Source 2006

The engine branch, also known as the Episode One engine branch, and the last Old Engine branch, was first used in 2005 with and (with updated to run on this branch), but was not properly released until 2006 with , with previous multiplayer games (, , and ) also being upgraded to the branch then. It was distributed in "base source engine 2.gcf." It was succeeded by (also known as Orange Box) branch, but still receiving engine updates until December 2009. It requires content to operate.
The engine versions for this branch are (Lost Coast) or (EP1) up to ().
The SDK and SDK Base game for this branch are free to all Steam users.
== Features ==
New since :
; High Dynamic Range rendering 
: A simulation of brightness values outside computer monitors' actual range, and of aperture adjustment.
:
; Film grain post-processing effect
: Used in .
; Color correction
: Alter the color balance of an image to achieve a desired effect. For example, in , the color has been adjusted to be more desaturated.
; Phong materials
: Diffuse reflections for skin and other roughened surfaces on models.
; Facial animation upgrades
: More detail and intenser shapes for close-up performances.
; Commentary System
: Allows DVD-like director's commentary to be embedded inside levels. 
; Dynamic interactions
: Dynamic interactions between NPCs using special animations.
; Lightwarp textures 
: 1D textures that tint a material per-texel depending on their brightness.
; Direct3D 9 - Shader Model 3 (DirectX 9.0+ feature level/)
: Unlocks greatly improved shader performance.
; Detail prop shapes
: Improved detail sprites that sway in the breeze and bend away from nearby players.
; BSP version 20
: New BSP version, with new lumps.
: Patching levels with lump files - update entity lumps, changing a .BSP file's entities without recompiling the maps.
== Removed features ==
; DirectX 6.0 () compatibility level
: Support for DirectX 6.x GPUs has been partially dropped, but still usable.
; Steam Friends & Parlor Games menu
: Originally present before it was eventually removed in favor of Steam Overlay which is introduced in 2009. Servers for Steam Friends feature was also shut down.
; 64-bit support
: Originally, (runs on early version of ) had a 64-bit version of the engine, allowing it to access more than 2GB (4GB with LAA) of RAM, and increase performance slightly. However it was later discontinued and removed due to it's instability on some systems.
== Availability ==
Gamecode for the 2006 branch is included in the now-deprecated Source SDK app. All Valve games introduced with and previous titles that are upgraded from to are now currently using or . To compile the code for 2006 branch, see Compiling under VS2005.
== Usage ==
The following games still run on :
=== Valve ===
* 
=== Third-Party ===
* and 
* 
* 
* 
* 
* Iron Grip: The Oppression
* 
* 
** Heavily modified, and uses proprietary file format to store game files. Also support Direct3D (DirectX) 11.
== Known issues ==
== System Requirements ==
Minimum Specs :
*OS: Windows 98 / ME, 2000, XP or later
*CPU: 1.2 GHz 
*RAM: 256 MB 
*Nvidia GeForce FX 5700, ATI Radeon 9500 (with 128MB VRAM)
*Direct3D 9.0 compatible video card (with atleast DirectX 7.0 compatibility level or higher)
Category:Official Engine Branches