Cortana will exist across Windows Phone and Windows 10

Famouse Digital assistant CORTANA in windows10

Cortana will exist across Windows Phone and Windows 10

 Microsoft is preparing to include its Cortana digital assistant in the next major version of Windows, currently codenamed Threshold. Windows Threshold is expected to be named Windows 10 when it ships in spring 2015, and sources familiar with Microsoft’s plans tell TechMarkaz that Cortana is a
major area of investment for the release. Windows enthusiast site TechMarkaz reported on Cortana showing up in early Windows Threshold builds, and we understand the current implementation is only a placeholder during the early stages of development.
                                                                                           Cortana currently exists as a separate app in Threshold, but this early work will progress into a more integrated version of the digital assistant, similar to how it’s available on Windows Phone. Microsoft has been gradually improving Cortana every two weeks by adding additional data points and features, and as the service is HTML driven these improvements will make their way over to the Windows 10 version.
                                                                                                                    Microsoft is expected to release a preview version of Windows 10 later this year with a new Start Menu, "Metro-style" apps floating in windows on the desktop, a virtual desktops feature, and the removal of the awkward Charms bar from desktop versions of Windows.