TheExtended System Configuration Data (ESCD) is a specification for configuringx86 computers of theISA PNP era. The specification was developed byCompaq,Intel andPhoenix Technologies. It consists of a method for storing configuration information innonvolatile BIOS memory and threeBIOS functions for working with that data.[1][2]
The ESCD data may at one time have been stored in the latter portion of the 128 byte extended bank of battery-backed CMOS RAM but eventually it became too large and so was moved to BIOS flash.[3][4]
It contains information aboutISAPnP devices is stored. It is used by theBIOS to allocate resources fordevices likeexpansion cards. The ESCD data is stored using the data serialization format used forEISA. Its data starts with the "ACFG" signature in ASCII. PCI configuration can also be stored in ESCD, using virtual slots.[5] Typical storage usage for ESCD data is 2–4 KB
The BIOS also updates the ESCD each time thehardware configuration changes, after deciding how to re-allocate resources likeIRQ andmemory mapping ranges. After the ESCD has been updated, the decision need not be made again, which thereafter results in faster startup without conflicts until the next hardware configuration change.
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