On Wednesday this week, virtualisation behemoth VMWare published a security advisory describing two just-patched security holes in its products.

Virtualisation in general, and VMWare’s product set in particular, is widely used to turn individual physical computers into several “virtual computers” that share the same physical hardware.

These virtual computers, known in the jargon as VMs (short for virtual machines), realistically pretend to be independent computers in their own right, each one booting and running an operating system of its own, as a physical computer would.

This means that one physical server, located in an on-site server room or in a cloud data centre, can flexibly be divvied up amongst multiple different users, who could come from separate departments in one organisation, or even from different companies.

Each user gets access to what looks like, feels like, and runs like a computer of all their own, with an operating system and application stack of their own choice.

Each VM, known in the jargon as a guest, has its own virtual hard disks, stored as a regular files on the physical server, known as the host.

This means you can not only divide up one physical disk array into a variety of differently-sized guest disks, to suit the varying needs of the various guest users, but also easily snapshot and archive entire VMs by copying their virtual disk files.

You can even clone an existing VM, and migrate the files that store its content to another physical server, in order to adapt quickly to rising demand for service or to recover from regional outages.