[rasz]

And it wouldnt even be that hard, just two 2kx8 SRAMs (like the ones in every NES/Famicon) and CS line going from the chipset to map it somewhere high outside the range of the chipset was very logical, easily doable in 1987 and most importantly cheap. Those 6116 srams were below $2 retail in 1987 (Byte magazine retail prices), so $4 for big performance boost.

Hell, smart Commodore would design A500 with second trapdoor near the CPU. Ship unpopulated but offer official Commodore "turbo ram" expansion carts:

- $25 4KB version. $8 BOM, 2x $1.95 6116

- $40 8KB. $12 BOM, 2x $3.5 6264

- $100 64KB. $28 BOM, 2x $12 62256

- Extreme $400 256KB. $120 BOM, 8x $12 62256. Would stick out due to big PCB so make it an attractive piece of plastic with cool logo and "EXTREME" design.

Map it at D80000 (potential 256KB of space for activities) and let software vendors auto detect fitted option by running quick memory test. Easy speed boost and easy extra money for Commodore.

[lproven]

I tried to answer at greater length here:

https://news.ycombinator.com/item?id=45745754

But I think in reality, less money for Commodore because of sales lost to the now-even-cheaper Atari ST.