Welcome back to Linux Cloud and DevOps. This is the fourth course in the Linux Foundation specialization. In this module, we want to think about virtualization, where we're virtualizing a guest operating system in the Linux host operating system. We're running Linux, but we may be running another operating system underneath it. That can be Linux, that can be Windows, that can be something else. By the time we're done with this module, there's many things I want you to be able to do. This includes differentiating between different hypervisor types, I want you to be able to manage virtual machines on Linux, I want you to be able to describe Bootstrapping, and lastly I want you to be able to virtualize network connections. In this first lesson, let's think about hypervisor types. Type 1 hypervisors are often called bare-metal hypervisors. The hypervisor runs directly on the server hardware with no middle layer, middleman if you will. The hypervisor software interacts directly with the CPU, the memory and storage on the system, allocating them to each virtual machine as needed. Remember, an operating system normally does this. The operating system normally interacts with the CPU and memory and storage. But here, the hypervisor runs before an operating system, a Type 1 hypervisor. Some examples of Type 1 include Xen Server, KVM, VMware ESXi, and Microsoft Hyper-V. Two popular Type 1 Linux hypervisors are KVM, which is a Linux kernel-based virtual machine that uses a standard Linux kernel along with a special hypervisor module, and it can host any type of guest operating system. We also have the Xen Project, which is an open-source project for hardware virtualization, which includes additional software besides a hypervisor, for managing the hypervisor from the guest operating system. Type 2 hypervisors. These are commonly called hosted hypervisors because they run on top of an existing operating system. You first install an operating system, then you install the hypervisor or the Type 2 hypervisor. The hypervisor software runs like any other application on the host operating system. A couple of examples here are VirtualBox and VMware Workstation. In Type 2, host versus guest, we think about be, Linux can be either the host or the guest OS in a Type 2 hypervisor. When we think about running, Linux can run as a guest with another operating system as the host. Again, with running, Linux can run as the host with another operating system as the guest. Lastly, back to be, Linux can be both the host and the guest OS in Type 2 hypervisors. It's a lot to take in, so take a second to think about it. Little review here; Type 1 hypervisors run on the hardware, Type 2 hypervisors run on an installed operating system and VirtualBox is a Type 2 hypervisor that most use on top of Linux when they're trying to install some sort of hypervisor. See you in the next lesson.