The Physiome Model Repository (PMR) site is a web accessible repository of models which includes the CellML and FieldML repositories. (Note: the PMR site is powered by software called the PMR Software. Usually the term PMR will be referring to the PMR site, but if clarification is needed, "PMR site" will be used. It is also sometimes referred to as a "PMR instance", since it is possible to create other sites running the PMR Software, i.e. other instances.)
PMR relies on the distributed version control system Mercurial (Hg), which allows the repository to maintain a complete history of all changes made to every file contained within repository workspaces. In order to use the Physiome Model Repository, you will need to obtain a Mercurial client for your operating system, and become familiar with the basic functions of Mercurial. There are many excellent resources available on the internet, such as Mercurial, the definitive guide. Mercurial clients may be downloaded from the Mercurial website, which also provides documentation on Mercurial usage. A graphical alternative to a command-line client is available for Windows, called TortoiseHg. This provides a Windows explorer integrated system for working with Mercurial repositories.