## Virtual Device Driver Reference for OS/2

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### Adapter ROM

At system initialization, the virtual BIOS device driver searches the region between the top of the DOS user space (RMSIZE) and 1MB to find all of the adapter ROM. Adapter ROMs that include the ROM signature will be found. In a normal DOS session creation (without any Include/Exclude properties specified), these linear addresses are mapped to corresponding physical ROM.

All the ranges specified in the DOS setting MEM_INCLUDE_REGIONS are taken out of the list used for mapping the linear addresses to corresponding physical ROM. As a result, MEM_INCLUDE_REGIONS is not mapped to physical ROM and it remains available to EMM or XMS.

For MEM_EXCLUDE_REGIONS, the virtual BIOS device driver reserves those regions and maps them to their corresponding physical addresses. This allows the user the ability to map adapter ROM that does not contain the ROM signature and adapter RAM.