Here is a Feb. 1994 MacWeek Article on OptiMem & RAM Doubler. Note the last paragraph. Although I've not run RAM Doubler on my current SE/30, I did use it in years past on 68000 Macs and PPC Macs. While the slow-down varied, I never found it to be as fast as real RAM (surprise, surprise). And watch out for extension conflicts because they do exist. But as MacWeek properly states, if you are desperate and need a minor RAM boost but can't add RAM, then these product do help.