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The Computer Guy's TroubleShooting Pages

The Startup Process
How your Macintosh starts up. How that process can go wrong - the "Sad Mac", the "Flashing ?", stalls, freezes and error messages.


Updated 8/28/99

 Understanding a process and it's design can improve your chances of diagnosing and solving a problem. (not only with computers, but autos and plumbing, also)

Power On - to - Welcome to Macintosh
Startup Diagnostic
As soon as the Mac is turned on, it runs a diagnostic test stored in ROM (Read Only Memory). Part of the Macintosh Operating System is in ROM as well. This part of the Operating System is now software in iMacs and G3s.
The startup hardware diagnostic checks the memory, boot blocks, and other componants. For example, the diagnostic checks a specific location in the boot sector that is written when the system is properly shut down. If the computer was not shut down correctly the last time it was on, the diagnostic will see this, display the "Improper Shutdown Dialog Box" and perform a quick test of the file structure of the hard drive. The improper shutdown warning can be disabled in the General Control Panel. If the diagnostic tests fail, the Macintosh will halt startup and display the "Sad Mac" or a Flashing ? DIsk Icon or System Folder icon.
If you see any of these icons, there is a hardware or software problem. The most common causes are:
&emdash; Corrupted Boot Blocks
&emdash; Corrupted System File
&emdash; Corrupted System Enabler
&emdash; Corrupted Font
&emdash; Corrupted Finder File
&emdash; SCSI Chain Errors
&emdash; Faulty, conflicting, or incorrectly installed memory chips
&emdash; Faulty, conflicting, or incorrectly installed expansion cards
&emdash; Physically damaged hard drive or hard drive interface
&emdash; Corrupted or conflicting storage device driver(s).
&emdash; Physically damaged motherboard
&emdash; Physically damaged power supply
&emdash; Inadequate electrical power
If a Macintosh boots and gives a "Sad Mac" immediately, the problem is probably caused by either faulty RAM, hardware or corrupted boot blocks. If the "Sad Mac" occurs later in the startup sequence, there are other problems.
Power Key pressed or Power button/switch pressed
Failure: grey desktop does not appear, no startup chime
Cause: PRAM battery dead, power cord loose, dead power supply, keyboard not plugged in, keyboard defective
1. Gray desktop pattern appears on screen.
A. The motherboard is tested
Symptom: Sad Mac Icon
&emdash;Cause: damaged motherboard or powersupply, improperly seated card or ROM, conflicting ROMs
&emdash;Repair: Reseat memory SIMMs, reseat Nubus or PCI cards, find Authorized Service Center.
B. The RAM is checked.
Symptom: Sad Mac Icon
&emdash;Cause: damaged RAM SIMM/DIMM, improperly seated RAM Module, improper RAM SIMM order
&emdash;Repair: Reseat all SIMMs, verify configuration with GURU (Newer Technology) or Apple Spec Database, remove SIMMs one at a time (on in pairs) and test.
C. The ROMs on Nubus or PCI cards is read and becomes part of the system.
Symptom: Sad Mac Icon or white box at top of grey screen or splash screen of added video card
&emdash;Cause: improperly seated card, conflicting ROMs (normally happens at majorSystem Upgrade or computer upgrade)
&emdash;Repair: Remove cards and restart - manufacturer may have ROM upgrade available (chips or software)
2.. The SCSI bus is reset or initialized.
Why: This is to make sure the bus was not left in a bad state at shutdown or due to a crash.
Symptom: Sad Mac Icon
&emdash;Cause: improper termination, excessive cable length, duplicate SCSI ID numbers, defective SCSI device or cable.
&emdash;Repair: Correct the problem. (See SCSI Problems)
3. The SCSI port is checked.
The Mac checks SCSI IDs (from 6 to 0) to find attached drives and devices on the inbuilt SCSI chain. A table is created tracking all connected disks and devices. This is repeated for systems containing two or more SCSI chains. For Ultra and Ultra2 SCSI ports the device can have 15 ID's (from 14 to 0).
For connected drives, the ROM boot code will use the SCSI Manager to check SCSI partition information to locate the driver . Partition information is checked to ensure that the device is valid.
These steps are repeated for each drive connected. At this point, there may be a number of drivers in memory, but there are no volumes, since none have been mounted yet. There can be one driver for each drive, some drivers will handle multiple drives.
Loading the PRAM
Startup Disk
After the diagnostic test, the computer looks for a startup disk. Any disk can be a startup disk (hard disk, floppy disk, CD-ROM, etc) as long as it contains a "blessed" system folder. If there is a diskette in the floppy drive, the computer will check it first for a blessed system folder. If it doesn't find one, the Macintosh will eject the floppy and scan the SCSI chain for a blessed system folder, starting with the internal hard drive (SCSI ID #0).
A startup disk's System folder must contain both a System File and a Finder File. Some models running a specific OS version also require a system enabler. Once the computer finds a blessed System folder, it will begin loading the operating system (ignoring any other System files on the disk). On startup, the mac loads the operating system files contained in the System Folder; ignoring any other system files on the hard drive.
When the computer searches for a bootable system disk; it checks each disk's boot blocks for a "blessed" system folder. When a System folder is "blessed" (System Folder will have a small icon on it, if not blessed it will be a plain folder), the folder's identification number (all Macintosh folders are given a unique number when they are cr eated) is written into the boot blocks. As the Macintosh checks for a System folder, it finds the ID number in the boot blocks and then checks the specified folder for a System File and a Finder. The process of writing the System folder's ID number into the boot blocks is known as "Blessing" the System folder. If the computer does not find a blessed System folder, it will display the "flashing disk" icon:
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.
4. Determine the startup disk.
The startup device will be
1) Floppy (except on iMacs or newer models that do not include a builtin floppy)
2) Designated Drive (Startup Disk Control Panel)
3) Internal SCSI Chain ID 6, 5, 4, 3, 2, 1, 0
4) External SCSI Chain ID 6, 5, 4, 3, 2, 1, 0 4 (if it exists)
5) Additional SCSI Chain ID 6, 5, 4, 3, 2, 1, 0 4 (if it exists) 14, 13, ... , 0 (if an UltraSCSI chain)**
** Except of certain proprietary cards (ie, Avid) that limit the number of recognized drives
This device selection is modified by keyboard commands:
Eject Floppy and removables at Startup [Mouse Button]
Bypass internal or normal startup drive [CMD]+[OPTION]+[SHIFT]+[DELETE]
Boot from CD (Late model Apples) [C]
Mac OS8 - Starting a 68040 computers from a CD-ROM using the c key may not work when the CD's SCSI ID is 5.
Boot from a specific SCSI Drive [CMD]+[OPTION]+[SHIFT]+[DELETE]+[#] (# = SCSI ID#)
Some Hard Drives require a longer time to become available than the computer does and need to be turned on first.
If there is a floppy available it will always be the startup disk. During this process the disk chosen as the startup disk is not known to be valid. The System file and boot blocks are checked later.

There isn't a search for floppy devices, the floppy driver is contained in the ROM and will notify the System when it detects one.The first floppy found will be used as the startup disk. If there are multiple floppy drives, the others will be mounted by the Finder. During the startup sequence there is only one volume mounted (at execution of the Macintosh boot blocks). The others are mounted by the Finder.

The Startup Disk Control Panel allows the user to choose which device the system should try to boot from first. The drive number, driver reference number, and driver OS type are stored in PRAM to allow a chosen device to be the boot disk. Remember, however, that the floppy drives still have precedence over SCSI devices. If the drive number that is stored as the Startup Disk is invalid, or has a read/write error, the next disk in that chain (or the next chain, if availble) will be chosen as the next bootable candidate.
Symptom: Flashing ? Disk Icon until viable boot drive is found
&emdash;Cause: Damaged Startup Disk's Boot Blocks or System File or missing System FIle or enabler.
&emdash;Repair: Boot from Emergancy Device and replace the damaged System File or enabler OR reinstall System Software.
5. Execute the Macintosh boot blocks.
Once the Startup Disk has been determined, the boot blocks are read from blocks 0 and 1 of the volume. The boot blocks define various parameters in the system, such as whether a debugger will be loaded, the name of the startup program (not always the Finder), the size of the event queue, the size of the system heap, and others.
After the boot blocks are read and verified, the happy Mac icon is displayed . The happy Mac basically means that valid Macintosh boot blocks were found.

Device Problems at Happy Mac

Symptom: Flashing Happy Mac Icon replace by Flashing ? Disk Icon
&emdash;Cause: Damaged Startup Disk's System File or System Enabler
&emdash;Repair: Boot from Emergancy Device and replace the damaged System File or enabler OR reinstall System Software.

Symptom: Happy Mac appears briefly and disappears, and then a floppy-disk icon (or system folder icon on G3's and iMacs - which do not have a floppy drive) appears with a blinking question mark.

&emdash;Cause: Bad boot blocks, corrupted diskdata structure, or corrupted system files.
&emdash;Repair: Boot from Emergancy Device and replace the damaged System File or enabler OR reinstall System Software.

Symptom: Happy Mac flashes on and off; drive does not boot.

&emdash;Cause: Bad boot blocks or corrupted System File or Enabler.
&emdash;Repair: Run recovery program; reinstall Apple System software.

Symptom: Happy Mac appears, but the drive seeks repeatedly before bootinq.

&emdash;Cause: Improper shutdown from a bomb, crash, freeze or power outage &emdash; all file structures were not properly updated before the crash. On the next power-up, the Mac finds that the structureshave been left in an unknown state and verifies them. This is the reason for the long delay while the happy Mac is displayed. This may cause no further problems.
&emdash;Repair: Run Apple's Disk First Aid v8.2 or newer to verify thedisk.
Symptom: Flashing Happy Mac Icon replace by Flashing ? Disk Icon
&emdash;Cause: Newly installed CPU upgrade or accelerator, PRAM is not consistant with new configuration.
&emdash;Repair: Zap PRAM with keyboard command or TechTool (or similar utility) OR press the CUDA button on motherboard. (See directions for upgrade or accelerator)
6. Mount the Startup Device volume.
If the mount fails, the process starts over at the point where a startup, disk is being chosen (step 4 above) . The failing volume is removed from the list of candidates.
Symptom: Flashing Happy Mac Icon replace by Flashing ? Disk Icon
&emdash;Cause: Failure of designated Startup Disk's Boot Blocks or System File
&emdash;Repair: Run Norton Disk Doctor, TechTool Pro, MacMedic, or Disk First Aid v8.2 or newer to verify thedisk.

7. The System file is found and Working Directory is created.

The directory ID is set to the blessed folder. The blessed folder is saved in the volume header as part of the FinderInfo field. If the directory ID is wrong, the System file won't be found, causing it to start over again (at step 4).
Symptom: Flashing Happy Mac Icon replace by Flashing ? Disk Icon
&emdash;Cause: Failure of designated System File or Hard Drive Directory Damage
&emdash;Repair: Run Norton Disk Doctor, TechTool Pro, MacMedic, DiskWarrior or Disk First Aid v8.2 to verify thedisk.
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 not present, a dialog will appear stating that the operating system is not recent enough to run on the Macintosh.
Symptom: Dialog box - This system is not current and can not run on this Macintosh Model.
&emdash;Cause: Missing or damaged System Enabler
&emdash;Repair: Replace System Enabler, OR reinstall System Software
The System file is opened. If the file can not be opened, the process starts over again (at step 4). The Startup Screen is then loaded and displayed. If there is no Startup Screen, the normal "Welcome to Macintosh" message is displayed. Seeing a Startup Screen or "Welcome..." means that the System file was found and opened successfully. This is true for all but the Mac Plus, SE, and other 64K ROM machines, where the Startup Screen is displayed before the System file is opened.
David Anders The Computer Guy 206-286-8438
Copyright © 1998 David Anders The Computer Guy
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