How many people contribute to Linux kernel?

The Linux kernel, at over 8 million lines of code and well over 1000 contributors to each release, is one of the largest and most active free software projects in existence.

Does Microsoft contribute to Linux?

Microsoft is a member of not only the Linux Foundation but also the Linux kernel security mailing list (a rather more select community). Microsoft is submitting patches to the Linux kernel “to create a complete virtualisation stack with Linux and Microsoft hypervisor”.