Macintosh: Startup Sequence with Mac OS 9 and Earlier

This document explains the startup sequence your Macintosh computer uses with Mac OS 9 and earlier. Knowing how this sequence works can sometimes help troubleshoot startup symptoms.
With Mac OS 9 and earlier, the Macintosh startup sequence has eight steps:
If your computer will not start up, try isolating the symptom to one of the specific steps.

Step 1: Turn On
When you turn on the computer, the power supply sends voltage to the logic board's electrical circuits, initiating the startup sequence. You should hear the fan and power supply turn on. If absolutely nothing happens, make sure the computer is plugged in. Check the power outlet. Make sure all the cables are securely connected.

Step 2: Hardware Self-Test
After the computer is turned on, different "managers" in the computer's read-only memory begin to function. The first is the Start Manager. It makes sure that certain hardware components on the computer's logic board are working, including the microprocessor, read-only memory, drives, ports, expansion slots, and memory (RAM).

The startup sound you hear when you turn on the computer indicates that the Start Manager has successfully completed its tests. You will also see the raster (gray desktop) on the screen, along with the pointer.

If one of the Start Manager tests fails, you may
The kind of tones you hear will vary depending on the Macintosh model, and on the kind of component(s) that failed the test.

If you hear these tones or see a "sad Macintosh" icon on the screen, contact Apple or an Apple Authorized Service Provider for further troubleshooting.

Step 3: Mac OS Starts Up
In this step, the operating system creates and reserves for itself a portion of the RAM. This area is called the system partition.

Step 4: Search for a Startup Disk
Next, the Start Manager looks for a startup device, usually a disk drive, where the System file is stored. You choose this disk in the Startup Disk control panel. Your selection is saved in the computer's parameter memory (PRAM). If this disk is available, the startup icon appears.

If the disk you chose is not available, the Start Manager searches the system bus(es) for startup devices. (See Note 1). When the Start Manager finds a startup device with a System file, the "happy Macintosh" startup icon appears.

If no startup disk containing a System file is found, you will see either: a flashing "?" icon, or a flashing "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. This symptom could be caused by a software fault--perhaps the System file is not on the startup device, or it could be there but in an unusable state. It could also be caused by a hardware issue--maybe the System file is on the disk but the disk is unusable. Other possible causes include: SCSI configuration, unusable PRAM, and third-party software. For further troubleshooting help with this symptom, see:

Document 58042: "Macintosh: Flashing Question Mark at Startup"


Step 5: System File Is Found and Opens
When a valid System file is located, the System file, and any ROM updates are loaded into the system heap. Other managers are initialized. If this step is successfully completed, then the "happy Macintosh" icon is replaced by the "Welcome to Mac OS" window.

If the computer stops responding, or restarts unexpectedly during this step, suspect a missing or unusable System file. You may need to reinstall the system software.

Step 6: System Extensions Load
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:
If the computer stops responding, or restarts unexpectedly during this step, suspect conflicting or unusable extensions or control panels. See document 30929: "Mac OS: Extension Conflict Troubleshooting/Extensions Manager Features".

Step 7: Finder Opens
The Process Manager loads the Finder into the system heap. When this step completes successfully, the desktop environment with all its icons appears on the screen.

If an alert box appears before the desktop appears, or if it appears while any disks connected to the computer are appearing on the desktop, the computer's hard disk(s) may have an issue. Contact Apple or an Apple Authorized Service Provider for further troubleshooting.

If you see an alert box with the message: "Can't load the Finder!", there may be too many system extensions, not enough RAM, or damaged software. Alerts at this point may also indicate issues with the boot blocks on the startup device. Try reducing the number of extensions, and eliminating an extensions conflict. See document 30929: "Mac OS: Extension Conflict Troubleshooting/Extensions Manager Features".

If this does not work, try reformatting the hard disk and reinstalling the system software. Warning: Reformatting the hard disk will erase all of its contents. Make sure you have backed up all the files you want to keep before reformatting the hard disk.

Step 8: Startup Items Open
The Finder opens any applications or aliases in the Startup Items folder.

Notes
Published Date: Feb 18, 2012