|
This BIOS feature allows you to select the size of the AGP aperture. The aperture is a portion of the PCI memory address range that is to be dedicated for use as AGP memory address space. Host cycles that hit the aperture range are forwarded to the AGP bus without need for translation. The aperture size also determines the maximum amount of system RAM that can be allocated to the AGP graphics card for texture storage.
The AGP aperture size should be calculated using this formula : maximum usable AGP memory size x 2 plus 12MB. The actual usable AGP memory space is less than half the AGP aperture size set in the BIOS. This is because the AGP controller needs a write combined memory area equal in size to the actual AGP memory area (uncached) plus an additional 12MB for virtual addressing. Therefore, it isn't simply a matter of determining how much AGP memory space you need. You also need to calculate the final aperture size by doubling the amount of AGP memory space desired and adding 12MB to the total.
Note that the AGP aperture is merely address space, not physical memory in use. The physical memory is allocated and released as needed only when Direct3D makes a "create non-local surface" call. Windows 95 (with VGARTD.VXD) and later versions of Microsoft Windows use a waterfall method of memory allocation. Surfaces are first created in the graphics card's local memory. When that memory is full, surface creation spills over into AGP memory and then system memory. So, memory usage is automatically optimized for each application. AGP and system memory are not used unless absolutely necessary.
----
The AGP aperture is often referred to as non-local-video address space since this space is being used by the graphics devices. During the PCI enumeration, the Host-To-PCI bridge device assigns device (graphics card) address space. The size of the address space ranges from 4MB to 256MB and is configured in the BIOS and will most likely default to 64MB. In some cases, the system BIOS will allow the user to change it. Intel recommends that the aperture always be set at 64MB even if the amount of actual system memory (RAM) is less than 64MB.
----
It is quite common to hear many people recommending that the AGP aperture size should be exactly half the amount of system RAM. However, this is wrong for the same reason why swapfile size shouldn't always be 1/4 of system RAM. Like the swapfile, the requirement for AGP memory space shrinks as the graphics card's local memory increases in size. This is because the graphics card will have more local memory to dedicate to texture storage. This reduces the need for AGP memory. So, if you upgrade to a graphics card with more memory, you shouldn't be "deceived" into thinking that it will therefore require even more AGP memory! On the contrary, a smaller AGP memory space will be required.
----
Kannattaa lukee toi jos on epävarma siitä mitä tuo AGP aperture size tarkottaa.
Viestiä on muokattu lähettämisen jälkeen. Viimeisin muokkaus 17. joulukuuta 2005 @ 21:13
|
