![]() As the Mac-II ROM is 256KB in total, the ROMs should be 64KB each, indicating the EPROMs should be 27512s. ![]() The first link in the comments together with the images of the motherboard indicate the original ROM chips are not EEPROMs but UV Erasable EPROMs of the 27XXX type. I'm not familiar with the way that Mac ROMs are distributed, but if you have a single ROM image file you should split it into 4 parts, with every first 8-bit byte going to the "low" ROM, every second byte going to the "medium low" ROM, every third byte going to the "medium high" ROM and every fourth byte going to the "high" ROM. In the Repair and Upgrade guide (page 197), the ROMs are refered to asĪs the Mac-II is a 32-bit "big-endian" machine this would mean U3 contains bits 0-7 of every 32-bit word, U4 contains bits 8-15, U5 contains bits 16-23 and U6 contains bits 24-31. I'm not very familiar with Macintosh, so my answer is based on my general knowledge of the Motorola 68K architecture (like the 68020 that the Mac-II is based on).
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