Saving, Retrieving, and Resaving Files
As you learned in Chapter 2, "Anatomy of a Computer," after something is stored, whether on your hard drive or on a floppy disk, you can always copy it back into memory when you want to use it again (just as you can fetch a particular document from your file cabinet). This is known as retrieving data or opening a file.
Just like when you load a program from your hard disk into memory, when you retrieve data from your hard disk or a floppy, the original copy of that data remains in place and intact on the disk. If you then change the copy in memory, you end up with two different versions: an older version on disk and a newer version in memory. The same situation occurs when you save a new document but continue working on it. You might, for example, get halfway through writing a letter, save your data to disk, and then continue with the letter. You then have two separate and independent versions of the same letter: one (the older one) on disk and another (the current one) in memory.
Saving Your New Version
This has a couple of implications. First, if you like the new version better than the old one, you must remember to save it before you leave the application program. Otherwise, you'll have only the old version of the document (the one on disk) and your changes will be lost. (Most programs politely inquire whether you want to save if you try to close a file that you've modified since the last save.)
Closing Without Saving
Second, if you decide that you prefer the older version, you can close the document (remove it from memory) without saving it. When you do so, the version of the document currently in memory is erased. You can then retrieve the old version (the one on disk) and start amending it again. This can be extremely convenient when you completely bungle an edit and want to start all over.
Replacing the Old File with the New One
Whenever you want to save a file that has already been saved once, you need to decide whether to use the same filename as last time or a new filename. As mentioned, if you copy a file to a disk and the disk already contains a file of that name, the new one replaces the old one. The same issue arises when you resave a file. Suppose you create a budget in your spreadsheet program. Halfway through the process, you save your data; then you revise it and save it again. If you resave it under the original name, the new version will replace the old one. Most of the time, this is exactly what you want.
Keeping the Old and the New Versions
In some cases, however, you'll want to keep both the old and the new versions of the file. If so, you need to resave the file with a new name or in a new location. If you regularly save multiple versions of files, developing some sort of system up front can ward off many migraines later down the line. You might want to save all the old versions in a separate directory, or save all the new versions with the word "new" or a number indicating which draft this is.
The Save and Save As Commands
In Windows, there are separate commands for resaving a document under its existing name (thus overwriting the previous version) and for saving a copy of the file under a new name. You use the Save As option on the File menu rather than the Save command when you want to save something under a new name.
Protection Against Overwriting Files
If you try to save a file with a name that's already in use, many application programs ask for confirmation to ensure that you don't accidentally overwrite the existing file.