Steven Sinofsky, the executive in charge of Microsoft's Windows 8 operating system is leaving the company, Microsoft announced late Monday, leading to speculations that the company could be dissatisfied with early sales of the operating system.

Windows and Windows Live President Steven Sinofsky will be leaving Microsoft and Julie Larson-Green will be promoted to lead all Windows software and hardware engineering, Microsoft announced today.

Sinofsky was the public face for Windows 8, posting constant updates in a Windows 8 blog that charted its development.

Sinofsky's departure is effective immediately, Microsoft said. The company will promote Julie Larson-Green to lead all Windows software and hardware engineering. Tami Reller retains her roles as chief financial officer and chief marketing officer and will assume responsibility for the business of Windows.

Microsoft says these changes are effective immediately and didn't say why Sinofsky left. Citing "a person with knowledge of the matter," Bloomberg reported that Microsoft had grown concerned over Sinofsky's ability to get along with other executives, including Chief Executive Officer Steve Ballmer.

"I am grateful for the many years of work that Steven has contributed to the company," Ballmer said. "The products and services we have delivered to the market in the past few months mark the launch of a new era at Microsoft. We've built an incredible foundation with new releases of Microsoft Office, Windows 8, Windows Phone 8, Microsoft Surface, Windows Server 2012 and 'Halo 4,' and great integration of services such as Bing, Skype and Xbox across all our products. To continue this success it is imperative that we continue to drive alignment across all Microsoft teams, and have more integrated and rapid development cycles for our offerings."

"It is impossible to count the blessings I have received over my years at Microsoft. I am humbled by the professionalism and generosity of everyone I have had the good fortune to work with at this awesome company," Sinofsky said.

Analysts speculated that the reasons for the split could include dissatisfaction with early Windows 8 sales and customer feedback.

Microsoft has so far been quiet about the sales performance of Windows 8 and of the company's Surface tablet. However, Ballmer admitted to French daily Le Parisien that Surface had a "modest" start to sales because of limited availability.