From
http://support.apple.com/kb/ht3246:
GMA X3100
The GMA X3100 allocates a base amount of 144 MB for video and boot processes at startup. For example, a MacBook (Late 2007) with 1 GB of RAM installed has 880 MB of memory available to Mac OS X and applications (1024-144=880).
Products with the Intel GMA X3100 include:
* MacBook (Late 2007)
* MacBook (Early 2008)
* MacBook (Late 2008)
* MacBook Air (Early 2008)
Note: Depending on the application or task being accomplished, Mac OS X may make additional main memory available to the graphics processor for texture use beyond the base amount mentioned above. The most common types of applications that request more system memory to be used as graphics memory are 3D and graphics-intense applications. Using an extended desktop or mirrored desktop may also increase the amount of system memory used as graphics memory. For example, the GMA 950 would allocate 80 MB, resulting in 432 MB of available memory (512-80=432). Likewise, the GMA X3100 would allocate 160 MB, resulting in 864 MB of available memory (1024-160=864).
