The company is "still not sure if (computer manufacturers) will be able to ship Vista once Windows 7 is made available," General Manager Richard Francis wrote in a recent e-mail, IDG News reported Monday.
Microsoft customers complained that the Vista system was slow and included cumbersome prompts that required granting permission for various tasks.
Last week, Microsoft released the preliminary version of Windows 7, allowing customers to test-drive the system. It is the last stage of development before the company padlocks the code that will be shipped to computer companies, IDG reported.
Microsoft, meanwhile, appears ready to allow Vista to fade into obscurity.
"It's been a long time since we've had a version of Windows that will actually run better (than the previous version) on the hardware that most customers have," said Mike Nash, vice president of the Windows product management group at Microsoft, during a recent conference call.
Customers who purchase a PC with Windows 7 pre-installed will be allowed to downgrade to Vista," Francis said.