The slowing sales growth has been attributed to the maturing PC market, which constituted 66% of Dell's sales, and analysts suggested that Dell needed to make inroads into non-PC businesses segments such as storage, services and servers. Dell's price advantage was tied to its ultra-lean manufacturing for desktop PCs, but this became less important as savings became harder to find inside the company's supply chain, and as competitors such as Hewlett-Packard and Acer made their PC manufacturing operations more efficient to match Dell, weakening Dell's traditional price differentiation. Throughout the entire PC industry, declines in prices along with commensurate increases in performance meant that Dell had fewer opportunities to upsell to their customers (a lucrative strategy of encouraging buyers to upgrade the processor or memory). As a result, the company was selling a greater proportion of inexpensive PCs than before, which eroded profit margins. The laptop segment had become the fastest-growing of the PC market, but Dell produced low-cost notebooks in China like other PC manufacturers which eliminated Dell's manufacturing cost advantages, plus Dell's reliance on Internet sales meant that it missed out on growing notebook sales in big box stores. CNET has suggested that Dell was getting trapped in the increasing commoditization of high volume low margin computers, which prevented it from offering more exciting devices that consumers demanded.