Windows 10 20H1 Build Hits Insider Fast Ring With Native WSL 2 Linux Kernel

Windows 10 WLS 2 Linux
Hell has not frozen over and last I checked, there are no pigs flying overhead. However, the latest test build of Windows 10 (18917) does include a full Linux kernel, which brings about a key change to the way way Windows accesses and handles Linux files. Not to worry though, the change is for the better, resulting in improved performance.

The new Windows 10 build is available to participants of the Windows Insider program, who have opted for the Fast ring—this is the branch that receives test builds earlier in the development cycle than those that get pushed out to the Slow ring. As a result, they can be more buggy and "might be more painful for some."

In this new build, Microsoft includes the new Windows Subsystem for Linux 2 (WSL 2). The previous version, WSL 1, allowed users to run Bash in Ubuntu in Windows 10, but WSL 2 is a full Linux kernel, just as Microsoft promised back at its Build 2019 conference in May. It is a custom Linux kernel that Microsoft built, based on version 4.19 of Linux.

WSL 2 leverages Hyper-V features to operate in a virtual machine. With the previous WSL 1 implementation, Microsoft instructed users to place their Linux files on their C: drives. But for WSL 2, those files must now be placed in the Linux root file system, a change that enables better performance when accessing files.

"This new architecture, which uses a real Linux kernel, changes how these Linux binaries interact with Windows and your computer’s hardware, but still provides the same user experience as in WSL 1 (the current widely available version). WSL 2 delivers a much faster file system performance and full system call compatibility, which lets you run more applications like Docker!," Microsoft explains.

The "lightweight utility VM" launches at startup and chews up a small amount of memory, but Microsoft says it is only a small proportion of the user's total system memory, giving in an overall "small memory footprint." There a drawback with how WSL 2 is implemented, however. Microsoft notes that users will see slower file speeds compared to WSL 1 when accessing Windows files from a Linux application, and vice versa.

"This is a result of the architectural changes in WSL 2, and is something that the WSL team is actively investigating on how we can improve this experience," Microsoft states in a document outlining the changes between WSL 1 and WSL 2.

Outside of the improved Linux implementation, the latest test build contains a few other features and changes. Some of the notable ones include...
  • New download throttling options for Delivery Optimization
  • Data table reading improvements to Narrator
  • Windows Ink Workspace takes up less screen real estate
There is also the usual round of bug fixes, including one that was causing some users to see a 0x8007000E error code while the downloading the build due to high RAM consumption.
Microsoft only recently began pushing out its Windows 10 May Update to the general public. The company has committed to releasing two major "feature updates" to Windows 10 every year. Interestingly, Microsoft still has not begun testing the 19H2 release, which is due to arrive later this year. Windows journalist Mary Jo Foley surmises that it will be more of a service pack devoid of new features.

As for the test build with WSL 2, it will arrive in polished form in the first half of next year.