TOPIC
This article provides the Macintosh startup sequence to help in troubleshooting your Mac OS-based computer.
DISCUSSION The Macintosh startup sequence has eight steps. 1. Power up. 2. Hardware self-testing. 3. Macintosh Operating System starts up. 4. Search for a startup disk. 5. System file is found and opened. 6. Extensions are loaded. 7. Finder is launched. 8. Startup Items folder is searched. If there is an issue on starting up, try isolating the condition to a specific step. The following descriptions of the startup sequence steps will help you do that. Power Up During the power up step, the power supply sends voltage to the logic board electrical circuits, initiating the startup sequence. You should hear the fan and power supply come on. If absolutely nothing happens, suspect a power issue and check the power outlet, cables, and all connections. Hardware Self-Testing Hardware is initialized by invoking different "managers" that live in ROM. The first manager to be invoked is the Start Manager, which resides in the Macintosh Operating System ROM. The Start Manager verifies that all hardware components on the logic board are working. Start Manager continues the startup sequence by initiating tests of CPU, ROM, drives, ports, expansion slots (NuBus and PCI), and finally RAM. The startup chord, or boot tone, indicates this step is successful; this sound is in ROM. Also, the raster (gray desktop) appears on the screen, along with the pointer. If something happens to interrupt the startup sequence at this point, you hear a series of tones (called "error tones" or "death chimes"). Different Macintosh computers sound different tones to identify various problems. The tones are stored in ROM. A "sad Mac" startup icon may also display. Because different ROM chips are used in different Macintosh computers, Macintosh models may behave differently during the hardware self-test. Macintosh Operating System Starts Up In this step, the operating system creates and reserves for itself a portion of the RAM that has just been tested. This area is called the system partition. Search for a Startup Disk Next, the Start Manager directs the search for a startup device that contains the System file, looking at the first internal floppy drive, then the second internal floppy drive, and finally an external floppy drive. Note : In dual floppy drive systems, the first drive is the right or lower one. After searching the floppy drives, the Start Manager looks inside the Startup Disk control panel (if you have indicated one) which is saved in battery powered PRAM. The Start Manager continues its search along the SCSI bus looking for startup devices in order of descending SCSI ID number. When the Start Manager finds a startup device with a System file you see the startup icon. If a startup device containing a System file is not found, you see one of two indicators: a blinking "?" icon, or a blinking "X" icon. Either icon means that something is preventing the System file from ending up where it is supposed to be--in the sub-area of the system partition called the system heap. The indicator could be caused by a software problem--perhaps the System file is not on the startup device, or it could be there but in an unusable state. The indicator could also be caused by a hardware situation--maybe the System file is on the disk but the disk is unusable. (The boot blocks on the disk point the way to the "blessed" System Folder where the System file lives.) Other possible sources of an issue at this step include: SCSI configuration, unusable PRAM, and third-party software. System File Is Found and Opened When a valid System file is located, the System file, containing ROM patches (updated routines overwriting their older counterparts), is loaded into the system heap. Other managers are initialized. If the step completes successfully, then the happy Mac is replaced by the "Welcome to Macintosh" dialog box. If the system stops responding, or a spontaneous restart occurs during this step, suspect a missing or unusable System file. Extensions Are Loaded Other resources are loaded into the system heap as the Start Manager searches through the System Folder's Extensions folder and Control Panels folder. Finally, any extensions found at the root level of the System Folder (the level displayed in the System Folder window when you open the System Folder) are loaded. If all goes well, icons representing extensions and control panels appear along the bottom of the screen as they are loaded. Pay close attention to this display as it may help you in troubleshooting. The icons should appear in this order: 1. extensions in the Extensions folder, in alphabetical order 2. control panels in the Control Panels folder, in alphabetical order 3. extensions loose in the System folder, in alphabetical order If the system stops responding, or a spontaneous restart occur during this step, suspect conflicting or unusable extensions or control panels. Finder Is Launched The Finder is loaded into the system heap by the Process Manager. When this step completes successfully, the desktop environment with all its icons appears on the screen. An error message that appears before the desktop appears, or that appears while any physically connected disks are mounting, may signal a hard disk issue. A "Can't load the Finder!" alert box may signal too many extensions and not enough physical RAM, or software defects. Errors at this point may also indicate trouble with the boot blocks on the startup device. Startup Items Folder Is Searched The Finder launches any applications or aliases in the Startup Items folder. Troubleshooting the Startup Sequence Troubleshoot the startup sequence by first understanding the components and outward signs of a healthy startup. When there is an issue in the startup sequence, focus on the likely area(s) where the startup sequence is interrupted. |
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