Shadow Memory. Part III

It is also recommended to shadow memory for video-BIOS when you play the DOS-games or call the DOS-programs from more “advanced” operating systems (Windows95 and higher). In this case, your program (or game) directly requests to video-BIOS, bypassing the functional capacities of the current operating system. If the DOS-programs are not used, it is better to switch off the parameter of video-BIOS shadowing.

Except the parameter that offers to shadow the entire memory area, some versions of BIOS use the parameters that enable to shadow some parts of memory. These parameters are completely identical to the parameters described above, for example: Video ROM Shadow C000, 16K and Video ROM Shadow C400, 16K.

To shadow memory for the devices connected to ISA-bus, you may use the parameter “Memory Hole At 15M-16M” (Memory Hole). Using this parameter, an area between 15 and 16 MB, to which the constant memory of the appropriate ISA-devices is shifted, is transferred to operating memory. This parameter may have two values: Enabled and Disabled. This parameter enables to increase the productivity of appropriate input/output devices but locks an access to an appropriate address space for other programs. If this parameter is on, your operating memory actually losses one GB of its volume, so if you do not use ISA-devices or their productivity is not important for you, this parameter should be turned off.

The parameters described above may also have the following values: None – shadowing is prohibited; at 512 kB (512 KB-640 KB, Conventional) – memory shadowing between 512 and 640 KB; at 15 MB (15MB-16MB, Extended) – memory shadowing between 15 and 16 MB.