Biome/Before Beta 1.8

Biomes were updated in Alpha 1.2.0, also known as the Halloween Update.

Prior to the Halloween Update, a map had either a Snowy or Grassy theme that the player could choose between when creating the world. After the update, a world includes all biome themes generated in a distribution range that is determined from the biomes graph.

There were 13 biome types in 1.7: 10 in the Overworld, 1 in the Nether, and 2 unused ones that are in the code but aren't encountered in normal play.

Pre-Update Saves
Worlds generated prior to the update remained unchanged except for changes in grass color. This "biome" is known as Shrubland. However, any new chunks generated (by the player moving outside of the pre-biome world's generated bounds) do generate biomes, similar to the Nether being generated when you first enter it from a portal. Moving from 1.7.3 or earlier to 1.8 or later, the previous generated terrain stays the same but is in a different 1.8 biome. This is shown by the grass and leaf colors. A 1.7.3 forest biome could have the grass and leaf colors of a desert biome.

Taiga and Tundra biomes in 1.8
In 1.8, Notch said the Taiga and Tundra biomes would be left out until 1.9 because of problems in the biome generation code, but it only concerns the snow weather and snow layers as the other common features of this type of land can still be generated.