Another change was the move to CMOS gates as the primary method of building complex CPUs. CMOS had been available since the early 1970s; RCA introduced the COSMAC processor using CMOS in 1974. Whereas earlier systems used a single transistor as the basis for each "gate", CMOS used a two-sided design, essentially making it twice as expensive to build. Its advantage was that its logic was not based on the voltage of a transistor compared to the silicon substrate, but the difference in voltages between the two sides, which was detectable at much lower power levels. As processor complexity continued to grow, power dissipation had become a significant concern and chips were prone to overheating; CMOS greatly reduced this problem and quickly took over the market. This was aided by the uptake of CMOS by Japanese firms while US firms remained on nMOS, giving the Japanese industry a major advance during the 1980s.
