On real hardware, the Motorola 68030 executed an undocumented instruction to prevent a system crash at boot, but it caused problems with the emulator.
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(Image credit: Doug Brown ) A computing enthusiast unearthed a 34-year-old Apple Mac bug that should have crippled the system at startup, but it never did, thanks to an undocumented feature in the Motorola CPU that quietly neutralized the flaw. Downtown Doug Brown discovered this Mac Classic II ROM code wrinkle after witnessing a MAME-emulated system crash (in 32-bit mode) that the original hardware would not (h/t PC Gamer ). We tend to agree that “this bug in the ROM would have gone undiscovered for all eternity” if it were not for Brown’s curiosity being piqued.
Brown, who self identifies as “a combined Apple/Linux/Windows geek,” and is a big fan of the open source MAME (the Multiple Arcade Machine Emulator) project. He also tells his readers that this software is “arguably the most complete emulator of 68000-based Mac models,” and that these classic Motorola CPU-based systems are his main use of the emulator. That’s pretty unusual, as MAME is most famous for facilitating classic arcade gaming fun.
The story goes that Brown was indulging in his Mac emulation on MAME hobby when he noticed that an emulated Classic II wouldn’t boot with 32-bit addressing enabled. However, it worked with 24-bit addressing – no ‘sad Mac’ with the 24-bit option toggled on… What was happening? And why was the emulated Mac crashing so badly, so quickly, when the original faced no such issues?
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Key considerations
- Investor positioning can change fast
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Reference reading
- https://www.tomshardware.com/video-games/retro-gaming/SPONSORED_LINK_URL
- https://www.tomshardware.com/video-games/retro-gaming/a-34-year-old-apple-mac-crash-bug-would-have-gone-undiscovered-for-all-eternity-but-the-accuracy-of-the-mame-emulator-shone-a-light-on-it#main
- https://www.tomshardware.com
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