Explanation of Xorg.conf Extension Modules

1. dbe:
Required for animations. Implements Double buffering for flicker free and smooth of animations.

2. extmod:
Loads module for performing common functions in X Server.

3. fbdevhw:
The Linux framebuffer module which is used to let x communicate with framebuffer device in linux.(/dev/fb0)

4. glx:
The glx extension connects the DRI 3D library and X.
the following command gives you information about glx and the fps at which xserver functions:-

5. record:
The record module adds record extension to capture events that are associated with recording and playback user actions.

6. dri:
Loads Direct Rendering Interface to provide accelerated 3d graphics. NOT SUPPORTED BY NVIDIA CARDS

7. freetype:
Loads the module that can handle TrueType (.ttf and .ttc) ,Type1 (.pfa and .pbf) and OpenType (.otf and .otc) Fonts

8. vbe
VESA BIOS Extensions (VBE) comprise a VESA standard that defines the interface that can be used by software to access compliant video boards at high resolutions and bit depths. This is opposed to the "traditional" int 10h BIOS calls, which max out at the resolution of 640×480 pixels with 16 color (4-bit) depth.

9. composite
This extension allows for all drawing to occur on an offscreen buffer first, then it is blitted to the actual framebuffer when all drawing is done. This allows for flicker free rendering and some other cool effects (like real transparency and shadows... which are next!). Workstations overlays and Composite are mutually exclusive. If you're using a Nvidia Quadro4 XGL or Quadro FX based card, you can use either Composite or OpenGL overlays, but not both. To use overlays (and you most likely want to, as it's one of the most important features of the Quadro cards), you have to disable the Composite extension.

Additionally there can also be another section called DRI ,

Section "DRI"
Mode 0000
# Specifies the read/write permission mode in which DRI will run. Eg: 0666 means any user can read/write whileas 0660 only owner or the same group member can do so.
EndSection