Apple’s stock fell as much as 5% after the company said it would give customers a $500 discount to their purchase of a new Mac or Windows laptop.
The company’s stock dropped as much at $27.89 a share on the Nasdaq.
Macs and Macs running Mac OS X 10.9.4 were up 0.5% in early trading.
Macs and Windows 7 PCs were up about 2%.
The Nasdaq index of stocks is up nearly 15% year-to-date.
The Dow Jones industrial average was up 2.4%.
Microsoft, the world’s largest software company, said Wednesday it would offer a $10 discount to its customers who upgrade to Windows 7, 10, or 11, starting July 29.
It said the offer will apply to the entire United States, and that it would be valid for Mac and Windows computers.
Mac owners can upgrade to the new operating system from a Windows 8 or Windows 8.1 device that is compatible with Windows 7.
The Mac and Mac OS 10.10 version of the operating system also works with Windows 8 and Windows 8 Pro devices.
Microsoft said it will offer the discount on a one-time basis, and it will begin accepting applications for the discount, including Microsoft Office, Word, and Excel.
The discount is valid for the current quarter, the company noted.
The offer is subject to availability and will apply for a limited time.