The MacOS has always had the ability to launch
the appropriate application by double-clicking
(or Opening) a document file. This is possible
because the Finder stores file type and creator
codes in the Desktop File, and uses the desktop
file to display icons and launch applications.
All Macintosh files have a "type" and "creator"
code stored within them. The Finder uses these
4-character codes to associate the appropriate
icons to files, and launch the correct application
when files are opened. A "type" code represents
the kind (and format) of the data within the
"TEXT" and "PICT" are two common file types.
Applications can specify proprietary file types
in a BNDL resource that the Finder reads and
stores in the Desktop File; an application like
Microsoft Word has almost 20 different type codes
associated with its data and application files.
Since files with standard type codes (such as "TEXT")
can be opened by several different applications,
every application also has a unique "creator" code
associated with it. When an application creates
a file, it assigns the file the appropriate type
code, and also gives it the application's creator
code. When that file is opened, the Finder looks
up the creator code in the Desktop File and opens
the document in the application associated with
it. With the introduction of System 7.x and Macintosh
Easy Open, the Finder can present a dialogue
box if it cannot find the creator application
on the hard drive. The dialogue box presents
a list of applications that can open the documnet's
file type. The dialogue box also lists applications
that can open the file if it is automatically
translated by Dataviz and/or Claris XTND translators.
What are the Desktop Files?:
The "Desktop File" actually refers to two files;
one a database of "type" and "creator" codes, and
the other storing the various icons associated
with them. If the "desktop file" is corrupted,
files may not be displayed with the correct icon,
or they may be opened in the wrong application.
If the Desktop File contains old or outdated information
(perhaps a newer version of an application has
been installed), similar symptoms may appear. The
Desktop File has been linked to unexplained crashes
and freeses, it is usually a good idea to periodically
rebuild the Desktop File to keep its contents up
to date; but if you are experiencing problems,
rebuilding the desktop doesn't hurt and may solve
The Desktop Files are invisible files stored
in the root level of every Macintosh volume.
Hard drives (or hard drive partitions), CD-ROM
drives, and floppies all contain Desktop files
containing information concerning the files present
on the volume.
Rebuilding the Desktop Files:
As the finder loads, it mounts the volumes attatched
to the Macintosh. When it mounts each volume, it
reads the volume's Desktop File . "Rebuilding" the
desktop file means deleting the old Desktop Files
and creating new ones by scanning the contents
of the volume.
To rebuild the Desktop File
Turn on or restart the Macintosh
Wait until all the Extensions and
Control Panels have loaded
As soon as the startup icons on
the bottom of the screen disapear,
hold down the command and option keys
The Finder should ask you if you
are sure you want to rebuild the
desktop file. Click
If there are multiple volumes,
for each as the Finder asks you if
you want to rebuild the Desktop for
The only side effect from rebuilding the Desktop
File that any information stored in the "Comments"
field of a file is lost. You can see the "Comments"
field by selecting a file and choosing "Get Info..."
from the Finder's "File" menu. Because rebuilding
the desktop file deletes any information stored
here, the comments field has never been utilized
by average users. Unless the comments field contains
important information, it is safe to rebuild
the any time the computer is started up. Do not force-quit
the finder in order to rebuild the desktop;
restart the computer.
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