The invalid 68030 instruction that accidentally allowed the Mac Classic II to successfully boot up
SMRTR summary
A rare bug in the Macintosh Classic II ROM should have prevented it from booting in 32-bit addressing mode. However, an undocumented instruction in the Motorola 68030 CPU accidentally fixed the issue by modifying a register value. This quirk went unnoticed for decades until MAME emulation revealed the problem. The discovery highlights how even well-tested hardware can contain hidden bugs and demonstrates the value of emulation in uncovering such issues.
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