Amiga 500: Using your trapdoor expansion as chip mem
Back when the Amiga 500 was popular, most people equipped it with extra memory for a total of 1MB, because a lot of games required it. I always thought this memory, which you install in the trapdoor slot underneath the Amiga, was "Chip mem". Turns out it's not.
If you use the excellent WHDLoad to play games on a Amiga 500 you will become aware of this too. Because WHDLoad does all kinds of patching to get the games running, it requires more memory than if you had just ran the game from floppies.
I recently got hold of a A500 and installed extra memory. I noticed WHDLoad often complained that I didn't have 1MB chip memory, even though I have 8MB fast mem. And indeed, both Workbench and Sysinfo reported 0,5MB chip, but the trapdoor memory was reported as slow mem.
Luckily you can pretty easily change some jumpers on the A500 motherboard to make the Amiga address the expansion as chip memory. This only works on revision 6A, which I believe is the most common model.
Read this guide first - it's good, but I thought I would post some pictures to make it even easier for other people. You will need a exacto knife, scalpel, or razor blade to cut the traces. And a soldering iron to connect two solder pads.
JP2 jumper: Cut the trace between pad 2&3. Connect pad 1&2 with soldering iron.
JP7A: Cut the trace between pad 2&3.
Voilá! Your A500 will now address the extra memory as chip mem.