“Single User” is a boot mode, you actually tells the unix shell that the OS should load only prompt (no GUI), and the local console login is the only login available (can’t be logged on from the network). Now the question is why we need to boot in Single User mode and the answer is, sometimes the system requires an administrative actions by the administrator, such as disk checkup, partition altering, drivers uninstalling, backups, etc.at this delicate tasks you don’t want other users to touch/create/remove/use files, hardware, CPU, and use resources. this is why you enter into single user mode.

What can you do in “Single User” Mode?

since single user mode is for administrator and no GUI is available then every task you can do from terminal (command line) as root user you can do here, which is practically everything (on the current system) it wasn’t meant to be used for regular work such as surfing the web (there is no network) or reading files etc. you can use all the unix commands available for OS X and all the command line utilities and applications available on that machine.

How to enter Single User Mode :

1. Restart your Mac or Hackintosh.
2. Continuously press F8 until you see the Darwin boot prompt
3. Type “-s” without the quotation marks and press enter.
4. You will soon reach a command prompt
5. Note the lines written to the console about fsck and mount
6. Type : /sbin/fsck -fy
7. Type : /sbin/mount – uw / this will mount your file system
8. thats it now you are in “Single User Mode”

In single-user mode, not all functions of Mac OS X are available. To use the Mac OS X interface or other high-level aspects of Mac OS X, you need to start up in the standard mode.To switch back to the Mac OS X interface, type reboot and press the Return key. The computer restarts and you see the login dialog or the Mac desktop, depending on your login preferences.

Still waiting for root device error occured because the appropriate Sata/Pata driver isn’t being loaded. This error usually appears  before OSX86 DVD can boot and in some cases it occurs after installation. Actually this error means that the OS is set to boot from a drive and partition that does not exist or your bootloader is not able to discover the partition. Lets get started to troubleshoot the problem in the first phase we discuss the “Still Waiting For Root Device Error” which appears while installing the OSX86 on your computer.

Step 1 Jumper Settings : If your system contains IDE hard disk or DVD RW then you need to play with your jumper settings. If the following settings are not working for you try vice versa. if you have Sata Hard Disk and DVD RW skip to step 2.

• Your rom/writer must be set as Primary Master.
• Your hard-disk must be set as Primary Slave .

Step 2 Tweaking the BIOS : If you satisfies step 1 then time is to play with BIOS settings. Open your BIOS settings by pressing DEL or F2 key continuosly as you starts your PC. Once the BIOS screen appears try to find and change following options if they are available.

Step 3 Download Another Distribution : This is the most effective there are many OSX86 distro in the wild but you have to choose select one for your hardware configuration. For selecting the right one search on Wiki.OSX86project.org and forum.insanelymac.com if you find anyone who posted a success message with his details then you are lucky otherwise download the various flavours and try them.

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Still Waiting For Root Device Error After Installing The OSX86

iClairified Guide :

1. Boot up using the LeoV3 DVD as if you are going to install Mac OS X again.
2. Select Terminal from the Installer’s Utility Menu.
3. Now we are going to copy all the the ATA kexts from the install DVD to your hard drive. To do this enter a command like this:

cp -pr /Volumes/Leo4allv3/System/Library/Extensions/*ATA* /Volumes/MacHD/System/Library/Extensions/.

NOTE*: Replace Leo4allv3 with the name of your install dvd and replace MacHD with the name of your hard drive volume.

4. Now we need to set the permissions for those kexts we copied

chown -R root:wheel /Volumes/MacHD/System/Library/Extensions/*ATA*
chmod -R 755 /Volumes/MacHD/System/Library/Extensions/*ATA*

NOTE*: Replace MacHD with the name of your hard drive volume.

5. To remove the kextcache execute the following:

rm -rf /Volumes/MacHD/System/Library/Extensions.*

Note* Replace MacHD with the name of your drive volume.

You may now restart your computer. I would suggest pressing F8 while booting and then entering -f as a boot option to force reloading of the kexts.

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Apple2PC Guide :

If you know the number of your Hard Drive then at the Darwin prompt (after boot press F8) write: rd=DiskX where X is the number of your OSX hard drive.

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Tags : kalyway still waiting for root device, iatkos still waiting for root device, still waiting for root device sata, mac os still waiting for root device, still waiting for root device leopard, jas 10.4 8 still waiting for root device, still waiting for root device ide, osx still waiting for root device

Installing the OS X on your PC is difficult till first install. Successful OSX86 installation is depends on various combinations like right Distro, BIOS Settings, Hardware, Patch Selection etc. Most common problem for first time installer is my hackintosh reboots after installation finishes. For first time peoples make sure to read and understand the post given below and our OSX86 Basics section. We always recommend to install on a clean hard disk. If you are suffering from endless reboot after leopard hackintosh install, then follow these steps to solve it.

1. Check your BIOS setup and use the following setting if available :

• Set Core Mutil-Proccessing disable (if all goes well set enabled)
• Set ACPI 2.0 Support to yes
• Set ACPI APIC Support to enable
• Set CPU Internal Thermal Control to Disabled or Auto
• Set the Max CPUID Value Limit to Disabled
• Set the “Execute Disable Function” to Enabled
• XD (eXecution Disabled) Disabled

Set ATA/IDE Mode Settings:

• Set Configure SATA as: AHCI
• Set S.M.A.R.T: Enabled

IDE Settings:

• Set ATA/IDE Mode: Legacy
• Set Configure SATA as: IDE
• Set S.M.A.R.T: Disabled

2. Try to Boot using some Darwin Bootloader Switches (or combinations of them):
cpus=1
-f
-x
-v
-legacy
platform=X86PC
platform=86PC
rd=diskXsY (where X is the number of the leopard drive starting from 0 and Y is the number
of Leopard partition starting from 1 example: rd=disk0s1)
see “Darwin Boot Options” for more details

3. if you are using kalyway 10.5.1 then try “TOHKERNEL” at the darwin boot prompt it will boot TOH kernel instead of the vanilla one (this solution is mostly for when the DVD reboots befor getting to the graphical install screen).

4. Make sure you have at least SSE2 Processor.

5. Reinstall OSX86 with minimum options in customization.
 
6. Remove hardware parts you don’t need for the install process (like PCI cards, 1.44, USB deices etc.) 

7. Try to install OSX86 on a blank Hard Disk.

If you are facing any problem during booting or installing Mac OS X or OSX86 or your hackintosh you can identify & troubleshoot the problems with the darwin bootloader commands given below. here we covered almost all of the bootloader commands which you can perform during the initial boot by pressing F8 from the keyboard once you pressed the f8 key you’ll get the access to enter in some special modes like Single User mode, Safe mode and Verbose mode. We tried to cover almost every available option if still we missed any please post a comment given below.

Darwin boot loader level flags, for Darwin version 8.0:-

• -v = verbose mode. Basically tells you wants happening during boot up.System in Verbose mode display a lot of log lines during boot time and does not display the apple gray boot screen, it is good to use this option if things go wrong, or if you get an error screen and you want to know the reason.

• -x = Safe mode. Basically boots your system with the bare minimum kexts. This option boot the system into safe mode ignoring kext cache and loads only necessary kext

•  -s = Single user mode. Command line only mode. Allows you to run commands as root to fix system.This mean you would like to enter “Single User” mode which doesn’t load GUI and doesn’t mount partitions but gives you a prompt so you can make system maintenance and recovery procedures.

•  -f = Tells the hackintosh to reload all kext (Kernel Extensions = drivers) and dump the cache, not rely on it (kext cache found in: /System/Library/Extensions.mkext, you can delete it manually and the system will recreate it)
• cpus= this parameter tells the hackintosh how many cpus to use, for instance if you have dual CPU or dual Core then you can state cpus=2, so the system will use both cpus, and if you get reboot without loading GUI or boot screen then you may use cpus=1 to allow use of one cpu and avoid reboot

• “Graphics Mode” = this parameter tells the hackintosh to use stated graphics resolution and color depth, the pattern to use is: WidthxHeightxDepth@RefreshRate for instance a resolution of 1024×768 with 32 bit color depth and 60 hertz frequancy refresh rate will look like this:

“Graphics Mode”=1024x768x32@60

• config= this parameter tells the system to load using different copy of the boot config file, the default copy used is kept in:

/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

The content of this file state boot options such as:

1. timeout (how much time to wait for user selection in boot prompt)
2. Kernel (what kernel to use)
3. Kernel flags (what kernel flags to use in each and every boot)
4. Quiet boot (weather to display boot menu or not)
5. Boot graphics (if to boot with apple spinning circle)

ACPI Flags are as on :

• acpi=off = Don’t enable ACPI
  
• acpi=ht = Use ACPI boot table parsing, but don’t enable ACPI interpreter
  
• acpi=force = Force ACPI on (currently not needed)
  
• acpi=strict = Disable out of spec ACPI workarounds.
  
• acpi_sci = {edge,level,high,low} Set up ACPI SCI interrupt. EX:
  
• acpi_sci = edgeacpi=noirq = Don’t route interrupts

A kernel panic is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover. You may encountered with a kernel panic while installing OSX86 or Hackintosh. There are plenty of reasons why Kernel Panic occurs some of them are Defective or incompatible RAM, Incompatible or corrupted kernel extensions, Incompatible or corrupted drivers, Hard disk corruption, including bad sectors, directory corruption, and other hard-disk ills and most possible Incompatible hardware. Attempts by the operating system to read an invalid or non-permitted memory address are a common source of kernel panics. A panic may also occur as a result of a hardware failure or a bug in the operating system. In short there are plenty of reasons and resolutions for kernel panic. Here we study three different Kernel Panic case  Apple2PC Described it very beautifully. You can read the Panic errors given below and understand why it happens.

Kernel Panic Example 1:

Unresolved kernel trap(cpu 0): 0×300 – Data access DAR=0x0000000030D6334E PC=0x0000000027B5CD3C
Latest crash info for cpu 0:
Exception state (sv=0x27CA4500)
PC=0x27B5CD3C; MSR=0×00009030; DAR=0x30D6334E; DSISR=0×40000000; LR=0x27B5CD24; R1=0x0D80BAE0; XCP=0x0000000C (0×300 – Data access)
Backtrace:
0x27B5E6C4 0x27B5D82C 0x27B5607C 0x27B45C74 0x002E9A80 0x002EB94C
0x0008C248 0×00029234 0x000233F8 0x000ABEAC 0x8001016C
Kernel loadable modules in backtrace (with dependencies):
com.apple.GeForce(4.1.8)@0x27b3a000
dependency: com.apple.iokit.IOPCIFamily(1.7)@0x1d8f7000
dependency: com.apple.iokit.IOGraphicsFamily(1.4.2)@0×27867000
dependency: com.apple.iokit.IONDRVSupport(1.4.2)@0x2788b000
dependency: com.apple.NVDAResman(4.1.8)@0x278a1000
Proceeding back via exception chain:
Exception state (sv=0x27CA4500)
previously dumped as “Latest” state. skipping…
Exception state (sv=0x1D92D280)
PC=0x9000B348; MSR=0x0200F030; DAR=0x02A8A000; DSISR=0×42000000; LR=0x9000B29C; R1=0xBFFFE900; XCP=0×00000030 (0xC00 – System call)
Kernel version:
Darwin Kernel Version 8.11.0: Wed Oct 10 18:26:00 PDT 2007; root:xnu-792.24.17~1/RELEASE_PPC
panic(cpu 0 caller 0xFFFF0003): 0×300 – Data access
Latest stack backtrace for cpu 0:
Backtrace:
0x000954F8 0x00095A10 0×00026898 0x000A8204 0x000ABB80
Proceeding back via exception chain:
Exception state (sv=0x27CA4500)
PC=0x27B5CD3C; MSR=0×00009030; DAR=0x30D6334E; DSISR=0×40000000; LR=0x27B5CD24; R1=0x0D80BAE0; XCP=0x0000000C (0×300 – Data access)
Backtrace:
0x27B5E6C4 0x27B5D82C 0x27B5607C 0x27B45C74 0x002E9A80 0x002EB94C
0x0008C248 0×00029234 0x000233F8 0x000ABEAC 0x8001016C
Kernel loadable modules in backtrace (with dependencies):
com.apple.GeForce(4.1.8)@0x27b3a000
dependency: com.apple.iokit.IOPCIFamily(1.7)@0x1d8f7000
dependency: com.apple.iokit.IOGraphicsFamily(1.4.2)@0×27867000
dependency: com.apple.iokit.IONDRVSupport(1.4.2)@0x2788b000
dependency: com.apple.NVDAResman(4.1.8)@0x278a1000
Exception state (sv=0x1D92D280)
PC=0x9000B348; MSR=0x0200F030; DAR=0x02A8A000; DSISR=0×42000000; LR=0x9000B29C; R1=0xBFFFE900; XCP=0×00000030 (0xC00 – System call

You should understand that what happened here is that the OS has stopped working since it has a problem, the first thing it does is look for a debugger to pass the control to (since this is not a Mac OS X developer station it will not find one), next thing it will do is dump to the screen all the data it can on the incident so you or a qualified technician can understand what the problem is.

the first part (blue part) display data of the CPU registers, program control exception state for CPU number 0 (this is your first CPU) at the time of crash, this data is hex address in the memory, it will not do you much good unless you are a mega advanced user.

next part Backtrace (green part) also uses hex memory address to point the command the CPU ran before crashing, again will not do us any good.

next part (bolded black) is still regarding backtrace (what happened before the crash), but it tells us what modules (usually kext) where loaded, usually this part can tell us allot, since this loading sequence ended with crashing the OS. in this section we see the last loaded module (in this example the GeForce) and the modules it depends on that needed to be loaded before it so they probably did not cause the crash since they are already loaded (although still possible that they are the fault – but rarely they are).

next part (Red part) is the exception chain, again stating the data as hex memory address and the CPU registers, will not help us.

last interesting part is the kernel version part (orange part) this part will state what kernel you are using, name version build date and platform in this example:

Darwin

8.11.0

oct 10

PPC (Power PC)

Conclusion 1 : The problem is with the GeForce kext.

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Kernel Panic Example 2:

panic(cpu 0 caller 0x001A429B): Unresolved kernel trap (CPU 0, Type 14=page fault), registers:
CR0: 0x8001003b, CR2: 0×00000024, CR3: 0x00d7b000, CR4: 0x000006e0
EAX: 0×00000000, EBX: 0x02bacc00, ECX: 0x025dc9a4, EDX: 0×00000000
CR2: 0×00000024, EBP: 0x14053ef8, ESI: 0×00841684, EDI: 0x0083df64
EFL: 0×00010206, EIP: 0x003bd3b3, CS: 0×00000008, DS: 0×14050010
Backtrace, Format – Frame : Return Address (4 potential args on stack) 
0x14053d38 : 0x128d08 (0x3cb134 0x14053d5c 0x131de5 0×0) 
0x14053d78 : 0x1a429b (0x3d0e4c 0×0 0xe 0x3d0670) 
0x14053e88 : 0x19ada4 (0x14053e98 0x14053ea8 0xe 0×48) 
0x14053ef8 : 0x83df81 (0x2bacc00 0×841684 0x14053f28 0x38073e) 
0x14053f28 : 0x39c536 (0x2bacc00 0x28b9880 0×8 0×2) 
0x14053f78 : 0x13d7d9 (0x28b9880 0×2686021 0×0 0xbffff378) 
0x14053fc8 : 0x19ac1c (0×0 0×0 0×4 0×207) Backtrace terminated-invalid frame pointer 0×0
Kernel loadable modules in backtrace (with dependencies):
com.apple.driver.IOBluetoothHIDDriver(1.7.2b2)@0×8 37000
dependency: com.apple.iokit.IOBluetoothFamily(1.7.14f14)@0x6be 000
dependency: com.apple.iokit.IOHIDFamily(1.4.10)@0×531000

Conclusion 2 : We probably have a problem with the Bluetooth kext. so up to here it was easy and straight forward, the next doesn’t have the loaded module part.

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Kernel Panic Example 3:

Unresolved kernel trap(cpu 0): 0×300 – Data access DAR=0×0000000000000010 PC=0x00000000000819E8
Latest crash info for cpu 0:
Exception state (sv=0x3D849280)
PC=0x000819E8; MSR=0×00009030; DAR=0×00000010; DSISR=0×40000000; LR=0x000819CC; R1=0x2720BB00; XCP=0x0000000C (0×300 – Data access)
Backtrace:
0x00032AC8 0x000823DC 0x00075F58 0×00075918 0x0006B45C 0x0006B730 
0x000578A0 0x0002921C 0x000233F8 0x000ABAAC 0x414C5945 
Proceeding back via exception chain:
Exception state (sv=0x3D849280)
previously dumped as “Latest” state. skipping…
Exception state (sv=0x42AF9280)
PC=0x9000AB48; MSR=0x0000F030; DAR=0x011DB004; DSISR=0×42000000; LR=0x9000AA9C; R1=0xF0101080; XCP=0×00000030 (0xC00 – System call)
Kernel version:
Darwin Kernel Version 8.8.0: Fri Sep 8 17:18:57 PDT 2006; root:xnu-792.12.6.obj~1/RELEASE_PPC
panic(cpu 0 caller 0xFFFF0003): 0×300 – Data access
Latest stack backtrace for cpu 0:
Backtrace:
0×00095138 0×00095650 0×00026898 0x000A7E04 0x000AB780 
Proceeding back via exception chain:
Exception state (sv=0x3D849280)
PC=0x000819E8; MSR=0×00009030; DAR=0×00000010; DSISR=0×40000000; LR=0x000819CC; R1=0x2720BB00; XCP=0x0000000C (0×300 – Data access)
Backtrace:
0x00032AC8 0x000823DC 0x00075F58 0×00075918 0x0006B45C 0x0006B730 
0x000578A0 0x0002921C 0x000233F8 0x000ABAAC 0x414C5945 
Exception state (sv=0x42AF9280)
PC=0x9000AB48; MSR=0x0000F030; DAR=0x011DB004; DSISR=0×42000000; LR=0x9000AA9C; R1=0xF0101080; XCP=0×00000030 (0xC00 – System call)
Kernel version:
Darwin Kernel Version 8.8.0: Fri Sep 8 17:18:57 PDT 2006; root:xnu-792.12.6.obj~1/RELEASE_PPC

Conclusion 3 :

1. first option is a random memory access error, meaning that the memory has been accessed to an area that wasn’t expected or allowed, maybe even an application has written into memory that it shouldn’t have (that was not its space) and by that caused the OS/kernel to crash, you should check what recent applications/utilities/kext/bundle/plugin/login items you have installed and remove it or disable its launch for a while until you can sort it out.

2. second option is usually the case for real macs but also possible for PC, as simple as a hardware problem, or bad memory card that causing the problem, maybe it act badly only if it is cold (immediately after booting the machine) or when it is hot (after several hours of work, depends sometimes minutes is enough on a sunny day), another hardware problem can be any hardware that access memory asynchronously, like IO (bluetooth card, modem, wifi, network card, etc.).

3. another option is that your combination of kext and bundles is not working (maybe versions of them some are older then should be?) so for such a case i always keep a bootable/loadable System/Library/Extensions folder on the disk.

4. this option is rarely the case, but can happen, if the main boot partition doesn’t have enough free space it could cause the problem, so all you need to do in this case is to boot in safe mode and free some space.

5. another simple option is the case of a kext/application/kernel trying to access a file that it doesn’t have a permission to access to, this can be caused due to wrong unix file mod, in this case boot into single user and fix permissions.

6. last option (that i can think of) is a bad kernel, so since the kernel itself is badly behaving that is why there are no kext loaded yet, since the kernel hasn’t finished loading the core. this is why i keep a spare bootable/loadable copy on the disk so i can boot from it on a rainy kernel problem day.

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Terminal  is a terminal emulator included in Apple’s Mac OS X operating system. Terminal is designed for you to typing in specific commands that you would not be able to do otherwise. This is great for customizing your Mac and unveiling hidden features.It originated in Mac OS X’s predecessors, NEXTSTEP and OPENSTEP, and allows the user to interact with the computer through a command line interface. You can find the Terminal in the Utilities folder within the Applications folder. Open the Terminal program, which you’ll find in the Applications_Utilities folder. Once launched, Terminal opens a single window displaying a greeting and a second line of text that comprises the prompt. With that window active, anything you type will enter just before the rectangular cursor that follows the prompt. After you type a command, simply press Return or Enter to run it. Here we listed some vey basic commands you must know. These commands are very useful for your daily Mac Adventure.

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• Login as Root

“ sudo –s ”

After typing that, it will prompt you for your user password, assuming you’re on an administrator account. Once you are accepted, you can do the rest of these commands.
OR:
“ su “, which asks for the root password. If you don’t have the root user enabled, follow the directions below. NOTE: Enabling the root user can be dangerous.
Again, after typing that, it will ask for the root password.

• Change root password
  If you don’t like your root password, use:

“ sudo passwd root “

Then type in your old root password, then give it a new password. If you had no root password before, it will simply ask you to enter a new password. 

• Change directories
  To move around in the various directories, use cd. Example:

“ cd /applications “

That will move you into the applications folder.
Typing cd with no argument will return you to the directory you were in before.
To change to a directory with spaces in the name, surround the directory name in quotes Example:

 “ cd /Applications/”XChat Aqua”

That will move you into a folder called XChat Aqua in the applications folder.

• Move to other volumes/disks/partitions
  To move to different volumes/disks/partitions, use cd again Example:

“ cd /volumes/Mac “

That will move you into the root (/) directory of the volume named Mac.
You can also change to a volume with spaces, much like the last hint Example:

“cd /volumes/”Mac OS X”

• Remove a file from your Mac
  This will remove a file from the same directory you are in:

rm <filename>

Example: “ rm something.txt “

You can specify a path to a file to delete, if it is in a different folder.
rm /path/to/something Example:

 “ rm /Applications/Candybar.app “

This will remove the application Candybar from your applications folder:

This will remove a directory/folder on your Mac:

rm -d <folder>
Example: ” rm -d delete_me “

(Say you had a folder called delete_me in /, your start disk’s main folder)
Note: You can specify a path for this too, like the previous rm commands.

• Copy a file
  To copy a file, use:

cp <filename> <name_of_copy>
Example: “ cp something.txt somethingelse.txt “

This will make a duplicate of something.txt and name it somethingelse.txt

• Move a file
  To move a file, use:

mv <filename> <destination>
Example: “ mv something.txt /Applications “

This will move something.txt to the Applications folder.

• Find a file
  To find a file, use:

locate <filename>
Example: “ locate Callisto.kext “

This will look for anything related to Callisto.kext on your system.

• Find a binary file
  To find a binary file, like rm, use:

whereis <binary file>
Example: “ whereis rm “

This will look for the rm command.

• Create a folder
  If you want to make a folder:

mkdir <name_of_folder>
Example: “ mkdir directory “

Will make a folder called directory in the current folder you are in.

• Move a folder
  If you want to move a folder:
  mv folder_name path Example:

 “ mv folder /applications “

Will move a folder called “folder” to applications.
NOTE: You can also specify a path if you want to put the folder somewhere specific. Example:

mkdir /Applications/directory

• Repair Permissions of a folder
  If you’ve been naughty and messed with the System/Library/Extensions folder at all, you can repair the owner and permissions of the folder by doing:

chmod -R 755 <path>  
chown root:wheel <path>

Example

“ chmod -R 755 /System/Library/Extensions “
” chown -R root:wheel /System/Library/Extensions “ 

• Repair permissions in Terminal without DiskUtility
  To repair permissions on your whole system without the need of disk utility, do:

“ diskutil repairPermissions / “

• List Files in a directory
  If you want to view files in a folder, do:

“ ls “

Kexts, or kernel extensions are drivers that are installed to /System/Library/Extensions/.Kext files often have the “.kext” extension and allow for extra hardware support and and in the case of OSx86, to replace Appleʼs original drivers with ones that are optimized for use on PCs. Leopard holds kext files/folders in the /System/Library/Extensions folder, at boot time the relevant kext are uploaded from Extensions.mkext this is a cache folder that contains kext related to the installed hardware. If you loves your hackintosh then take a full backup of your kexts because some kexts may disappear after the update procedure.

For making backup of your Kexts open Terminal and type in these commands:

sudo -s
[enter password]
cp -r /System/Library/Extensions /System/Library/Extensions.backup
cp -r /mach_kernel /mach_kernel.backup

For restoring your Kexts open Terminal and type in these commands:

sudo -s
[enter password]
cp -r /System/Library/Extensions.backup /System/Library/Extensions
cp -r /mach_kernel.backup /mach_kernel

Kext file is a kernel extension. They’re generally used for device drivers and other things that need to modify the system at the lowest level. They’re not the same as classic Mac OS extensions, as many of the things that classic Mac OS extensions did are done differently in Mac OS X.Since kernel extensions aren’t protected by Mac OS X’s memory protection, developers are encouraged to stay away from writing them unless they absolutely have to. Even then, Mac OS X can dynamically load them, so chances are you’d rarely have to add anything to Mac OS X’s Extensions folder.

What is KEXT?
KEXT stands for Kernel Extension, this means that whatever needs to run in the kernel (OS core) environment can be written as extension and then loaded, even after the OSX has finished loading, this mostly answer the needs for hardware drivers.

Where are kext located?
kext are not files rather a folder (disguised as a file),

Leopard holds kext files/folders in the /System/Library/Extensions folder,
at boot time the relevant kext are uploaded from Extensions.mkext this is a cachefolder that contains kext related to the installed hardware,

you can delete it, if Leopard can’t find it, it will create it again,

you can also state to rebuild it from darwin prompt at boot time using the switch -f see this post for further information.
How to Install a new Kext?

cd /System/Library/Extensions
mv KextName.kext KextName.old  (where kextName stands for the kext you want to replace)this will rename the kext and this way back it up, it is highly recommended, warmly advised, very important to follow this step, it saved my OS many times

cd /path/to/new/kext (put your downloaded kext path here)
cp -R KextName.kext /System/Library/Extensions

next you need to fix permissions so the kext can be executed by OS user (root/system)
cd /System/Library/Extensions
chmod -R 755 KextName.kext
chown -R 0:0 KextName.kext   (this will set the ownership on files to system user (root))
rm /System/Library/Extensions.mkext   (this will reset all kext caching done by OSX)

This guide is prepared for newbees of OSX86 who are interested to run OSX on their ordinary P.C. but not aware with OSX dictionary. Most of migrator comes from Windows platform & never heard about Kernel,Kext,Vanilla etc. Forums are the best place for finding information.I have collected some information from the major OSX86 sites about these basic terms lets take a quick look. 

Q.    What are kexts ? 

Ans. Kexts, or kernel extensions are drivers that are installed to /System/Library/Extensions/.Kext files often have the “.kext” extension and allow for extra hardware support and and in the case of OSx86, to replace Appleʼs original drivers with ones that are optimized for use on PCs. 

Q.    What is a kernel ? 

Ans. A kernel is in short terms the “core” of the operating system. It controls basically all low level operating functions. Kernels exist in all Linux and UNIX based systems, including Mac OS X. In Mac OS X the kernel is located in the root of your hard drive (/) and is named “mach_kernel” by default. If you have a vanilla based system (see below) then replacing the kernel is most likely not necessary, however if you have an AMD or SSE3 incapable processor then a patched kernel will likely be required.

Q.    What is DSDT ?

Ans. DSDT is a part of ACPI. Actually DSDT tells OS how to interract with the hardware (simplified way of telling it). OSX has an incomplete ACPI implementation which supports only a subset of DSDT. By replacing DSDT we can declare essentially the same interface but in the way that OSX understands. This potentially can solve nearly any ACPI-related problem (except if OSX bypasses ACPI). Other usage case is emulating by the means of DSDT features or hardware components not present on your system. But this is limited to devices that use ACPI.

Q.    What is DSDT patching? 

Ans. This is an area very rarely delved into, and is something that some of even the most experienced users dare not venture. In reality, its not dangerous, it just can be painfully hard at times. DSDT is a table found in your computerʼs BIOS that controls ACPI (power, time, etc.) functions. Starting at OS X 10.5.6 Apple decided to start checking for faulty DSDTs when it boots. Obviously the PCs DSDT comes back as faulty so it will not boot. The only way to counteract this is to make a dump of the DSDT in the BIOS and patch it properly for Darwin. First of all, you need a modified bootloader that will support DSDT override. This installer includes just that, using the “Install PC_EFI v9 Chameleon Edition 1.0.12” checkbox. Now you need a patched DSDT file that will be copied to / dsdt.aml. To create DSDT dumps you can use the DSDT Patcher (also included in the Extras folder) but this is an advanced method, and often UOI plugins will include a DSDT file that you can install easily with this installer. However beware, even if you have the same motherboard DSDTʼs can vary by BIOS version so try to make sure that you have the same BIOS version as what is specified in the plugin.

Q.   Difference between SMC & RTC ?

Ans. The SMC is basically System Management Controller. By resetting the SMC you can resolve some computer issues such as not starting up, not displaying video, sleep issues, fan noise issues, and blah-2. While The Real Time Clock (RTC) is a chip on the logic board that controls the date and time functions of the computer. If the computer is experiencing a booting issue, resetting the RTC may resolve it.

Q.   What is a vanilla compatible system ?
Ans. A vanilla compatible system is a computer capable of running OSx86 with minimal modifications (no patched kernel, compatible with Apple software updates). You have a vanilla capable system if: you have a Core 2 based processor. 

Q.   What is EFI emulation ?
Ans. EFI is the Extensible Firmware interface found in real macs. EFI is basically the “BIOS” of a Mac. For a computer to be properly recognized as a mac and to have the most compatibility it must have EFI. The problem here is that PCs do not have EFI.Developers have counteracted this problem by using EFI emulation which enables basic EFI function calls through a specially modified bootloader. EFI distributions for OSx86 include PC_EFI and Chameleon. Nearly all OSx86 installs have some form of EFI emulation installed, so this is not necessarily something to worry about. EFI emulation is required to use vanilla (unpatched) kernels and kexts, and to use GUID partition maps and EFI strings (more on that below)

Source’s PCWIZ , Insanelymac , Netkas , Leo4all