IBM has constantly evolved since its inception. Over the past decade, it has steadily shifted its business mix by exiting commoditizing markets such as PCs, hard disk drives and DRAMs and focusing on higher-value, more profitable markets such as business intelligence, data analytics, business continuity, security, cloud computing, virtualization and green solutions, resulting in a higher quality revenue stream and higher profit margins. IBM's operating margin expanded from 16.8% in 2004 to 24.3% in 2013, and net profit margins expanded from 9.0% in 2004 to 16.5% in 2013.