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# Arvo source

When you boot an Urbit we transfer the current version of the Arvo operating environment to your Urbit over our network.  That is, the source for the system lives on your Urbit.  Here we'll take a brief tour through the structure of a base Arvo desk.  

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Looking at the top level of [the Arvo repo](http://github.com/urbit/arvo), or any Urbit desk that has been mounted to Unix we see something like:

    app/
    arvo/
    gen/
    lib/
    mar/
    ren/
    sec/
    sur/
    web/
    web.md

Let's step through directory by directory.

## `app/`

This is where Gall apps live.  Gall apps are stateful servers, sort of like unix daemons.  One familiar one is `app/talk.hoon` which is the source code for Talk the urbit messaging transport layer.  And there's also `app/dojo.hoon` — that's your shell.

## `arvo/`

This is where the Arvo vanes live.  Vanes are sort of like kernel modules. These are worth listing one by one:

### `arvo/ames.hoon`

Ames is our network protocol.

### `arvo/behn.hoon`

Behn is a simple timer.

### `arvo/clay.hoon`

Clay is our filesystem.

### `arvo/dill.hoon`

Dill is our terminal driver.

### `arvo/eyre.hoon`

Eyre is our webserver.

### `arvo/ford.hoon`

Ford is our build system.

### `arvo/gall.hoon`

Gall is our application model.

### `arvo/hoon.hoon`

Hoon is our programming langauge.  Since Hoon compiles itself the language is actually specified in this source file.

### `arvo/zuse.hoon`

Zuse is the Hoon library.  

That's it.  That's the whole system.

## `gen/`

`gen/` holds generators.  Generators are short Dojo scripts.

## `lib/`

`lib/` holds shared libraries for programs. `lib/sole` is a good example — that's the console library that's shared by both Dojo in the command line, and the Dojo web client.

## `mar/`

This is where marks live.  Marks are data type definitions used by Ford.  A mark is like a mime-type, but specified in executable code.  

## `ren/`

These are web renderers.  A renderer handles web requests of a particular type.  

Default web requests in urbit are handled as a `.urb`, which is caught by the `urb.hoon` renderer.  This wraps the request in our default `css` and `js` and adds some routing magic for certain paths.

## `sur/`

`sur/` contains shared data structures.  Files in `sur` are like header files in C.

## `web/`

There are the files publicly accessible to the web, as made possible by Eyre.

## `web.md`

This is the homepage for your urbit.  You'll see it at `http://localhost:8080/` or `http://fintud-macrep.urbit.org/`.