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Old 16 October 2019, 14:48   #13
Daedalus
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Join Date: Jun 2009
Location: Dublin, then Glasgow
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The "issue" is that the slot was primarily designed for SRAM memory cards that were mapped straight into the Amiga's address space, either as fast RAM or as storage. Unfortunately this space coincides with the upper 4MB of Zorro-II space, meaning only one can be used at a time. With versions of Kickstart up to 3.0, no checks were done, and so inserting an SRAM card with 8MB of fast RAM fitted resulted in a conflict and instant crashes, refusal to boot etc.

This wasn't an issue prior to Kickstart 3.0, since 8MB of fast RAM wasn't doable in an A600 at the time. But it turned out to be an issue in the A1200, with its expansion slot designed for easily adding 8MB RAM cards. To prevent the clash, a check for this issue was added to Kickstart 3.1, which disables the PCMCIA port when 8MB of Zorro-II RAM is detected.

This solved the clash, meaning no crashes or failure to boot when a card was inserted. It wasn't until later on that I/O-only cards like CF card readers and network cards became a thing, and people realised that the 3.1 fix also prevented the use of cards that didn't need the Zorro-II space.
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