Both companies gained because smaller manufacturers Via Technologies and Transmeta, which together account for less than 2 percent of the market, shrunk. Transmeta recently stated that it needed to find a partner to continue to stay in the chipmaking business.More info at Cnet
Intel and AMD both gained marketshare in Q4 2004

Intel and AMD both gained market share in the processor market during Q4 2004. Intel rose 0.2 percent up to 82.2 percent and AMD hold 16.6 percent, an increase of 0.6 percent.