MSI 845 PRO4 Manual page 59

Chapter 3
AGP Aperture Size (MB)
This item allows you to select the size of the Accelerated Graphics Port
(AGP) aperture. Aperture is a portion of the PCI memory address range
dedicated for graphics memory address space. Host cycles that hit the
aperture range are forwarded to the AGP without any translation. Avail-
able options are [4], [8], [16], [32], [64], [128], and [256]. Default value is
[64].
3-16