A PnP BIOS keeps a record of resources in use through a Non-Volatile
   RAM (NVRAM), usually part of its Flash BIOS EEPROM. When you add a
   device, Win95 tells the BIOS to add the resources in use to this list.
   A BIOS must have these calls available to Win95 or it will never know
   about what the OS added or reserved. The NVRAM is not the same as CMOS
   RAM, which makes me wonder why they don't just replace the CMOS with
   NVRAM for storing other settings, like lost hard drive parameters.
   
   Also, when you install a PnP device, the BIOS polls it for the
   resources it requires. The PnP device will have "Preferred",
   "Acceptable", and "Marginal" operating resource requirements. The BIOS
   will assign resources based on what the device can use, and record the
   resources used in its NVRAM. Win95 can ask the BIOS what resources are
   in use, and it can ask the BIOS if any new devices exist, which is
   when you get the "Windows has found new hardware..." message. On a
   Non-PnP system, Win95 handles all PnP requests by itself and stores
   config info in the Registry.
   
   Buggy BIOSes might not handle cards with multiple devices on it. If
   you think you have a buggy BIOS, see about disabling its PnP features
   and let Win95 take over as PnP manager. In this condition, Win95
   stores all resources in use in its Registry and polls PnP cards by
   itself.
   

Some parts © 2009 Advameg, Inc.