Describe save states.

docs/concepts/save-states.md

@@ -1,11 +1,129 @@
-TODO
+A real game console
+is a complex piece of hardware,
+with electricity flowing through it
+in complex patterns that can't easily
+be paused or recorded.
+However,
+an emulated console is pure software:
+it only changes when the emulation software
+deliberately updates it,
+so the emulator software can save
+the entire state of the emulated console
+to disk,
+and weeks or months later
+bring it back to life
+as though nothing had ever happened.
 
 Save states versus in-game saves
 --------------------------------
 
+Some games include their own systems
+for saving and restoring the player's progress.
+Here are some of the differences
+between save states and in-game saves:
+
+<table>
+<thead>
+<tr>
+<th>Save states</th>
+<th>In-game saves</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+	<td>
+	Work exactly the same way
+	in every game
+	</td>
+	<td>
+	Works differently in different games,
+	some games don't support it at all
+	</td>
+</tr>
+<tr>
+	<td>
+	Save at any time,
+	anywhere in the game
+	</td>
+	<td>
+	Save only at special save-points
+	</td>
+</tr>
+<tr>
+	<td>
+	Loading a save
+	puts the game back exactly how it was
+	when you pressed save
+	</td>
+	<td>
+	Loading a save
+	restores some things
+	(like the player's inventory
+	or remaining lives),
+	but may
+	forget others
+	(like taking you back to the beginning of the level)
+	</td>
+</tr>
+<tr>
+	<td>
+	You can have dozens of save states
+	</td>
+	<td>
+	Most games limit you to about 3 saves
+	</td>
+</tr>
+<tr>
+	<td>
+	Can only be loaded
+	by the same version of the same emulator
+	that created it
+	</td>
+	<td>
+	Works with any version of any emulator,
+	can sometimes even be copied to or from physical cartridges
+	</td>
+</tr>
+</tbody>
+</table>
+
+**Note:**
+Loading a save state
+will reset the entire emulated console
+to the way it was when the save state was created,
+*including in-game saves*.
+If you create a save state,
+then make an in-game save,
+then load the save state,
+**your in-game save will be lost**.
+Don't do that.
+
 Quick states
 ------------
 
+higan has five Quick State slots,
+which can be used from
+[the Tools menu](../interface/higan.md#the-tools-menu),
+or with the appropriate
+[hotkeys](../interface/higan-config.md#hotkeys).
+
+Quick states are useful
+as extra checkpoints
+in games that don't have them,
+or where they aren't close enough together.
+Map the "Save Quick State" and "Load Quick State" hotkeys
+to your controller,
+and you can cheese your way through just about anything.
+
 Manager states
 --------------
 
+higan's
+[State Manager](../interface/higan-tools.md#the-state-manager)
+allows you to create over a hundred save states,
+and add a helpful description to each one.
+
+Manager States are more cumbersome to use than Quick States,
+since they cannot be accessed with hotkeys,
+but are useful when you want quick access
+to many different parts of a game.