Dual Booting Demystified

I have had this question asked to me numerous times and some have suggested that a simple guide would be helpful to them. So here it is, a simple guide to creating a dual boot with OS X 10.6.x & Windows 7 on a single hard drive using the Chameleon bootloader. This is not the only way to achieve this goal but I am going to outline the methods I personally use which are among the simplest and easiest to duplicate.

Disclaimer: Repartitioning your hard drive can and will erase all data contained on it, resizing partitions with a utility like GParted may alter the partition table without destroying data but there is still a significant risk of failure and data loss. I strongly advise you to ensure you have backed up all important data before attempting ANY alteration of your existing partition structure. I am not liable for any data loss due to the (mis)use of this guide, I have warned you of the risks and advised you to make a backup of your data, I am not responsible for your data, you are!

Important Note: There are a lot of people who use GUID partition types for their hackintosh drive. While this arguably has some advantages when using OS X exclusively I personally advise against the use of GUID partition types, particularly when dual/multi-booting. It will only complicate matters and offers NO advantages over a standard MBR partition scheme in my opinion. This guide assumes you are using an MBR partition scheme – if you are using a GUID partition scheme I encourage you to switch it back to MBR or the instructions here may fail. (The instructions here should actually work for a GUID partitioned disk – but I have not tested them so if you choose to attempt it don’t be upset with me if it fails. If you happen to be one of those people who have their heart set on using a GUID partition scheme and you do test this method – please let me know your success/failure so I can include the information in this guide, be sure to include any additional instructions that you used (if any) so I can present the information as accurately and completely as possible.) **Important note: Older operating systems (Windows XP, older versions of linux, etc) will not function on a GUID partitioned device.

Note: This guide assumes you are using fdisk440 – NOT the standard fdisk that ships with OS X. You can find fdisk440 in the Tools bundle of the myHack app or Chameleon bootloader.

Section 1 : Basic Instructions

Step 1) Allocate space. Personally I plan in advance if I have the intention of dual-booting. So when I booted my trusty myHack USB Installer to install OS X on my system I used disk utility to create two partitions, the first being an HFS+ partition for OS X, the second being a FAT32 (MS-DOS) partition which I will later prepare for Windows 7 Installation. Since my drive is 1TB in size I just created two 500GB partitions for simplicity sake but adjust this to meet your individual needs. If you did not plan in advance you have three options, make a backup of your files and reinstall, make an image of your partition(s) and restore it after repartitioning the drive, or use a utility like GParted to resize the partition(s). Resizing partitions can take a very long time depending on how large they are so personally I’d just backup my files and reinstall but you decide what option works best for you.

Step 2) Install OS X. ( Please tell me you know how to do this by now ;p ). Yes, you can also install Windows 7 first but the methodology will be slightly different – I install OS X first so for the sake of this guide you should too. Ensure to boot to OS X and complete the post installation configuration and installation of myHack (Chameleon, pc efi, kexts, etc) to the installation drive and verify that it is booting without the USB drive attached and functioning properly before moving on to step 3.

Step 3) Install Windows 7. This should be fairly self explanatory but I will explain a few of the important details so you don’t get stuck. Boot the Windows 7 Installation DVD, begin the installation as normal. When you get to the “Which type of installation do you want” section choose “Custom (Advanced)” it will then ask you “Where do you want to install Windows” – choose the FAT32 (MS-DOS) partition we created in step 1 and click on “Drive options (advanced)”. Click format. Click OK. Click Next and proceed with the installation as normal. You have to format it with the Windows 7 installer before it will allow you to install Windows 7 on it because Windows 7 requires an NTFS formatted partition which is flagged as active. It will reboot a couple of times during the installation process, you will notice that the system will now boot directly to Windows 7 and you will no longer see the Chameleon boot prompt. After you have Windows 7 setup to your liking and are ready to fix the dual boot move on to step 4.

Step 4) Repair MBR. Windows 7 has infected your MBR… In the past you could simply set the active partition on the drive and it would boot to it but if you were to change the active partition now your system will hang at boot.We have to repair the damage Windows has done… Insert your handy dandy myHack USB Installer and use it to boot your OS X Installation (Boot to the USB Installer but at the Chameleon boot prompt select the OS X installation on the internal hard drive instead of booting to the Installer itself). Actually it doesn’t really matter if you boot the installer or the installed OS as we are only going to be using the terminal to repair the MBR but the internal hard drive boots more quickly and is more responsive in general so I choose it to save time. Once you have booted open a terminal and run the following commands (which I will guide you through step by step).

First lets get a list of the disks in your system so we target the correct one by running the “diskutil list” command.

myHack-Pro:~ Conti$ diskutil list
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:     FDisk_partition_scheme                        *1.0 TB     disk0
1:                  Apple_HFS myHack                  500.2 GB   disk0s1
2:               Windows_NTFS                         500.0 GB   disk0s2
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:     FDisk_partition_scheme                        *8.0 GB     disk1
1:                  Apple_HFS Mac OS X Install DVD    8.0 GB     disk1s1

As you can see I have two disks in my system, /dev/disk0 is the 1TB with two 500GB partitions on it, one Identified as Apple_HFS type and has the name I assigned it (myHack), the other is identified as Windows_NTFS type (This is Windows 7). /dev/disk1 as you can see is the 8GB USB Installer which I used to boot the system. You’re results will be different but the important thing to identify here is the /dev/disk# that contains your OS X & Windows 7 installations and the partition number of each of them, in my case OS X being on /dev/disk0 partition #1 and Windows 7 being on /dev/disk0 partition #2.

Next we are going to write a new MBR to /dev/disk0 by running the “sudo fdisk440 -u /dev/disk0” command. (Replacing /dev/disk0 with the /dev/disk# your dual boot is installed on if different). If this is your first time using sudo on this system it will give you a warning message, ignore it… You will be prompted for your password, enter it and continue.

myHack-Pro:~ Conti$ sudo fdisk440 -u /dev/disk0


Do you wish to write new MBR? [n] y

As you can see it displays a warning that it will update the MBR and it prompts you for confirmation. Enter “y” and hit enter to confirm as I have in the example above.

Now we are going to change the active partition to the one OS X (and Chameleon) is installed on. Run the “sudo fdisk440 -e /dev/disk0” to open the disk in edit mode.

myHack-Pro:~ Conti$ sudo fdisk440 -e /dev/disk0
Enter ‘help’ for information
fdisk: 1>

You are now in edit mode, be careful here one wrong move and you’ll wipe the drive blank and be back to step1! Lets type “print” to view a list of the partitions on this drive and confirm that we are editing the correct drive and set the correct partition to active.

fdisk: 1> print
Disk: /dev/disk0    geometry: 121601/255/63 [1953523055 sectors]
Offset: 0    Signature: 0xAA55
Starting       Ending
#: id  cyl  hd sec –  cyl  hd sec [     start –       size]
1: AF    0   1   1 – 1023 254  63 [        63 –  977027392] HFS+
*2: 07 1023 254  63 – 1023 254  63 [ 977027499 –  976495527] NTFS
3: 00    0   0   0 –    0   0   0 [         0 –          0] unused
4: 00    0   0   0 –    0   0   0 [         0 –          0] unused
fdisk: 1>

Ok so as we can see here partition 1 is HFS+, partition 2 is NTFS and that little asterisk before the 2 (*2: 07 1023 254  63 – 1023 254  63 [ 977027499 –  976495527] NTFS) means that this partition is flagged as active, if we were to reboot right now Windows 7 would boot as a result. We want that active flag to be on partition #1 so OS X / Chameleon loads and lets us then choose which of the partitions to boot from a nice graphical menu. Now that we have properly identified all the partitions lets type “flag 1” to flag partition 1 as active. (Change the “flag #” partition number if your configuration is different!)

fdisk: 1> flag 1
Partition 1 marked active.

Done, now all we have to do is write the changes to the disk and reboot the computer. Type the “quit” command to write the current MBR to disk and exit fdisk440.

fdisk:*1> quit
Writing current MBR to disk.
Device could not be accessed exclusively.
A reboot will be needed for changes to take

Step 5) Finish. Thats it, you’ve done it! Un-mount and remove the myHack USB disk and reboot the system with the internal disk. If all has gone well you will be greeted by the Chameleon boot prompt and you can easily select between OS X (which will be the default option) and Windows 7. Congratulations! Continue onto section 2 to learn more.

Section 2 : Troubleshooting & Multi-Boots


Section 2:a – Time synchronization

This is the most common problem that will be encountered when dual booting or multi booting with OS X on a PC. OS X sets your hardware clock to UTC (Coordinated Universal Time), windows and many Linux distributions on the other hand typically default to setting your hardware clock to “Local Time”. The “time zone” you are located in is considered local time – for example I am personally located in the UTC+9 time zone so when I set my clock in OS X it sets the hardware clock to UTC time (which will be 9 hours earlier than my local time). When I reboot into Windows or Linux they will assume my hardware clock is local time thus the clock will now be displaying UTC time which is 9 hours off from my local time. Fortunately this is very easy to resolve.

Part 1) Windows

To correct this problem in Windows 7/Vista we will need to edit the registry. Note: These instructions will not work for Windows XP.

At the windows desktop do the following:

If you would rather not edit the registry manually simply download and run this utcfix.reg file I created to import the data directly into your windows registry.

Windows 7 UTC Registry Fix 1.0
Download Windows 7 UTC Registry Fix 1.0
Downloaded 3162 times.
Size: 299 bytes
  • Exit all Windows-based programs.
  • Click Start, type regedit in the Start Search box, and then press ENTER.
  • If you receive the User Account Control dialog box, click Continue.
  • Locate and then click the following registry subkey:
  • In the right pane, right click anywhere on the empty space and create a new DWORD (32-bit) Value. [NOTE: On 32-bit versions of Windows 7/Vista , you will only see D-WORD]
  • Name it RealTimeIsUniversal [NOTE: This is CaSe Sensitive so make sure it is exactly as shown here.]
  • In the right pane, right-click RealTimeIsUniversal in the Name column, and then click Modify.
  • In the Value data box, type 1, and then click OK.
  • On the File menu, click Exit to close Registry Editor.

This tells windows that your hardware clock is set to UTC and it will adjust for your time zone accordingly (the same way OS X does).

Next simply reboot into OS X and make sure your time is set correctly. The next time you reboot into Windows you should see the correct time – if not ensure that you have properly configured your time zone via the regional and language options in the control panel.

Part 2) Linux

To correct this problem in Linux requires a different process. Not all Linux distributions will be configured to set your hardware clock to a local time zone, some actually do use UTC by default but if you notice a time discrepancy do the following.

First we are going to open /etc/conf.d/clock in a text editor. In this example I will be using nano but if you do not have nano you could also use vi, pico, gedit, kate, or whatever text editor you like.

Open a terminal and type the following to open the file:

sudo nano /etc/conf.d/clock

(type your password)

Find the CLOCK= value.

It will likely appear as follows:


Change it to:


Save your changes and exit your text editor… (In nano it is ctrl+o to save changes and ctrl+x to exit.)

Now before we reboot we should make sure that we have set the correct local time zone. You may do this with a GUI tool… I do the following in my own flavor of Linux, it should apply to many but not all Linux distributions – consult your own distributions documentation if the following does not apply to you. I will be using my own time zone in the following example, you will have to adjust the commands to apply to your own location.

First you will want to locate your own time zone file in /usr/share/zoneinfo. I am in UTC+9 (Korean Standard Time) so my time zone file is located in /usr/share/zoneinfo/Asia/Seoul

Copy your time zone file to /etc/localtime by running the following command in a terminal.

sudo ln -s /usr/share/zoneinfo/Asia/Seoul /etc/localtime

Now open the /etc/conf.d/clock file back up and locate the TIMEZONE= value and set it to your own local timezone, for example mine looks like this:


Save changes and exit your text editor. Now you should be all set to reboot.

Section 2:b – Windows BSOD when AHCI mode enabled

This issue typically arises on windows installations that existed before enabling AHCI mode in the bios. The cause of this issue is the AHCI driver (Msahci.sys) in Windows 7/Vista being disabled. This driver must be enabled before you change the SATA mode of the boot drive.

Why would the Msahci.sys driver be disabled?

During the Windows 7 or Windows Vista installation process, any unused storage drivers are disabled. This behavior speeds up the operating system’s startup process. When you change the boot drive to a driver that has been disabled, you must enable the new driver before you change the hardware configuration.

How can I enable the Msahci.sys driver?

Well first you will have to disable AHCI mode in your bios temporarily to be able to get back into Windows… Go ahead and boot windows normally (it may prompt you to load recovery console because it will have detected that there was a BSOD the last time you attempted to boot the OS, you do not need to enter the recovery console so select boot windows normally and continue). After you get to the windows desktop do the following:

If you would rather not edit the registry manually simply download and run this ahci.reg file I created to import the data directly into your windows registry.

Windows 7 AHCI Registry Fix 1.0
Download Windows 7 AHCI Registry Fix 1.0
Downloaded 659 times.
Size: 278 bytes

  • Exit all Windows-based programs.
  • Click Start, type regedit in the Start Search box, and then press ENTER.
  • If you receive the User Account Control dialog box, click Continue.
  • Locate and then click the following registry subkey:
  • In the right pane, right-click Start in the Name column, and then click Modify.
  • In the Value data box, type 0, and then click OK.
  • On the File menu, click Exit to close Registry Editor.

After you have edited the registry (or imported the ahci.reg file I provided above) you will need to restart your computer, go back into your BIOS setup and re-enable AHCI. When you login to Windows again, you’ll notice the installation of drivers for AHCI. Another restart will be required to finish the driver installation.

Section 2:c – Multi-Boot Configuration

This section will eventually focus on configurations that involve more than just OS X 10.6 and Windows7. I intend to add a linux example to this section as soon as I have some more time to work on it.


It is my hope that this tutorial will help you to easily setup your own dual boot and that it will also help you to understand the underlying principals involved.


– Conti

105 thoughts on “Dual Booting Demystified

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  5. Nice write-up. As for choosing MBR partition table over GPT, I can think of one advatange of choosing a GPT table, it allows for more than 4 partitions on the drive which MBR limits you to. So if you install Windows 7 on your drive, you are already out 2 partitions, one for the system reserved partiton. A downside for choosing GPT, is you can not install Windows 7 on a GPT disk because Windows will prompt about the drive being formatted GTP, and will not install. I have heard that if your system supports UEFI 2.0 then this is not a problem, but I can not confirm this. Once again good write-up.

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  7. Next command works :
    myMac-Pro:~ xx$ open /Users/xx/Desktop/fdisk440

    And that one with sudo doesn’t work :
    myMac-Pro:~ xx$ sudo /Users/xx/Desktop/fdisk440

    • Have you ensured it has executable capabilities?

      chmod +x /Users/xx/Desktop/fdisk440

  8. Hi Conti, thanks for the Handbook!
    I have the next problem – OS says cannot find fdisk440.
    I did copy it from USB to the Application folder, moved it ti the Desktop or Utilities folder, this is the result when I type sudi command :

    myMac-Pro:~ op$ sudo /Users/xx/Desktop/fdisk440 -u /dev/disk0
    sudo: /Users/xx/Desktop/fdisk440: command not found

    this is the case when fdisk440 is on the Desktop
    Any idea ?
    Thanks !

  9. Wow, it seems so easy here. I need xp on my machine for some older software and tried your method. Something in the differences betweeb 7 and xp made it not work. I scrapped the idea and figured I would just install xp on a different hd and use the f8 boot selection if I need to run the pc but I can not get the xp installer disk to properly recognize the hd. I’ve reformatted the extra hd to mbr and fat32 thinking that I would get to the part in the install that asks me to reformat the drive. but it doesnt happen. It tells me that the hd cant run xp. I’ve tried different disk’s and had no luck. I cant believe I’ve de-pc’d my unit that much. Any ideas? Thanks

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  14. Nevermind, I am redoing it according to your guide as we speak.