Video and slides synchronized, mp3 and slide download available at URL http://bit.ly/1LfBmUn. Anil Madhavapeddy explains how the OCaml module system enables the construction of a large scale OS software, and also the resulting portability benefits. The talk is given from a low-power ARM board running Mirage, and the same logic can also be compiled into JavaScript, kernel modules or Unix binaries. Filmed at qconlondon.com. Anil Madhavapeddy is a Senior Research Fellow at the University of Cambridge, based in the Systems Research Group. He was on the original team that developed the Xen hypervisor, and helped develop an industry-leading cloud management toolstack written entirely in OCaml.