The S&P 500 was up 0.4% in midday trading to 2,108.66.
The Dow Jones Industrial Average was up 0.6% to 18,152.11.
The NASDAQ was up 0.5% to 4,962.75.
The yield on a 10-year Treasury bond was up 1.7% to 1.81%.
The price of gold was flat at $1,254.
Irvine-based Western Digital Corp. was up 6% to $43.89 and a $10.2 billion market cap on moderate volume. The memory products maker this week introduced two new products and is receiving favorable financial press coverage following a decline that coincided with its board approving the acquisition of SanDisk Corp.
Irvine-based Impac Mortgage Holdings Inc. was up 12% to $15.90 and a $194 million market cap on above-average volume. The company is a mortgage lender.
Santa Ana-based QuantumSphere Inc. was down 35% to 65 cents and a $15 million market cap on high volume. The chemicals products maker had traded shares by midday at a rate 10 times its 90-day average.