By Rex Crum, MarketWatch SAN FRANCISCO (MarketWatch) -- Tech stocks edged upward Thursday, with Nvidia Corp. and ARM Holdings among the top advancers after the announcement of a new partnership between the chip makers. Nvidia (NVDA) shares rallied more than 8% after the graphics-chip maker said late Wednesday that it will begin developing central processors for PCs based on a design from ARM Holdings PLC (ARMHY). ARM's shares rose more than 5%. The move is seen as a challenge to Intel Corp. (INTC), which has been making inroads into Nvidia's graphics-chip business. Gains also came from Marvell Technology Group Ltd. (MRVL), JDS Uniphase Inc. (JDSUD), Ciena Corp. (CIEND) and NetApp Inc. (NTAP). Microsoft Corp. (MSFT) edged up 3 cents to $28.02. Chief Executive Steve Ballmer said in a keynote speech at the Consumer Electronics Show that Microsoft has sold 8 million of its Xbox Kinect videogame units since November, and he laid out plans to expand the reach of the Windows operating system platform. The Nasdaq Composite Index (RIXF) rose 7.7 points to 2,709, while the Philadelphia Semiconductor Index (SOX) advanced more than 1%. Declines came from MetroPCS Communications Inc. (PCS), which tumbled 7%. The discount wireless-service carrier said its net-subscriber additions fell 6% in the fourth quarter. Shares of Sourcefire Inc. (FIRE) slid 7.5% after the network-security-technology company said it would acquire Immunet for $21 million.