Microsoft's Windows Subsystem for Linux is coming to all Windows 10 users (archive):
You won't have to be a tester to try Windows 10's new, built-in Linux kernel in the near future. Microsoft has confirmed that Windows Subsystem for Linux 2 will be widely available when Windows 10 version 2004 arrives. You'll have to install it manually for a "few months" until an update adds automatic installs and updates, but that's a small price to pay if you want Linux and Windows to coexist in peace and harmony. It'll be easier to set up, at least -- the kernel will now be delivered through Windows Update instead of forcing you to install an entire Windows image.
Embrace, Extend... Excite!
Windows blog post.
Previously: Windows 10 Will Soon Ship with a Full, Open Source, GPLed Linux Kernel
Windows doesn't support fork() or exec() natively. In order to emulate the behavior of fork(), cygwin has to jump through all sorts of hoops. It is a surprisingly complex operation. The context switches, mutexes, etc. produces a lot of overhead. Then if you call exec(), you end up causing another massive behavior emulation routine.