Plug and Play BIOS Specification

Plug and Play BIOS Specification 1.0A Page 46
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A BIOS implementor is only required to follow the interface described by this function. The format of the
data passed by the system software must follow the Plug and Play ISA resource descriptor definition. How
the statically allocated resource information is actually stored is left up to the BIOS implementor. An
example of how the information could be stored more compactly than the Plug and Play ISA resource
descriptors is as follows:
IRQ 2 Bytes - Bits set indicate IRQ used by unconfigurable ISA device
DMA 1 Byte - Bits set indicate DMA used by unconfigurable ISA device
I/O 24 Bytes - Bits set indicate I/O addresses used (100h-3ffh). Assumes 4 ports used per
I/O address bit set
Memory 640k to 1Mg 3 Bytes - Represented in 16k blocks
Memory 1Mg to 16Mg 2 Bytes - Represented in 1Mg increments.
Storing the information this way would allow the system resources used by unconfigurable ISA devices to
be contained in 32 bytes.
Note: this is only an example. It is completely up to the BIOS vendor to choose an appropriate format
for storing the data, which means it could possibly be stored in less than 32 bytes or require more than
32 bytes.