Choose this option if you have a system that has "Intel Graphics
Media Accelerator" or "HD Graphics" integrated graphics,
including 830M, 845G, 852GM, 855GM, 865G, 915G, 945G, 965G,
G35, G41, G43, G45 chipsets and Celeron, Pentium, Core i3,
Core i5, Core i7 as well as Atom CPUs with integrated graphics.
If M is selected, the module will be called i915. AGP support
is required for this driver to work. This driver is used by
the Intel driver in X.org 6.8 and XFree86 4.4 and above. It
replaces the older i830 module that supported a subset of the
hardware in older X.org releases.

Note that the older i810/i815 chipsets require the use of the
i810 driver instead, and the Atom z5xx series has an entirely
different implementation.

source code:

drivers/gpu/drm//i915/