On the Macintosh: Icons
Both Windows and the Macintosh make heavy use of icons to represent disks, files, and folders on the computer. Using the View menu, you can specify how you’d like the icons in a particular window to appear.
In Windows, document icons are associated with filename extensions—a file with the extension .doc, for example, gets the Microsoft Word icon. On the Macintosh, however, the filename has nothing to do with the icon. Instead, every file on the Macintosh stores two invisible, four-letter codes—one that associates it with a particular application, and the other with the particular document type. (Without add-on shareware, there’s no way to edit these codes.)
Custom icons. You can change any Macintosh icon except those used by special folders and the Trash. To give a file or folder a custom icon, follow these sample steps for giving your hard disk a new icon.
This example assumes that you’ve already created and copied a replacement icon, ready for pasting onto another Macintosh file icon. If you’re handy with the graphics program, use it to create a picture no larger than 32 pixels square. Icons with a solid black or very dark border work best and prevent “Desktop color bleed-in” at the end of the process.
Select your hard disk’s icon on the Desktop. Choose File → Get Info (Command-I) to open its Get Info window.
Click the hard disk’s icon in the upper-left corner of the Get Info window. Choose Edit → Paste to paste the new icon over the default ...