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Understanding Windows Core OS and Microsoft's 'Polaris' for modern PCs

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MS logo (Image credit: Daniel Rubino / Windows Central)

Microsoft has big plans for Windows, and it involves stripping the OS down to its components, removing older legacy portions, and making it modular. Known as "Windows Core OS (WCOS)," the retooling will let Microsoft drive development faster and deliver new device experiences while maintaining the familiar look of Windows.

One aspect of Windows Core OS is referred to as "composers" – the user interface (UI) experience. Windows "Polaris" is one of those composers. Here is how it all fits together and why Microsoft sees this as the future of computing.

Window Core OS and OneCore

To understand how Microsoft's vision of Windows will work, it is essential to understand some of the OS architecture. Here's a list of key elements:

  • Windows OneCore – Microsoft successfully unified its kernel and OS core system across devices in 2015.
  • The Universal Windows Platform (UWP) – Microsoft unified its app platform, which runs on Win32 systems (x86, x64), ARM, and Xbox.
  • Windows Core OS – As reported by our Senior Writer Zac Bowden, Microsoft is making Windows 10 modular. Once finished, Windows 10 will look the same, but components like Win32 and telephony support for cellular calls can be added or removed easily by Microsoft. Windows Core OS will also pave the way for a true UWP-version of Windows 10 without any native Win32 support that will eventually supplant Windows 10 S.
  • Windows CShell – With the same kernel, a flexible core, and unified app platform, the last piece is the shell – or UI – that itself adapts to the screen. Taking the idea of Continuum to the OS level, CShell lets devices adjust their UIs for different tasks and experiences. A foldable mobile device would be able to scale between a phone-based UI and a tablet-based UI, and even extend into a desktop mode via Continuum, for example. Or, a Windows 10 PC could take on the Xbox UI when in gaming mode.

The idea here is simple: Windows will share the same kernel (OneCore) and now the same OS-level components (Windows Core OS), but the shell is variable and configurable based on the hardware being created.

Before this model, Microsoft had the unified kernel (OneCore), but the OS-level stuff was different across Windows 10 Mobile, Windows 10 PC, Xbox, HoloLens, and Surface Hub. Each one required its own team to maintain. While they all shared the kernel (OneCore) and app layer (UWP) the "middle" of each needed its own engineering team.

With Windows Core OS this model is killed off. The kernel, app layer and now OS-level components are all the same. The one difference will be the shell or the UI. In the Windows Core OS model, these are also referred to as "composers." For instance, there can be a tablet composer, one for desktop, and one for mobile.

Composers: Andromeda, Polaris, and more

Proposed OS structure of a device running "Polaris" and Windows Core OS.

Proposed OS structure of a device running "Polaris" and Windows Core OS.

Composers are part of the flexible shells that Windows Core OS will express. There is a mobile shell (Andromeda), desktop shell (Polaris), Surface Hub (Aruba), and mixed reality shell (Oasis).

New devices – in theory – could have multiple composers. For example, a device could act as mobile (Andromeda) but also shift to a desktop-mode (Polaris).

There could be even more composers – there are no limits. Microsoft would already have the kernel (OneCore), core OS (WCOS), and app layer (UWP) finished but it could drop in a new composer for a new type of experience, like gaming or collaboration mode.

Sound like Microsoft's Continuum experience juiced up? It is. This model is a form of Continuum built across all versions of Windows so that the OS can live on and adapt to new hardware without redoing the actual OS.

Simply put, Windows is now modular with the shell-level being the variable.

What makes a Polaris PC different?

The first time you see a Windows Core OS laptop running Polaris the software will look just like Windows 10.

Underneath, though, things are different. No longer are many legacy systems built into the OS, for example, the old File Explorer, or Fax machine. Legacy components are being gutted to streamline Windows for the next decade.

It is doubtful that all legacy systems are gone including some deeper hooks for "classic" Win32 APIs. Instead, think of Windows Core OS as a subset of the older, heavier Windows operating system.

But what about legacy apps? Microsoft has a few solutions reportedly under consideration. For one, Centennial bridged-apps from the Microsoft Store still run. Microsoft will likely put many of its own legacy apps into the Store as well to make up for their removal, like the old Microsoft Paint app.

Another solution may involve app-streaming – basically running your legacy app through the cloud to your device. But the real goal of Windows Core OS and Polaris for desktop and laptop users is UWP. Microsoft wants to get consumers using the Microsoft Store and apps on the UWP platform.

Windows Core OS: New device experiences only

Finally, it should be noted that Microsoft is not forcing Windows Core OS – whether Andromeda or Polaris – on anyone.

This streamlined version of Windows will only come to new PCs marketed with the leaner OS. In marketing talk, this is referred to audience targeting. Even then, consumers are likely not the first target. Instead, it will be positioned in the education market, including primary and secondary schools, first-line workers (FLW) and information workers.

There will also eventually probably be new consumer laptops and devices running this OS, like the new Always Connected PCs running Windows 10 on ARM. It is safe to say that future Always Connected PCs running Snapdragon processors will eventually come with Windows Core OS. They will have a lean, modern PC OS that has 4G LTE connectivity, instant-on abilities, and battery life that lasts weeks.

Windows 10 S is also likely to be supplanted by Windows Core OS and Polaris.

None of this is to say that Windows 10 Pro will be retired. Many companies, hospitals, governments, and even pro-level consumers need all that legacy support for desktops and laptops. Those devices will continue to be supported, and new hardware with it released.

But long-term, Microsoft sees Windows Core OS as the primary play for desktop, mobile, gaming consoles, mixed reality, and ambient displays (Surface Hub-like devices).

Why Windows Core OS is the right move

Windows Core OS is the right model for computing going forward. Google's Chromebooks are gaining market share – mostly in schools – but also for consumers (see this recent ZDNet article). The idea of a light, flexible, secure and utterly modern OS is needed for Microsoft if Windows is to have a future in the next decade.

The consumer market is headed towards a more mobile future. Google is selling its Chromebooks with the tagline "If you wish computers were more like phones." There's a very good reason why that message resonates, and if you have not yet figured it out, it's because you not paying enough attention.

Windows Core OS with its composers (Cshell) is the bridge to that future. For students, workers out in the field, ambient computing, and even the majority of consumers, such a model is the one taking hold. While there are a lot of questions about the future of Windows, this new architecture looks promising.

Daniel Rubino
Executive Editor

Daniel Rubino is the Executive Editor of Windows Central, head reviewer, podcast co-host, and analyst. He has been covering Microsoft here since 2007, back when this site was called WMExperts (and later Windows Phone Central). His interests include Windows, Microsoft Surface, laptops, next-gen computing, and arguing with people on the internet.

  • I honestly like this. It's basically one OS that's unified and offers different features on different devices. Only thing is I hope the shell is consistent. Kinda irritated with it right now.
  • Yep, MSFT is way ahead of unifying the OS where the others lag today.
  • I said all of this months ago...
    One Windows that's "Modular", and can adapt to any form factor..
    Adaptation may be a set composition of W10COS, or adaptation may be allowed to happen on the fly, in real-time, as the device itself modulates. It all depends on the type, size, configuration, and purpose of the device.
    Composition Desktop
    Composition Mobile portrait
    Composition Mobile landscape
    Composition Mobile Multi screen
    Composition Laptop
    Composition 2/1
    Composition infotainment
    Composition IOT
    Composition Retail
    Composition user customizable..... All the same One Windows10
  • And it's going to take years to get it right
  • And, by then, the world will have moved on.
  • Right.. Boeing is gonna design the next UCAV with Chrome OS, or iOS, using an iPad pro... Sure🙄
  • hahah
  • So Microsoft is going to scrap Windows 10 S, too?!?
  • Are you slow? Windows 10 is modular. MS can make adjustments when, and as they see fit. W10S is but a stepping stone. Quit trolling
  • Soo, now they call it modular to try to avoid people saying they scrap things :))) PATHETIC!!! MS idiots.
  • Thanks Zac and Dan for explaining Core OS and Polaris.  After watching your video I agree with WinOMG that this is a good idea.  It's a crying shame though that MS is playing such catchup with iOS and Android though.  By the time Polaris gets here (in probably LATE 2019) will there by be ANY consumers left on planet earth that haven't already switched to the iOS and Andorid ecosystems?  Especially seeing that MS has basically abandon-wared Win 10 mobile and now Windows S in the meantime.  Driving its last loyal fanbase and developer commuity into a panic, and forcing us to all wait in anxious suspense for the next "new shiny object" to chase. Also, I hope that MS will put as much effort into its App Store as it is putting into its new OS.  Sure, Itunes on UWP will be a win.  But there are still HUGE app gaps on the store.  Case in point Personal Finance: Where is Mint?  Where is any major bank?  Where is any major Credit Card company?  Sure, you can use a browser.  But really?  Sorry, but for many people browsers feel "old school".  They feel 1998, not 2018. Microsoft could help itself and its customers by kicking it's internal UWP app development in gear.  Personal finance case in point... resurrect MS Money as a UWP app.  Go head to head with Quickbooks and Mint.  Create a sister Win32 version and bundle it with Office 365.  Heck, create iOS and Android versions and sign those people up for Office 365 with MS Money too.  But start with UWP.  Show its fanbase and the developer community that MS itself is committed to UWP.  Instead what do we hear from Redmond... crickets. Bottom line... Polaris is a great idea, no question.  But it will be too little too late if MS doesn't throw the full weight of its resources and marketing into the App Store.  Because it all centers around the App Store experience for most light-weight OS users NOT THE BROWSER.  And as much as I hate to say this (because I love Edge), but especially not the Edge browser, which is the only browser available right now for Win 10 S... and I'm assuming Core OS.  
  • Playing catchup? Explain
  • Too much for you to understand?? Rodney fanbaby?
  • Now that Windows Mobile is dead, its time to get rid of UWP and revert Windows back to its true form.
  • I'm sure someone can sell you a copy of Win7
  • They might be better off with Windows 3.1 instead, none of that modern 32-bit crap that Windows 95 onwards added to get in the way :D
  • The problem with UWP is that was never a viable replacement for Win32 developers, far too limited in function and lacking even in basic areas. Who does Microsoft think is going to make software for this future UWP only operating system, they are smoking only the finest crack to be this delusional. Look at the years wasted with UWP and little to show for it, there is no interest in UWP amoung the people who still make software for Windows. For MS's Windows Core UWP only strategy to work they need a huge mega hit that rivals the iPhone, that is never going to happen. What is going to happen is that these gimped/modern versions of Windows will be met with contempt and disdain, no-one will touch them because thats not the reason people use Windows, consumers will be told to avoid them by everyone. It's the deaf leading the blind at MS.
  • Just like they were told to avoid Mac?  and then were told to avoid Chromebooks?  Yeah, that worked out really well....  
  • Even today, the Universal Windows Platform is under development and is improved with each Redstone release, adding more features, APIs and more. Today UWP can't remplace Win32, but Microsoft is working for make it possible in the future.
  • Why do closed minded people like you continue to post? Win32 is legacy even if it's more dominant than UWP. I believe that will continue to be the case for the next couple of years at least. Unlike you, Microsoft is looking towards the future and is building a new platform to accommodate that. UWP will continue to be developed for the next decade plus while Win32 will become a legacy platform that is not updated. 
  • But when Win32 dies, Windows may die with it. Is there any reason to use Windows outside of Win32? UWP certainly hasn't caught on at all. If Windows future is dependant on UWP, it isn't looking good.
  • as a deplovers my self can not more that agree UWP is to far limitation compire to Win32, but that is a explation for that, Win16 was borin in Win 3.1 and Win32 into Windows XP, so they have ben had like 23 year to build up the API for Win32, when UWP only had like 3 year to build the API is not gonna be a fast way build up all API into UWP some Win32 has in a short time, problie gonna take atlest 5-10 more years with only 2 update per year. For remove the limitation of UWP compire to Win32.  Darkness690 if you was a real software deplovers you should know what we dont like limitation you should be possibol to do what ever you want only you mind should be possibol to stop you frome do it and need more teching and learn build more for do the job.  You dont want to get stopped frome build stuff becouse is dosent support it.  If i want to build a software but some OS or device dosent allow me to build it, am just spend the time to build it for another OS, that is the cashe in here. Microsoft has not give the tools need for make UWP and modern stuff a chance to surirvel, dont blame the software deplovements blame it one Microsoft. 
  • I agree.  We absolutely need a Surface Phone, or at least a mini Surface Note (with GPS, motion sensor and LTE).  The abandonment of Win 10 mobile, and now Win 10 S, and now this whole Core OS re-write of them only seems to put that dream further and further into the future.  By the time it ever gets here there will be no light-weight consumers left on earth who haven't already switched to the iOS and Android ecosystems?
  • You didn't read the article, I see.
  • Thank you. Many people seem to be confused. This might help.
  • Informative, thanks
  • Good read. This clarified a lot for me.
  • ..The break down. Thanks Dan!
  • So, in order to appreciate what the hell is Microsoft doing, we need to untangle that mess. And it is highly possible that after understanding the whole idea, it will be already dead. Why not make a freaking OS that just works, and stop confusing consumers with all that chitchat, versions, editions, releases, builds, etc?
  • The average consumer doesn't have to understand any of this. This article is for enthusiasts and techies.
  • Are you sure? The legacy-less Windows is not a new concept. Actually, it was part of Windows RT's philosophy, and yet people was confused as hell when they failed to run regular Win32 apps on Windows RT. So, how should I explain the "advantage" of not being able to run legacy apps to average non-techies customers without getting too technical?  
  • Apparently you didn't read the article it will have a legacy component that is modular instead of being integrated into the OS. This is no different than the technologies in Windows 10 Enterprise 1709 such as device guard and app guard where they take components out of the OS and compartmentalize them into virtual spaces. Device guard does that to the kernel and app guard does it to edge.
  • But... That's what they are doing...
  • No it isn't. They are making it complicated. You will have to go into the store and know what version of Windows you want. If you get the wrong one, it isn't going to do what you need. It is Windows RT all over again. They need to stop with this RT nonsense. People don't want it. If Microsoft insists on this path, they need to rename it. Leave the Windows name for classic Windows experiences. Stop confusing people.
  • Amen brother!!
  • Indeed.
  • Are you that easily confused? 
  • Here we go with the hip shooting again. It's a modular OS to the consumer it isn't going to be any different than what they are used to. Plus most consumers just use Windows media consumption, word processing, social media, and web browsing so how are they going to miss what they don't use. There will be an optional legacy app component that can be added in. I mean how is this any different than Windows 7 basic? It was a nerfed home that had limited capabilities. It's not RT because RT couldn't do anything outside of the store
    this OS has the ability to do things outside of the store you would just need the OS module for it.
  • "You will have to go into the store and know what version of Windows you want. "
    With Win32 app support via containers/emulation and/or streaming the consumer won't know the difference. They'll see "Windows" just faster, lighter, better battery life. No need to bring this up to consumers (which won't happen for awhile anyway). Regardless, you still need to explain how Microsoft is to maintain Windows yet make it relevant for the next decade. Keeping the OS "as is" is a road to failure. This is only complicated because we're telling you what is happening internally. Consumers don't care about this stuff, don't need to know about "composers" or app layers, APIs, etc. Never have, never will.
  • Most people consumers dont need win32 apps. But professional instead need win32 registry for network app communication. So i would like to see somethike like Microsoft windows for  advanced workstation that is a plugin that you get throught the store. Maybe download win32 legacy support from the windows store. there somany apps outthere that still need win 32. NLE DAW CAM CAD IDE SCADA Projection mapping and many apps still use win 32 api many people wrote code with win32 in mind ex: audio software pligins Even office in win32 is supperior to his UWP counterpart. UWP is for most home users but sometimes people would like to run a specific software that will be written for win 32 ex: a father who want to edit a small family memory video with a cheap video editing software
  • Consumers who don't need Win32 don't need Windows. Period. Moving away from Win32 is the wrong direction for Windows. If Microsoft wants something new, they need to build something new.
  • Did Apple marry themselves to OSX? Were they worried about how to keep it relevant for the next decade? Did they try to shoehorn it on an iPad? No. They started fresh and made something new and exciting. They didn't limp along dragging a 30 year old anchor while wondering why they are so far behind the competition. Windows has been holding Microsoft back.
  • Yes It seems they are being masochisitic and have taken on an unbelivably hard engineering challenge :)  However, I think Google is working on something like this - one OS for they have to do this?  I wish they would get rid of the windows name for consumer market and come up with some new and exciting branding!    If my wish comes true Windows Central also has to change it name! So Dan & co are going to downvote my comment :)
  • Read your comment again bleached.  OSX IS a boat anchor.  It has close to no market share,  it's old, clunky and terrible to use as a consumer.  Graphics professionals are moving to windows and the studio line up because they offer time saving value.  
  • Everyone makes mistakes including Microsoft, Apple and Google...
  • Every company makes mistakes, but MS is the king of failures and lies. They are an embarassment to the tech world.
  • Composers should be made open source and allow different OEMs to bring their own UX/UI. Problem android?
  • No thanks. Is enough awful on Android, keep Windows far from this.
  • Microsoft must be ready to go it alone then. The manufacturers really embraced this with Android and it worked out quite well for them. Android now outsells Windows 5 to 1. Microsoft could still have their own UI while allowing the OEMs to innovate with their devices.
  • The reason why Android is a total security disaster is because of open source. 
  • all this is useless if the UWP developer experience is not vastly improved to where there are virtually no API limits as to what can be programmed.
  • Including Malware?  So they should allow the system to be completely open so that anyone can write the next exploit for something like Spectre or Meltdown?  How about Rowhammer?   There is a reason why on large computers, "system" programming was always separated from "Application" programming.
  • I was never confused in the first place. I knew what they were doing, I simply disagreed with some of it, and vehemently disagreed with a lot of how they were choosing to go there.  But I'm the outlier. I'm not the target demographic. I'm the extreme minority that understood the Metro experience and loved it, understood Hubs and their potential, appreciated that VERY touch-friendly approach that still allowed for full legacy desktop support.  I'm the minority that does music arranging & recording, video editing and understands these high-power legacy programs place demands on a system the Polaris, et al, will likely never be able to address.   Yes, I love the idea of a fully adaptable single platform.  I'm not against that.  That part I agree with.  But Microsoft has built a HUGE reputation of enticing us with great ideas and promises, stringing us along and then yanking the rug out from under us and giving us lame answers like Jason's "things change".  To which I just say "bite me".  It would serve Microsoft right if they blew this Next Big Thing again and finally lost everything to Apple and Google.  As much as I hate Apple and Google, I'm at the point where Microsoft deserves to finally fail.
  • This is the truest comment you've posted I can remember. I too feel like MS is just going to keep screwing thepooch
  • +1000 Unlike many I am a huge fan of Windows 8.  It's shame Microsoft was frighened away from a beautiful concept.  I'll use it until my main computers fall apart.  
  • So why aren't they there yet? They've given up on Windows Mobile for a long time now & still lack ' what's next ' out in the market. My L950XL isn't going to last forever, & so far MS has had no plan to bridge users over, except get this, making Google Android(whom they are trying to compete with) feel a little more like a MS experience. They really need to hit some sort of goal that resonates with users.
  • The predicament that MS finds itself in, is an interesting one. If they broke it down, I don't think they make that much money on Windows OS anymore. I am assuming that the majority if their growth, and profits are based on MS cloud, and Office 365 subscriptions. Me, personally, I've paid MS more on my yearly 365 subscription, in the last 3 years than I have ever (other than the 1 time purchase of my SP3 like 3.5 years ago..........bottom line, I think that even if Windows goes away, which will be a long time from now, too many professionals out there need the software, and security to give it up.......they will still make boatloads of cash on their other ventures.
  • It will be interesting to see what new form factors will come out of this. Thanks for clearing this up Dan.
  • So, just to see if I got it right: Windows 10 Core will essentially be the base SKU of Windows, completely rewritten in UWP and only running UWP apps natively, correct? In that case, some questions: 1) Will Home, Pro, Enterprise, etc SKUs be Windows 10 Core with Win32 subsystem included? Because while I want to see Microsoft fully port the Shell, File Explorer, Task Manager and other OS elements into UWP I'm not ready to give up running Win32 apps natively, and may never be. 2) What is the schedule regarding porting Microsoft's own major apps fully to UWP? Because while the company may consider Centennial Win32 apps to be UWP my understanding is that they're more like hybrid beasts that run both Win32 and UWP code, thus their legacy look and feel. That means that out of all Office apps only Store OneNote is fully UWP, with the others essentially only pretenders. And then there's Visual Studio, which hasn't even been desktop bridged yet to my knowledge. 3) Does Adobe, Corel, Autodesk and other major companies have any ongoing plans regarding porting their major apps to UWP?  My concern here is that it seems a year from now we'll be entering a world where the Windows that'll be the focus of Microsoft will be the one that runs UWP and only UWP and the major fully UWP apps that we can name are OneNote and Adobe XD. That concerning, to say the least.
  • First, UWP apps runs natively even today, thanks to the WinCore OS. But with Polaris, all the OS will be based on UWP for better performance and energetic efficency. Also, is mentioned that the actual versions like Pro, Enterprise, etc, will exist like today, but possibly things like UWP file explorer will be added, thanks to Cshell and Redstone 5(?) development. Also, do not forget that Polaris will have someday some type of Win32 support, but yeah, i want to see Adobe for example, fully suporting UWP. But i think that Microsoft must to improve the WinRT/OneCore OS first.
  • next give shell AI touch, integrate cortana into shell...:)
  • I like modular way better.  .net was modular from 1.0 to 4.0, so you could chose not install a version if you didn't need it and new version didn't mess with old versions.  Around 2011-2012 they started contious improvement of 4.0 which meant that obsolete portions could never drop off.  If a new version broke your old software, then you were stuck as your only resolution was to never move forward or try to find get the contractor back to fix the software.  I hope they are going modular for everything. They could do stuff like install the uwp module on windows 7 if they wanted 
  • Windows will be dead by the time we take profits from this. No mobile, no future.
  • Andromeda? 
  • I heard this back in 2012 too. iPads were supposed to replace laptops. How'd that go?
  • Daniel,  to be fair,  They have replaced laptops for ALOT of users.  Power users,  NOPE.  but for the average facebook dweller.  They 100% have replaced laptops.  
  • Dan to the rescue, thanks for this thorough article.
  • This is all find and good but will app developers and OEMs support it??  Right now app developers are continuing to focus on Android and iOS. Look at how there is already a new app gap with Cortana. Microsoft needs to develop a device that will entice app developers back to their platform. If Microsoft doesn't have the apps, they are doomed.  
  • Hence why they have Andromeda, Windows Core OS and Polaris. However the future of Mobile development is moving towards PWA, which Microsoft is already moving towards, so in the future Microsoft will simply scan the web for PWAs and add them into the Store. 
  • In a world of PWAs, why would you need anything but Chrome?
  • Because some people would rather stay away from Google products?
  • Is that a large number of people or just some Microsoft fanboys?
  • It's no longer about OSes anymore in the age of PWA, it's about ecosystem and what specific things that OS offers that PWAs can't do. Windows 10 is obviously Win32 and it's diversity. That'll be still be there, however With Polaris and Windows 10 Pro S Mode, it's clear that MS Store is where the future is.
  • For the last years, that futuristic App Store has been nothing but a junk, pardon me for not being so delusional.
  • Well, get back to me when a PWA can be used to play Crysis!!!
  • Nice article Dan. This ne