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System Error 25

Apple Retro Computer

Severity: Moderate

Source: OnlyErrorCodes.com — Every error code. One place.

Mac Classic System Error 25 — Memory Full Bomb

What Does This Error Mean?

System Error 25 on a Classic Mac means 'memory full' — the application asked for memory and the system couldn't provide it.
Often caused by too many extensions, by an app's memory partition being too small, or by genuine RAM exhaustion on a 1MB or 2MB machine.
Restart, increase the app's memory partition in Get Info, or boot with extensions disabled (hold Shift).

Affected Models

  • Macintosh Classic
  • Macintosh Classic II
  • Macintosh SE
  • Macintosh SE/30
  • Macintosh II
  • Macintosh LC
  • Macintosh Plus

Common Causes

  • App's memory allocation in Get Info too small
  • Too many INITs/extensions consuming RAM
  • Truly out of physical RAM on a 1MB-2MB Mac
  • Memory leak in old software

How to Fix It

  1. Force-restart.

    Press the programmer's switch (the small button on the side) or hold Cmd-Ctrl-Power.
    The Mac restarts.
    Don't just dismiss the bomb dialog — Classic Macs can't recover safely from system errors.

  2. Increase the app's memory partition.

    Click the app's icon once.
    File → Get Info (Cmd-I).
    In Memory Requirements, raise both 'Preferred' and 'Minimum' size.
    For a typical app, try doubling the preferred size — say 512K to 1024K.

  3. Disable extensions.

    Restart while holding Shift.
    'Welcome to Macintosh — Extensions Disabled' appears.
    If the app now runs without error 25, an extension was eating RAM.
    Use Extension Manager (or move INITs out of the System Folder one at a time) to find the offender.

  4. Check 'About This Macintosh'.

    Apple menu → About This Macintosh.
    The bar chart shows total RAM, system usage, and per-app usage.
    If the system is using most of it before any app runs, you have too much loaded.
    Clean up the System Folder.

  5. Consider adding RAM.

    Classic Macs have RAM SIMM slots.
    Going from 1MB to 4MB transforms the experience.
    SIMMs for 68k Macs are still cheap on eBay (10-30 USD).

Frequently Asked Questions

Is system error 25 the same as 'not enough memory' message?

Related but different.
'Not enough memory' is the application politely refusing to start.
System error 25 is what happens when the app tried, hit a wall mid-execution, and crashed the whole Mac.
The fix is the same: more memory.