Windows 10 is not likely to be available to every eligible recipient upon its release date on July 29.

Microsoft said as much after pointing out the sheer volume of units angling to receive the new operating system. Microsoft placed the number of eligible Windows 10 recipients at around one billion, and given the astronomical figure, the company said the rollout may take more time, according to PC Mag.

The company has also provided a rough outline on who may receive the Windows 10 and when. Topping the proverbial Windows chain will be the Windows Insiders. These are the same users who secured their versions of the new operating system while they were testing it out during its beta phase.

After them will likely be the PC makers because are capable of installing the new operating system on new machines that have yet to be sold. Following that group will be the retailers, and Microsoft defended their spot in the hierarchy by saying most Windows 10 recipients would most likely approach them should they encounter any problems with their machines anyway.

Once those people have received their copies of Windows 10, the individual PC owners are presumed to be the only ones left on the list.

Terry Myerson, Microsoft's executive vice president for operating systems, also noted that even users who reserved their copies of Windows 10 may not be able to have it installed onto their units right away, according to The Register.

Myerson said not all units at present were capable of upgrading to Windows 10 with the current system they have running. Before those users can install the new operating system, they will first have to upgrade.

In addition, not all versions of Windows 10 will be available on July 29. Only Windows 10 and Windows 10 Pro will be released on that date, with the Windows 10 Enterprise and the Windows 10 Education set to be launched on August 1.