Although Windows '95 or a PnP BIOS can do a lot by themselves, you really need the lot, e.g. a Plug and Play BIOS, with compatible devices and an Operating System for the best performance. Operating Systems that natively support PnP are Windows 95/98, 2000 and OS/2. Linux can also handle it with its own software, as can Windows NT with a module on the installation CD, but it's not supported by Microsoft. Note that these systems do not require PnP hardware - devices won't be configured without the right system, but you just have to do it manually, like with non-PnP stuff. 

Be aware that not all PCI (2.0) cards are PnP, and that although PC (PCMCIA) cards are "Plug and Play", they are not considered here. Also, anything using PCI address ranges will not be seen by the BIOS on boot-up, which doesn't mean that it isn't working. 

PnP itself was originally devised by Compaq, Intel and Phoenix. Your chipset settings may allow you to choose of two methods of operation (with the Plug and Play OS setting): 

• All PnP devices are configured and activated. 

• All PnP ISA cards are isolated and checked, but only those needed to boot the machine are activated.

The ISA system cannot produce specific information about a card, so the BIOS has to isolate each one and give it a temporary handle so its requirements can be read. Resources can be allocated once all cards have been dealt with (recommended for Windows '95, as it can use the Registry and its own procedures to use the same information every time you boot). 

This leads to.... 

ESCD (Extended System Configuration Data), a system which is part of PnP (actually a superset of EISA), that can store data on PnP or non-PnP EISA, ISA or PCI cards to perform the same function as the Windows '95 Registry above, that is, provide consistency between sessions by reserving specific configurations for individual cards. Without ESCD, each boot sequence is a new adventure for the system. It occupies part of Upper Memory (E000-EDFF), which is not available to memory managers. The default length is 4K, and problems have been reported with EMS buffer addressing when this area has been used.

This is an article from  Phil Croucher, author of  Communications and Networks.  Phil has a way of explaining in "plain" English. The information is well presented and is well above A+ standard.