# Release 1.2 (2012-12-06)

This release has the following improvements and changes:

  - Nix has a new binary substituter mechanism: the *binary cache*. A
    binary cache contains pre-built binaries of Nix packages. Whenever
    Nix wants to build a missing Nix store path, it will check a set of
    binary caches to see if any of them has a pre-built binary of that
    path. The configuration setting `binary-caches` contains a list of
    URLs of binary caches. For instance, doing
    
        $ nix-env -i thunderbird --option binary-caches http://cache.nixos.org
    
    will install Thunderbird and its dependencies, using the available
    pre-built binaries in <http://cache.nixos.org>. The main advantage
    over the old “manifest”-based method of getting pre-built binaries
    is that you don’t have to worry about your manifest being in sync
    with the Nix expressions you’re installing from; i.e., you don’t
    need to run `nix-pull` to update your manifest. It’s also more
    scalable because you don’t need to redownload a giant manifest file
    every time.
    
    A Nix channel can provide a binary cache URL that will be used
    automatically if you subscribe to that channel. If you use the
    Nixpkgs or NixOS channels (<http://nixos.org/channels>) you
    automatically get the cache <http://cache.nixos.org>.
    
    Binary caches are created using `nix-push`. For details on the
    operation and format of binary caches, see the `nix-push` manpage.
    More details are provided in [this nix-dev
    posting](https://nixos.org/nix-dev/2012-September/009826.html).

  - Multiple output support should now be usable. A derivation can
    declare that it wants to produce multiple store paths by saying
    something like
    
        outputs = [ "lib" "headers" "doc" ];
    
    This will cause Nix to pass the intended store path of each output
    to the builder through the environment variables `lib`, `headers`
    and `doc`. Other packages can refer to a specific output by
    referring to `pkg.output`, e.g.
    
        buildInputs = [ pkg.lib pkg.headers ];
    
    If you install a package with multiple outputs using `nix-env`, each
    output path will be symlinked into the user environment.