If a Macintosh boots and gives a "Sad Mac" immediately, the problem is
probably caused by either faulty hardware or corrupted boot blocks. If the "Sad Mac" occurs later in the startup sequence, there may be other problems. Use the TroubleShooting Flowchart to diagnose problematic Macin
After the computer finds the Startup disk, it searches for any additional devices attatched to the computer. This is similar to how the Finder "mounts" volumes when it is launched. Without specialized disk drivers or utilities such as SCSI Probe, any devi
ce not recognised at this time cannot be addressed by the computer. This is why all periferal devices should be turned on before the computer itself; so they can be recognised by the initial startup sequence.
Once the computer has found a startup device, it begins to load the
operating system into memory, beginning with the System file. If the Macintosh model is one that requires a system enabler, it opens the enabler soon after it begins loading the System file. If the enabler is n
ot present, a dialog will
appear stating that the operating system is not recent enough to run on
the Macintosh. As the Macintosh is loading the System file (and enabler file), it
will display a "Welcome to Macintosh" dialog box. The text of the startup dialog is stored in the DSAT resource in the system file. Under System 7.5.1, this dialogue box is replaced with a "MacOS" screen with a progress bar. The MacOS image is stored in t
he PICT resource in the "System 7.5 Update" file. The System file contains patches to the Macintosh ROMs, the Macintosh operating system, and system and graphical interface resources shared by the Finder and Macintosh applications.
Once the mac has loaded the system, enabler, and fonts, it begins to
load the Extensions contained in the
Extensions folder within the System Folder. Extensions load
alphabetically. Extensions modify or add to the code already loaded. For
example, when the system draws a button, it uses a specific set of
instructions stored in the system file. An extension may be loaded that
"patches" this code, so that when the mac wants to draw a buton, it uses
a different set of instructions stored inthe resource. Extensions can be
very useful, but because they modify the system code, thaey can cause
problems is they are not written properly. They can also "conflict". If
two extens patch the same code, they may conflict with each other and
cause a crash, freeze, or bomb. This may occur as the extensions are
loading, or after the mac has booted and calls the modified code for the
first time. Extensions can also conflict with the system itself if they
are not written correctly.
After the Extensions load, the Control Panels
are next. The Control Panels usually function exactly like
extensions; they modify or add to the system software. They can also cause
crashes, freezes, or bombs. The only difference is that they typically
have an interface to control their function. Double-clicking a control panel
opens this interface and allows you to customize the control panel.
Control Panels do not always act like extensions, however. Some control
Panels are used to change what is stored in the Monitor control panel, for example, is
used to set the monitor size, position, and color depth, as well as the
location of the menu bar and startup dialog box. The Date and Time control panel is used
to set the system clock. Finally, some control panels modify preference files.
The Views control panel modifies the
"Finder Preferences" file and controls how the finder displays files.
Extensions and Control Panels can often cause problems; because of
this they can be disabled easily during startup. After the "Happy Mac"
appears, holding down the key will prevent the system from
loading the control panels and extensions. The startup dialog will
indicate this by saying "Extensions Disabled".
Once the Control Panels have been loaded, the system loads the Finder. The Finder is an application like any
other Mac application, but it is central to the operating system. The
Finder is the application with which you interact with the operating
system; you use it to find, open, copy, move, and delete files.
It is also the application that you use to open Control Panels and Desk Accessories, restart and shut down
the computer, and unmount storage devices. The first thing the finder
does is mount any storage devices that are connected to the computer and
check their desktop files. If the desktop files are outdated or if the