Files folder, you'll see, in each program's own folder, that there is at least one, and sometimes several, .exe files, as well as several "supporting files" of various types. In general, if there are several .exe files the one with the name most similar to the name of the program is the main one.

Microsoft has decided that people really don't need to know about filename extensions, so that Windows Explorer and My Computer on most people's computers won't display them. You have to explicitly turn on the setting that lets you see them in Windows Explorer before they will appear.

Explorer: the Windows File System Management Tool

Here's a graphic of Windows Explorer. Note that this is not to be confused with Internet Explorer, which is a different application.

Here we have a directory called "Python24" open. It's highlighted in the left side of the window. We can see where the Python24 directory is in relation to the rest of the file system in the left side, and we can see the contents of the directory in the right side.

The right side also shows a lot of information about the files, including the filenames, the size and type of each file, and the date it was last modified. You can customize this view so that it shows you all kinds of other information about the files if you need to. You can also sort the files by clicking on the header of each column, so that I could, for example, sort by type, by size, or by date modified, as well as by filename.

"My Computer," as I mentioned earlier, is only half of Explorer: it only shows you the right side.

Explorer makes the task of moving files around within the file system relatively easy. You can click on anything in the right side of the window to highlight it and drag and drop it anywhere in the left side. That is, to a different folder. It's a lot harder to do that with My Computer. To start off with you have to have two windows open. How you're supposed to find the folder you want that way has never been entirely clear to me, but then, I haven't bothered thinking about it much. I just use Explorer.

Note again the plus and minus signs beside folders with other folders nested inside them. They are a handy feature because clicking just the plus or minus sign lets you see what folders are inside other folders without losing your place: you don't change the view in the right side of the window unless you click on the folder itself.

That's All for Now

I think that's probably enough for you to think about for now, but just a couple of historical notes before I stop: that eight character file name with the three character extension was called the "8.3" format.

Also, the reason that the "C:\" drive is called that is that before very many personal computers had hard disks, back when they had only floppies, the first floppy was called the A:\ drive, and if you were lucky enough to have two floppies, the second was called the B:\ drive.

Having two was a great convenience, because you frequently had to copy floppies and if you only had one it was a great time consuming struggle involving taking out the first disk, inserting the second, taking that one out, reinserting the first...many, many times. In those days, floppy drives were a great deal more expensive than a very large hard drive is today, so most people had only one. It's called "economies of scale," I believe.

To be continued...

Some useful links:

Wikipedia article on "File Systems"

Search for that Unfamiliar File Extension