PC users hoping to have Windows 10 running on their machines on July 29 may have to wait a little longer, with Microsoft revealing it will now phase in availability of the new operating system.

Operating systems boss Terry Myerson said in a blog post that only Windows Insiders – the five million-odd users in the vendor’s official beta program – should expect to start seeing the completed Windows 10 from the official launch day.

Consumers who reserved their free upgrade will be notified “in waves”.

Microsoft did not say how big those waves would be, but did reveal that "millions" of reservations had been received.

The waves appear dependent on whether Microsoft has finished validating Windows 10 to run on your particular hardware configuration.

“If you reserved your copy of Windows 10, we will notify you once our compatibility work confirms you will have a great experience, and Windows 10 has been downloaded on your system,” Myerson said.

“If your system is not ready yet for your upgrade to Windows 10, we will provide more details during the upgrade experience.

“In some cases, we will include contact information so you can follow up directly with an application provider or device manufacturer to learn more.”

Myerson said compatibility testing was ongoing.

“In our testing of millions of systems, we’re seeing full compatibility today with the vast majority of Windows 8x and Windows 7x systems – and we are not yet done,” he said.

“We will be continuing this application and device compatibility work every day as part of our ongoing commitment to Windows as a service.”

Users whose machines were not completely compatible with Windows 10 would still be offered a chance to switch to the new OS. Myerson said. Such users could consider buying “alternative compatible solutions in the Windows Store after [the] upgrade”.

For business and enterprise users, Windows 10 Pro will be made available on launch day.

However, Microsoft noted that “volume licensing customers will be able to download Windows 10 Enterprise and Windows 10 Education … starting on August 1".

[Read: Five talking points for business on Windows 10]

Microsoft also said it would provide an OEM build to computer makers shortly, as well as a build that retailers can offer customers who purchase older Windows 8.1-imaged computers.

The staged rollout of Windows 10 could be sensible given lingering concerns over the state of the operating system in the lead-up to its July 29 official launch.

“Windows 10 will of course be ready for July 29th, but how complete and stable it will be could vary depending on your hardware and usage,” The Verge’s Windows expert Tom Warren noted last month.

“A few weeks doesn’t seem like enough time right now, especially given the current state of Windows 10."