Copied from: http://lwn.net/Articles/143397/
Starting with kernel 2.6 there's a new /sys directory for PnP configuration. It's a sysfs type of file system and it's something like the /proc filesystem since the "files" represent information in the kernel memory and are not on your harddrive. But it's not as useful as the /proc filesystem. Originally (in the 2.5 kernels) it was called "driver file system" of type "driverfs".
In the sysfs, each device which exists on your system has it's own directory which contains files showing the resources allocated to it. Such device directories have names like 0000:00:12.0@ or 00:06@. What devices are these? The first is a PCI card in "slot" 12 of your PC. The slot may actually be labeled PCI2 inside your PC (2 instead of 12). That's because low numbered "slots" are used for built-in devices on the motherboard that don't use any physical slots. In this example, "slots" 1-10 would be built-in and actual slots 11-14 are labeled 1-4. By typing "lspci" you'll be able to match the numbers (like 0000:00:12.0) to names (like IDE interface). Type "lspci -v" or "lspci -vv" to see more.
Well then, what is 00:06 ? It's an ISA card (or built-in device) but it's not ISA slot 6 (like the PCI numbering). When a search was made for ISA-PNP devices, it was the 6th one found. More precisely, it was the 7th one found since there's a device numbered: 00:00. So how does one identify them? Well, you could type: "cat */*" and display all the files for all the devices, but even then you don't see the device names (but do see info from which you can identify them). This inconvenience will hopefully be fixed in the future.
Not only do these files supply information on the bus-resource configuration (in somewhat cryptic format) and drivers (in "driver" directories), but in the future, you should be able to use them to change the resource configuration. Right now (Aug 2004) you can't configure the PCI bus with it. A serious limitation is that per the present "driver model" you can't change the resource of a device that has been assigned to a driver which likely means that you'll need to unload the driver module in order to use it. If the driver is built in, there's no hope. These serious limitations will hopefully be eliminated in the future. In the kernel documentation is a file: "pnp.txt" telling how to configure. As of Aug. 2004, it was much out-of-date but the author is working on an update. Using the /sys tree to configure resources is known as the "Linux Plug and Play User Interface".The other part of "Linux Plug and Play" is the kernel interface used by device drivers. This has changed a lot starting with kernel 2.6 but most drivers are still using the old interface (as of Aug. 2004). It's possible also for drivers (or you) to use the "user interface" which needs improvement