When performing a "Configuration Space" access, a PCI device does not decode the address to determine if it should respond, but instead looks at the "Initialization Device Select" signal (IDSEL). There is a system-wide unique activation method for each IDSEL signal. The PCI device is required to decode only the lowest order 11 bits of the address space (ADto AD[0) address/data signals, and can ignore decoding the 21 high order A/D signals (ADto AD[11) because a "Configuration Space" access implementation has each slot's IDSEL pin connected to a different high order address/data line ADthrough AD[31. The IDSEL signal is a different pin for each PCI device/adapter slot.