Video Memory. Part II

To increase the system’s productivity, you can place an area of the constant memory which is not engaged in video-BIOS into the “fast” operating memory.

To transfer data from the slow constant memory into the “fast” operating memory (cache operation), use the parameter “Video RAM Cacheable”. This parameter may have two values: Enabled – memory caching is enabled and Disabled – caching is disabled. To transfer data in operating memory, all memory cells are reserved at the addresses A0000h-AFFFFh.

Video system with AGP-interface enables to use operating memory for storing all necessary data, i.e. your graphic adapter can obtain access to these data and operate with them directly in the system memory. The size of allocated memory depends on sizes of operating memory and video memory and is set by the parameter “AGP Aperture Memory Size” (AGP Aperture Size, Graphics Aperture). In practice, no operating memory is reserved, for example, during data caching. In fact, only an address space is allocated. In case of necessity, the video processor may request this address space only when its own memory is not enough. Thus, the larger your video memory is, the fewer apertures you will need.

As a rule, the parameter “AGP Aperture Memory Size” uses a set of real values: 8 MB, 16 MB, 32 MB, 64 MB, 128 MB or 256 MB. This set is individual for each type of BIOS. In general, you can select two values: 32 MB or 64 MB.

To speed up your memory operation, you can switch on the prefetch mode by the parameter “AGP to DRAM Prefetch”. This parameter has got two values: Enabled or Disabled. If this mode is on, the next data will be automatically read before finishing reading of the previous data. This process significantly increases the operating speed.