Extension Conflict
Apple Classic Macintosh
Severity: ModerateWhat Does This Error Mean?
An extension conflict happens when two or more extensions (INITs) in your System Folder fight over the same memory or resources. Symptoms include crashes at startup, random bombs, and freezes. The fix is identifying and removing the conflicting extension.
Affected Models
- All Classic Macs running System 6 or System 7
- Macintosh Plus
- Macintosh SE
- Macintosh Classic
- Macintosh LC series
- Macintosh II series
- Macintosh Quadra series
- Macintosh Performa series
Common Causes
- Two extensions patching the same system trap
- Extension load order conflicts (extensions load alphabetically)
- Too many extensions exhausting the system heap
- Outdated extension not compatible with your System version
- Anti-virus software conflicting with other extensions
How to Fix It
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Hold Shift at startup to boot with all extensions off.
If the Mac starts fine and the problem disappears, it is definitely an extension conflict.
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Use Extensions Manager (System 7.5+) to disable extensions in groups.
Disable half your extensions, restart. If the problem persists, the bad one is in the enabled half. Keep halving until you find it.
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On System 6 or early System 7, remove extensions manually.
Open your System Folder and move extensions out to a temporary folder on the desktop. Restart and test. Add them back one at a time.
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Change the load order using a name prefix.
Extensions load alphabetically. Renaming an extension with a space (or tilde ~) at the start of the name moves it to load first or last. Sometimes changing load order resolves the conflict without removing anything.
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Check for updates for the conflicting extension.
Many conflicts were fixed in later versions of the extensions. Check the developer's disk or online archives (macintoshgarden.org has many classic Mac updates).
Frequently Asked Questions
What is an extension (INIT) on a Classic Mac?
Extensions are small programs that load at startup and add functionality to the system — like modern Windows drivers or browser extensions. They were stored in the Extensions folder (System 7) or the System Folder root (System 6). Because they all loaded into the same memory space with no protection between them, conflicts were extremely common.