PnP or how PCI works , called plug and play (PnP).                                 See related page Drivers. 
By: Deadpool.  (see how to sniff out devices with a sniffer tool !)
PnP is complex and the cures can be hard to impossible, the below covers them all. (learn that if there is a driver at all, we will find it)
First the easy way , pure magic, (the PC is Toaster way) I plug in the Ethernet cable from my  router/modem to PC jack and connect AC power, and boot my PC and PnP works like magic, if not see below reasons.

Plug and Play (PnP is a process that both Window and newer LINUX both do , to detect, and discover what chips  are in your PC and to find a correct matching driver to your OS (OS,means your operating system, and should never be XP)
PnP begins at the BIOS execution level (cold boot) and BIOS scans the PC for all hardware resources, that are available,  memory size, and I/O port devices and interrupt allocations , addin cards, etc and passes this resource data to the OS, maturing at Windows 2000 and beyond.
Linux started much later or not at all (100s of distributions of Linux, I will  not attempt to cover that, just Windows)
PnP fails for 3 reasons , the local driver cache has no driver ,or the PC is not internet connected now, or there is no driver at all for THIS OS. (read none ever made by any human on earth)

Here is a crude and  is a serial  simple PnP flow chart:

  • BIOS scans some devices (not all and not USB option devices, but yes, USB chips are discovered here but sometimes not the USB3 chips.... oops...) My lap top finds USB2 and its internal camera. (if not the CAM is born dead)
  • BIOS then passes these facts to the OS next (via a shared memory location)
  • The OS boots and then runs a deep PCI PnP scans, it scans for many things, and misses nothing, SEE the on this.  See how enumeration scans work !!! at WIKI? This does repeat if you plug in a new USB device.
  • This scan searches deep, then repeats if you add or remove any USB devices. 
  • Then with the 2 codes (and version codes) VEN and DEV,  are seen it is recorded and is used next by the OS. VEN means Vendor or Manufactures name, like code 8086 =
  • THE OS then looks in the local OS driver cash to match those 2 codes above to a matching OS specific Device driver in the driver store. (if running XP service pack 3, SP3, more drivers are there now, added)
  • If the local driver is not found (no match) the OS finds a open internet connection, via wifi or LAN  ports.   (if not connected now, all hope is lost , halt here and see last line below)
  • If you have W10 it can find drivers on you subnet other PCs at home or a business, if that feature was  turned ON by you , or finds them on your neighbors PC, again if turned on by them, . If fail  we go to the next step/
  • If not found yet the OS goes to  MS driver servers, and  catalogs, (if XP or VISTA you just failed here, they are now gone and off line , only service packs remain for  XP)
  • If  the OS found the driver , matching the 2 codes,  then the OS is happy and they will work, if not see next line statement.
  • The OS marks the DEVICES (in device manager) as RED, YELLOW or UNKNOWN, Thus ends PnP until say you plug in a new device, or reboot with something new.
  • Learn that Unknown, still has 2 codes of you were to look,  Unknown means "NO MATCH-UP"

PnP fails for only 2 reasons. (I will  assume your PC is not infected and the OS is freshly loaded)
  1. The driver is not found local driver cache (in C: windows folders)
  2. The driver does not exist for any reason in the Microsoft Driver server catalogs, online (or your not online?) Be ONLINE! or the makers of chip are long out of business or no longer support this chip for any reason whatsoever.
If not online?, read this.

This next section  below shows how to scan and detect hardware, just like BIOS PnP does. (call PCI scans) BIOS PnP evolved fast after 1994 this Intel document.
When XP was killed dead by Microsoft, or Vista then Plug and play died, (it does now!)  the tech.  He scans it by hand running the sniffer .
If a device driver is missing XP can only find it in your local driver cache,  C:/windows/drivers,etc  if not it goes online to MS.COM but  this path is now dead at MS.
Now Vista is dead in this way.

Next up is?  PCI, it's a standard for asking chips who they are. (chip info scans)
PnP also finds printers, scanners, Displays, keyboards, mice , and a zillion and one , USB devices. (PnP job is to find all devices that need to work here)

Next is called hand scanning... for chips,
TITLE: HOW to SNIFF CHIPS , so you can match up drives (101)
Rule 1 on scans, if say your USB2 port is dead, the internal camera will be both dead and invisible to scans ( like trying to see in to a room and can't but the door is locked, USB door, if you get my drift)

 First may I say if you can't use Ethernet (you own what I call potato chip thin notebooks,  (I hate them) then get wifi working first, or PnP will be 1/2 dead or worse.
There is cure for above, pain, a Ethernet (LAN) USB dongle, buy one for those days, WIFI is hopeless. (as can be)

Well, I run this  program called PCI scan,  that finds all chips in any PC.( the newest version is even better, and finds my wifi chip fast)
I use PCIsniffer v3, by Milray, direct. (< link busted )Please us this  link instead at Major GEEKs.

One Example only (there are 20million drivers now, and most are DEAD!)
In this case, my WIFI chip was dead and Device Manager (DM) showed it missing, (or unknown or marked RED or YELLOW) In some cases using a MS install disk (bad) on a HP PC, you can see 10 things in DM , as Unknown, like the fingerprint reader.
I fiddle about in this Sniffer engine, and find my chip, easy as apple pie. (Ethernet first then wifi last)
In DM you see this.,  See details,  even a dead chip has this, even UNKNOWN (unknown only means I can not find a match , the OS can't but you can) dig?  Click details, read the numbers write them down, now.
See VEN,  Ven means vendor,  or maker, can by INTEL or RealTek and many others, thing of VEN as  house address and then DEV as ROOM in that house.  DEV is for Device, that they made , in this case Network chip.

If for some reason VEN and DEV can't be found. (try to know fixing one, bad driver, will unmask more chips (some are cascaded is why)
PCISniffer 3:
(love it I do) I have it on boot mini CD and on STICK USB.

My INTEL Ethernet card  is on the left B0 but B68 (say buss 68)  Is my WIFI chip and is an  Intel (8086) chip and is code 4239h, if I use the database scan , you look it up that way.

To use this program, boot to CD  (or stick) open all left sides items so you see all B0:xxxxxxxxx items, the click each and see what it is at the top of the screen , in this case the  Centrino N6200 wifi chip, click Ethernet on left side, to see it.

The sniffer can even find this card,. Windows 95 PCI card that works.
After you find what chip is dead, (even Device manager told you it was dead) but you found it using the SNIFFER,  then see my DRIVERS page next.
Once we get this far with a makers name and Device name,
We then go to HP and get it or from the actual maker LAST,  (If  video GPU chip go to Nvidia or AMD/ATI home page for drivers and get now)
If not video, go to HP and get your driver there, first. or if not supported at HP then at the chip makers site, if still in business. (google" Realtek home") or Intel home, or Intel drivers. like that, easy no? but not if they left this business.

The REALITIES OF Progress or failures, yes companies die and even products die. (and kills PnP dead)
A more simple list of PnP FAILURES.  (example WIFI chips) A key chip, for sure.  (Both Microsoft and HP are helpless to support you with DEAD CHIPs)  (dead means zero maker support now, for many reasons.)  (maker means chip maker or CARD PCI? maker)
There are 20 million drivers, and chips and devices , printers scanners ,video cards, vast numbers of different addin cards and USB devices, (millions) most are now Obsolete ( if you look at the last 10 years only devices, most devices before it are obsolete back to 1981.)
When I say chip this can be literally the chip or device that is bundle of chips doing a specific task (like Printer or scanners do)
  • The chip maker went out of business in say 1985 or year 1999-2000 (vast have since, then to now)   (or merged and died, hostile take overs, are real)  Ever heard of Diamond Multimedia or S3?(gone !)
  • The maker is still in business, but only makes Toasters now. (or lamp shades? or window shades? )
  • The Maker no longer makes wifi chips, now (or this DEVICE that fails to work)
  • The Maker makes wifi chips still, but  not that model  now, they make newer owns, like what Intel does.  (see Intel's list of non supported products,or listed as END OF LIFE)
  • The maker never made a W10 driver  nor ever will. (there are millions of chip like this, now DEAD) One way to think of Windows 10 is it works on PC 10 years or newer, and never with a 20 year old 3com card. 
  • The maker stopped support at Windows  VISTA for drivers, for this chip. (or stopped at XP or at W7)
  • Last and most complex, the chips called Glue logic chips that connect up to your (eg.) wifi chip, and is no longer made or supported, Like old Nvidia, Nforce chips.  (they need to play together too... all chips as at team) os now dead with newer windows.
  •  Some PCs use FPGA chips that need it working first or the others  connected to it can fail. (there are vast kinds of Glue logic, some use a huge  DSP, chip or other complex devices to form the full PC architectural structure of a PC.)  a hopeless place to be...
  • Some PC, the USB 2 chip must work first of the internal camera will be dead, (HP 8540 is one)
Find video drivers can be easy at AMD/ATI or at NVidia if the video is messed up, a super easy fix.
Here is the Nvidia trick , in this page, set the first toggle box line to LEGACY and see all drivers for all OS there, on nFORCE (they hid it deep with this trick)
  Do know that W7 was the last OS supported for most of these, old Nforce chips. But might work ! Try it, see for  your self, what works.
Case in point, if the Ethernet chip driver is missing, here it be.!
If you need old Intel drivers, go to home. and get them.
That ends the why, now the cure.  (the above complexity is why PnP exists in the first place)

 Google how many video cards makers no longer exist.  (endless story 2  here) 
Hint: don't expect Microsoft to support dead chips, when the DRIVERS DO NOT EXIST any where on mother earth. (for this OS)
Do not expect HP to have drivers for chips not made or never ever had a driver for W7, W8 or W10 .

The top chip makers are here today.

Use the database table look up's next , after you  scan, your PC and learn VEN/DEV codes seen below.  (A good place to see links to PC ID repositories is here)

PnP, PCI master data base look up's (off line now?):        This is Alternate #1

The fastest cure, after PnP failures is to let PnP find it on the internet, "BE CONNECTED"
The site has all my drivers,  I then load them all and now it works great. (in the correct order , I do that) Older that 10 years, last model made , HP support ends.
Lets say you are trying to buck the system and run a newer OS on your old PC, that does not support, well you get to do all this the the long hard way... (It was your choice, bucking the HP system of full support, Why do that ?, I DO but I know how to...)

CURE 1:  (HP no help, Microsoft no help and you are H3LL bent to find a driver that works)
The easy way.:
Use your OS, in this case WINDOW 10.  I use device manager to find the identity of the dead chip. (click start, click control panel, click device manager.)
The hard way:
Example of 1 NIC card chip (PCI)   (a.k.a: Ethernet chip) A very key chip that must work now, so PnP can get working drivers off the internet, so we make this work FIRST and its cable (by all means possible !)
We are here because this chip is dead or PnP fails for this chip now.
This is the best way to look up chips and match drivers. DEV = device code and VEN = Vendor,(makers name code) In this case Realtek.
If you see RED or Yellow or UNKNOWN, error  mark's here, that means the drivers are wrong. (missing or corrupted by a Virus) HP may have  the correct drivers, . (go there and get them, if PnP fails)  Here are mine, as 1 small example.
The Device manager  sees all chip devices and may  show errors.  (in some cases it shows UNKNOWN devices, and has no codes for it , in that case see section CURE 2 below.
These are what the PnP scan codes see at boot up, VEN is maker, DEV is chip name coded, we can find these easy , via data bases covering them.
all you need is the blue highlighted line of data. Realtek  Dev 8168 means RTL8168E / RTL8111F

I see those 2 codes, VEN and DEV and look them up in the PCI master data base above.  (VEN means vendor or chip maker code, 8086 is intel,  DEV means Device, or CHIP code)
I now know the makers real name and chip real part number. (armed with this key fact , I might ! find a driver, that works)
This allows me go to RealTek (code 8168)  home page (they are this chip maker ) and see every driver ever  made for all operating systems, supported by them.
Lets say this chip ended at Windows 7, but I try it on Windows 10 and it works (luck does happen). (if not, you should not have upgraded to W10, as HP did advise you..
One trick is use a Vista or newer driver and install in using MS compatibility mode, (right click the driver installer and pick that method, say its VISTA code, so use VISTA incompatibly mode) It can work, but may work and be limited it scope and features)
What if your WIFI is dead,  what good is this PC to you now, from some its now useless. (or try the wired Ethernet jack to your router up first then get wifi up 2nd.)

Tricks:  Use the most newest driver you can find and pry. Plug and Pray.
Do not expect XP drivers to work on newer OS. (for sure GPU will fail !)
Use VISTA or newer driver in all cases.
Trick 2, is use the driver installer, EXE  you found and right click install it under compatible mode.  (say its W7 and only VISTA has a driver, so pick Vista Compatible load and run)
end easy way.

USB PnP, issues:
There are near Infinite USB devices now (plug-in),  Millions ! of drivers (over 16 years worth of them and many are not supported today, like a 2001 Web cam?)
Know that some PC's have 2 USB chips, 1 for USB3, and one for the older USB ports. 1 might work and the the other not until you load its driver first.
That PC has 2 chips, and if the driver for USB3 is missing it will be dead. (port dead)
The Device manager must be clear of all errors related to a dead port USB first.
Then when that works correctly (ports) there is a chance the USB device you just plugged in can work  (be connected to the internet or fail 1/2 the time)
Know too that some mice and keyboards use Bluetooth wireless technology, and  both devices must have a good battery inside the device (mouse) to use Bluetooth (BT), and the drivers must be good too.
If say a BT mouse fails, then  try a wired mouse in the same USB port, see it works now doesn't it. (tells you that bluetooth mouse is belly up , right?)
When you plug in any USB device to any port, the PC will go dingdong, this tells that the OS saw the device, connection,  and if the driver is missing it now attempts to get a good one, via internet, in most cases. (It wants fresh drivers, that work is why)
Windows XP must have SP3 installed, Service PACK 3. or USB support will be HORRID, even with SP3, many devices will NOT BE SUPPORTED,  get rid of XP now.  (contact your maker of said device and ask them for XP support,  and get laughs....)
The driver can be found if lucky as seen here.

What does Support mean (HP example)
  1. The Warranty will be honored.
  2. 10 years of free OS and driver support at  from the last model made not first.   Find my drivers, (must match full p/n # and your serial number,  the SERVICE TAG , DAT:
  3. Direct help with problems with your HP , PC.
  4. Support for  all  OS installed day one (some PC have 3 choices) not counting 32 or 64bit OS. (creating 6 choices new)
  5. 10 years of media kit support, at  (CD/DVC install disk, or USB media memory stick support.  (there is a small charge for these kits)   HP get media install kit for your PC.(must match your PC )
  6. Help on the HP forum for problems (regardless of PCs age) HP Forum , ask for help there,  log in and ask any one can.
  7. The HP Driver page may have a driver autoloader program called SOFTPAQ,  if present , it then ID's your PC and loads the correct drivers, and apps.,, if you leave HP support , this magic ends, now.
  8. If you leave HP support , you lose the HP applications too. (including the Security package software and more)  There is one driver for the laptop upper row buttons, that MS my not support directly , only HP.  (eg: volume, wifi on/off, etc)
  9. HP nor MS support XP nor VISTA now. SORRY !
If you abandon the above,  and use MICROSOFT install disk (ISO or STICK) installed OS, then HP support ends.
I'm running W10 on my PC's now, with zero HP support, but I had to force feed many missing drivers. (using the PnP PCI scanner then going to the true chip maker drivers, and getting all w10 working drivers from them, a long and tedious process)
In most cases, just boot and hit F10, XP or F11 for Vista on up, and restore the OS with Drivers , fresh, in one fell swoop.  F11 is the hot key at power on that reloads the OS back to factory fresh day.  The HP OS recovery key started around 2006.

I did PnP tests on XP +SP3 ,  to see if the Microsoft Update servers still serving up the are fully but not drivers,  DRIVERS, seen here. (I see are about 1/2 up,  and MS told me it is going DEAD SOON !
The cure is the XP  Monster CD. 

less is more.... I'm still editing this text.

ver.3 :::::::4-15-2017