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== ROM Modifications and Development == === ROM SIMM Modules === Many Old World ROM systems use socketed ROM modules: * '''72-pin SIMMs''': Similar to RAM but containing ROM/EPROM chips * '''Capacity options''': 1MB, 2MB, 4MB depending on system * '''Update capability''': Apple could ship ROM updates as replacement modules * '''Third-party modifications''': Enthusiasts created custom ROMs with patches === Development and Debug Features === Apple engineering samples included special capabilities: * '''ROM SIMM sockets with VPP''': Voltage for programming EPROMs in-system * '''Debug ROM versions''': Additional diagnostic output and breakpoints * '''Dual ROM sockets''': Switch between production and development ROMs * '''Serial console output''': Diagnostic messages during boot === Common ROM Patches === The enthusiast community developed various ROM modifications: * '''Memory test bypass''': Significantly faster boot times * '''Checksum disable''': Allow further ROM modifications * '''Boot device patches''': Support for non-standard boot devices * '''Gestalt ID changes''': Enable features on lower-end models
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