or Extended System Configuration Data
is a part of nonvolatile BIOS memory
(aka CMOS memory) on the motherboard
of a personal computer
, where information about ISA PnP
devices is stored. It's used by the BIOS
to allocate resources for devices
like expansion cards
The BIOS also updates the ESCD each time the hardware configuration changes, after deciding how to re-allocate resources like IRQ and memory 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.
An ISA Configuration Utility (ICU) can be used to update the ESCD via PnP BIOS interfaces. The Microsoft Windows operating system Device Manager is an instance of such a utility (and more).