Examples:

More info on file extensions: FileInfo.com A searchable database of file extensions and how to open the files

Notice that the last example in the table is what's called a long file name, meaning that it is longer that 8 characters plus 3 for the extension. It also contains spaces. These are both legal under Windows since Win95 and in some other operating systems but not under DOS or Windows 3.x. You would need some kind of additional software to handle such names.
 
Under DOS, file names can have 1 to 8 characters in the FILENAME and 0 to 3 in the EXTENSION. This is sometimes called an 8.3 name.
 
If you are having trouble opening a file with a long file name, try putting double quote marks (" ") around the name, like this: "letter to fred about vacation.lwp"

One way to help is to name the file name with no spaces like: lettertofredaboutvacation.lwp but that is hard to read. Using internal capitals helps like: letterToFredAboutVacation.lwp

Sometimes capitalization in filenames is ignored and sometimes not. Mymemo.txt, MyMemo.txt, mymemo.txt, MYMEMO.TXT are all different names under the UNIX and Linux operating systems but are the same under Win95/98/XP. Don't rely on capitalization to distinguish one file from another. Use a different name altogether and it will be easier on everyone.

Certain characters can't be used in file names. They are reserved by the operating system for special uses.

Illegal characters in a file name: . , / \ : ; [ ] " | =
Spaces can't be used either under DOS and Windows 3.1 and UNIX.

Certain extensions are reserved also. They are used internally by the system.

Illegal extensions: CON, AUC, COM1, COM2, COM3, COM4, LPT1, LPT2, LPT3, PRN, or NUL

More hints on naming files:

If you do a weekly sales report, you could use the month and week number like Sept397.rpt for the third week of September in 1997. Someone new to the office might not understand this though. If you can use long file names, you could be clearer with 3rd Week Sales-Sept 97.rpt.

Think about how your file names will be alphabetized also. You might want to adjust what comes first in the name to get files grouped neatly together that are similar but of different dates. For the September third week sales report, using S9709w3.rpt or Sales9709week3.rpt would automatically put all the Sales reports together alphabetically by year and month and in order by week.

Note that computers normally alphabetize numbers a little differently than you might expect. All the numbers starting with "1" will be put together so "1", "10", and "1000" will all come before "2"!!

Save a File

Now that we've thrashed out how to name a file, it's high time we talked about how to save it.

If you are working in a classroom lab or other shared computer, you'll need to save your files to a removable disk. If you save to the class computer's hard drive, another student or the teacher might erase it before you get to use that computer again. If you have your own logon name and password, then your documents should not be available to others but it will probably not be available to you from a different computer. <sigh!>

Saving to the hard drive is the same as to a removable disk except for inserting and removing the disk.

Steps to Save

1. Insert your removable disk.
(Obvious but often forgotten. A floppy drive will make a scary noise and send an error message that the drive is inaccessible. Another kind of removable disk just won't show up in the list of drives.) A disk must be formatted before it can be used. New removable disks come formatted from the factory.

Sometimes the computer will tell you that the disk has not been formatted and ask "Do you want to format it now?" Be careful! If the disk is blank, go ahead and try to format it. If the disk has data, do not reformat the disk unless you are sure you won't be losing anything important. Computers are sometimes picky about reading disks formatted by a different computer. Note that different operating systems use different formatting schemes. A disk formatted for a Macintosh will not look formatted to a PC, for example, though a Mac can read a PC disk. Don't forget that reformatting will erase all the data.
 
2. Use Save button or File | Save or File | Save As command from the program's menu.

3. Name the file  If the file is new or you chose Save As, you'll get a dialog box where you enter the file's name

4. Choose a directory/folder (more on directories/folders in the next section.)

For removable USB disks: Your flash drive may not show in the Save in: drop list at first. It's not broken! Choose My Computer from the drop list and all drives will show in the white area below, including your flash drive. After you have accessed the USB disk by opening a file or saving a file to it, then the USB drive will show in the drop list.

5. Choose a file type  For example, in Win95's WordPad, as pictured here, you can save a file as a Word 6.0 document (extension = doc), in Rich Text Format (extension = rtf), as a plain text document (extension = txt), or as a MS-DOS text document (extension = txt). A graphics program like PaintShopPro might offer 30 or more different file formats.

6. Remove the disk. But wait for the drive light to go out first! The computer is not through writing until the light goes out.

For removable USB disks: The light may stay on after writing is done. Look in the notification tray at the bottom right of your task bar for an icon called Remove Hardware Safely .

Click the icon and a list pops up of the USB devices that are currently connected.
   (These may not all be drives!)
Click on the drive you want to remove.
Wait for the light to go off and a message to appear that says it is OK to remove the hardware now!
Remove the device.

For removable USB disks: If you remove a flash drive incorrectly, the computer may no longer recognize any device in the port it was using. You will have to reboot the computer to fix this.

When you modify a file and save it, you are overwriting the previous version. If you want to keep the old version, too, save the file with a new name or in a different folder. However, having different documents around with the same name, even if they are in different folders, can be quite confusing.
 
If you try to save a file to a folder that already has a file with that name, most programs will ask if that is what you really want to do. Read the message carefully to be sure that you are overwriting the correct file. Test your software to make sure that you will get a warning! Some programs allow you turn off this feature and a few just assume you know what you are doing!

Once you've decided on a file name you must deal with the question of where to put it! So the next topic is Directories / Folders.