Why containers matter
Virtualization revolutionized server deployments. Instead of buying and installing a physical server for every SQL Server instance, one server, known as a hypervisor, could run multiple virtual machines (VMs) that virtualized the hardware and could have an OS installed inside of it. A VM is a software-defined representation of a physical server that provides agility for IT in a way that traditional hardware cannot.
A container is similar, yet different, and arguably the evolution of virtualization. Instead of virtualizing the host and managing it as you would a traditional physical server, such as installing software and patching the OS and applications, containers virtualize the OS, not the hardware. The abstraction is completely different and will be explained more in the Container technical fundamentals section.
While an OS is still required for a SQL Server container, the major difference is that the OS (specifically its kernel) is shared, or virtualized...