As the proprietary and open-source systems battle for mobile and PC users, what are the prospects for these two champions of converged computing?
As sales of tablets and phones continue to outstrip demand for PCs, the technology industry is preparing for a shift in how people use computers.
The expectation is that phones and tablets will begin to be used as desktop PCs, a change that will force a fundamental redesign of software.
Instead of operating systems and applications having a single interface, apps will alter their look and controls to reflect how they are being used. For example, a UI that favours large, easily-tappable buttons on a touchscreen tablet might switch to tightly-packed icons when the tablet is docked and being used with a monitor and a mouse.
The idea was dubbed convergence by Canonical, the company behind the Ubuntu operating system, when it launched the idea for a phone that would double as a PC in 2013.
The crowdfunding campaign for the Ubuntu Edge phone failed, but Canonical remains committed to transforming Ubuntu into an OS that adapts its interface according to its use.
Windows 10 will feature Continuum mode, which will detect when mobile devices are docked with a mouse and keyboard and reorient the UI to suit. The other major feature will be support for what Microsoft calls universal apps, applications that share their core code but that can switch their interface to be equally usable on desktops, phones, tablets and even augmented reality headsets.
With both Windows and Ubuntu being remodelled around convergence, how are both likely to fare as Microsoft and Canonical bid to be at the vanguard of the next wave of computing?
Hardware expertise: Microsoft's $7.2bn acquisition of Finnish handset maker Nokia gives it a hardware arm that can produce phones and tablets that show off the capabilities of Windows 10.
Redmond is reportedly working on two high-end phones that will act as a flagship for the OS - with top-of-the-range specs, including a 5.7-inch QHD display, Qualcomm octa-core processor, 3GB of RAM, and a 20-megapixel camera.
In contrast, the first Ubuntu phone to appear had fairly middling hardware, comparable to a mid-range Android device. And in a speech on Monday, Canonical CEO Mark Shuttleworth also confirmed that the first Ubuntu handset to offer a converged phone-desktop OS would not be the "biggest, baddest workstation".
More features: Beyond the promise of apps that scale their interface to suit many different sized-devices, Windows 10 will integrate additional services and control schemes that work across desktops and mobile.
Chief among these cross-platform services is Cortana, Microsoft's virtual assistant that can set appointments, search for information and answer rudimentary queries.
With its universal apps platform, Microsoft also seems to be providing a toolkit for designing software whose interface will tailor its controls and appearance to suit a wide range of devices.
That name recognition might persuade those looking for a mobile device to replace their desktop to stick with what they know - particularly among enterprises where the Windows brand is still strong.
As well known as Ubuntu is in Linux circles, it has very little desktop penetration, with Linux-based operating systems as a whole accounting for just over one percent of PC users worldwide.
Control over flagship software: Microsoft has the advantage of developing Windows marquee software titles, such as its Office suite.
This in-house control has allowed Microsoft to redesign Microsoft Office as touch-friendly universal apps.
In contrast, Canonical doesn't have the same internal control over development of key software on Ubuntu, with its developers numbering among the many contributors to major open-source software such as LibreOffice.
Open to iPhone and Android apps: At its recent Build conference, Microsoft announced plans that it hopes will bring iPhone and Android apps to Windows 10.
Developers will be able to port iOS and Android applications to Windows 10 without the need to rewrite the bulk of the code.
By opening the door to the millions of applications running on the world's most popular mobile platforms, Microsoft has bolstered Windows 10's chances of having the apps that users want.
First to market? It seems Ubuntu may beat Windows 10 and be the first converged PC-phone operating system out of the door.
The first Ubuntu phone that doubles as a desktop will be "released this year", according to an announcement by Canonical's Shuttleworth this week.
That could place the open-source OS ahead of Windows 10. Microsoft is expected to release Windows 10 on x86 PCs and tablets in July this year but will launch the OS on phones, small tablets, Xbox, and Hololens at unspecified later dates.
However, Canonical has previously missed dates for delivering a converged Ubuntu OS.
Price: The first Ubuntu phone to launch was the relatively modestly-priced Aquaris E4.5 Ubuntu Edition smartphone.
Shuttleworth has said the first Ubuntu phone to run as a phone and a desktop PC will be suited to casual rather than power users. While these so-so specs might be a deterrent to some, they could also indicate a price sufficiently low to tempt people to give it a try - particularly if its performance is good enough to meet their needs.
Novel UI: Ubuntu blurs the line between online and local content and demonstrates a bold direction for a converged Ubuntu OS.
This approach is particularly apparent on Ubuntu phones, where the OS is built around Scopes - full-screen menus that group together related content of interest to you. This content can be stored on the phone or available via online services. For example, a music Scope would show music on your phone, on the SoundCloud music-sharing or the GrooveShark music-streaming services and on YouTube, with each section able to expand into an app to play music or explore more tracks.
Organising an operating system around the interests of the user and ignoring the distinction between online and offline content shows how future Ubuntu releases could go a step beyond the dynamic content Windows 10 will offer with its Live Tiles.
Abundance of open-source apps: Although the appeal of open source goes far beyond getting software for nothing, the wide range of high-quality, free open-source software that runs on Linux operating systems can't be ignored.
While many of the bigger open-source projects also run on Windows, Ubuntu comes with an abundance of free software that can downloaded directly from the Dash desktop search or the terminal.
Customisable: With Windows, to a large extent you're stuck with the operating system that Microsoft gives you.
With Ubuntu, like other Linux distros, if you don't like something about the operating system, you can generally swap it out with a few terminal commands.
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