Hosted runners
We already used hosted runners in the previous chapter. Hosted runners are GitHub-hosted virtual machines that can be used to run your workflows. The runners are available for Linux, Windows, and macOS operating systems.
Isolation and privileges
Each job in a workflow executes in a fresh instance of the virtual machine and is completely isolated. You have full admin access (passwordless sudo on Linux), and the user account control (UAC) is disabled on Windows machines. That means you can install any tools you might need in your workflow (this just comes with the price of build time).
The runner can also access user interface (UI) elements. This enables you to execute UI tests such as Selenium inside the runner without the need to do this through another virtual machine.
Hardware
GitHub hosts Linux and Windows runners on Standard_DS2_v2 virtual machines in Microsoft Azure. The hardware specifications for Windows and Linux virtual machines are as follows...