SnowLeopard and 64-bit.

It looks like not all users understand  about 64-bit support in snow leopard.

So, here is how it works:

on all Macs, except xserve, system boots by default 32-bit kernel.

This kernel can run 64-bit apps justs fine on core 2/core i7 based cpuz.

64-bit kernel works only on macs with 64-bit efi, this is limitation set by Apple,

technicaly 64-bit kernel can be launched by 32-bit efi just fine.

also Apple disabled 64-bit kernel support for any macbooks, even  with 64-bit efi.

64-bit Kernel can run both 32 and 64 bit apps.

On hackintosh only cpus with ssse3 can run 64-bit kernel/apps, its core2/corei7 based cpus.

if kernel is 64-bit, then it can load only 64-bit kexts.

if kernel is 32-bit, then it can load only 32-bit kexts.

Userspace program cant load plugins with other architecture, for example menumeters will work only when you booted legacy, so menubar created by 32-bit application.

Quicktime uses InterProcess Communications(IPC) to load 32-bit codecs in 64-bit player.

64-bit safari uses IPC to load 32-bit flash player plugin.

To try to boot x86_64 kernel on Macintosh,  edit this file:


find there:

<key>Kernel Flags</key>

and change it to

<key>Kernel Flags</key>


  1. September 17th, 2009 | 12:35 am

    […] Snow Leopard’s 64-bit processing is being over-sold.  Unless you have a MacPro, or a recent-model iMac or MacBook Pro, the chances are that your hardware can’t address all of the extra memory.  In theory, the double word length of a 64-bit operating system should yield some benefits, but only if the applications are also compiled to run in 64-bit mode – and it won’t be a huge performance increase.  Many applications aren’t yet compiled for 64-bit, including the most memory-hungry application that many digital photographers use – Adobe Photoshop (although Lightroom is).  On the other hand, if you’re buying a new Mac, put as much memory in as you can (third party memory is generally less expensive than the memory that Apple will sell you) but, also, be aware that Snow Leopard’s 64-bit mode needs to be activated manually at startup (although a third party startup mode selector is available) and may not even apply to your hardware, even if you have a 64-bit CPU. […]

  2. September 26th, 2009 | 12:21 am

    […] 1) Here is a link on how to make 64-bit a permanent boot mode: […]

  3. Michelasso
    September 28th, 2009 | 4:59 am

    Hi Netkas,
    I have a MacBook 2,1, with EFI 32. I eventually managed to install Cham 2 RC3 with boot 10.1 in a USB Pendrive and have it showing pressing option at the boot time. Still OSX boots in 32 bits. I also use the kernel startup mode selector to chose 64 bits, nothing.

    Now it’s not clear to me anymore. I thought that Chameleon + PCEFI were supposed to substitute the Mac EFI and load straight the mach_kernel file in the desired arch (64 bits by default): What am I doing wrong? Has anyone been able to boot the 64 bits kernel with an EFI 32?

  4. font9a
    October 8th, 2009 | 7:49 am

    It’s probably been mentioned before… but 64-bit kexts won’t give you ANY benefit unless you have TERABYTES of RAM that your *kexts* are using.

    Booting into 64-bit mode kernel has absolutely no performance or stability advantage over 32-bit mode. In fact, you’ll probably see LESS performance because drivers haven’t been all that optimized for 64-bit, and 64-bit just has a lot of overhead for almost everything a driver does.

    Case in point: on my MBP 4,2 2.6Ghz, 6GB RAM, 512M 8600GT, 256GB Corsair SSD 240MB/s Read & 200MB/s Writes, screen redraws and finder operations (icon refreshes) are MUCH faster in 32-bit mode than 64-bit mode. I’ve been testing this since SL was officially released and it’s the darned truth.

    Lightroom 2.5 64-bit is every bit as fast in 32-bit kext mode as in 64-bit, if not faster, since screen redraws are faster. I can easily load every single adobe CS4 master suite app, every microsoft office 2008 app (incl entourage), every mac pro app, every ilife app, etc. and get (nearly save a couple hundred MB for the OS) all 6Gb of RAM committed — so 64-bit does not enable you to use more than 3GB system RAM like Windows does. 32-bit does just fine (even better) (up to 64GB I think?)

  5. font9a
    October 8th, 2009 | 7:55 am

    I might also add that iPhone tethering will not work in 64-bit mode (but will work just fine in 32-bit kext mode, once you have it set up correctly).

  6. October 8th, 2009 | 3:12 pm

    […] explicación la he encontardo en  un post de Samuel Campos, creado originalmente por, muchas de las dudas que se me han planteado estaban ya resueltas en los comentarios, esto me […]

  7. matylda
    October 23rd, 2009 | 6:21 pm

    Hi I have a proble I just can find in Library/Preferences/

    the SystemConfiguration

    all the files.plist are in preferences and also there is no

    so I created one

    but it still boot in 32

  8. October 24th, 2009 | 2:29 pm

    So, what’s the advantage in boooting up as 64 bit? I don’t use Safari and I’m not sure iLife 09 or FCE 4.0 can use 64 bit. AFAIK, I have no other apps that are 64 Bit unless it is something native to 10.6.1. So What’s the deal?

  9. Sherif ElShamy
    October 27th, 2009 | 9:18 pm

    i tried this method to boot in 64bit mode and it worked normally but everytime i restarted or shut down my machine all motherboarf settings reset, do anyone have any idea how to pass this problem

  10. FrenchPhil
    October 28th, 2009 | 4:59 pm

    There is a thread on InsanelyMac about MB settings reset. Known as a Snow Leopard problem with Gigabyte MB.
    The workaround is to patch a DSDT.aml.

  11. konteudos
    November 9th, 2009 | 5:25 pm

    Thanks !!

    I used this to start always in 32bit mode , because in 64bit mode my usb WIFI do not work 🙁 so now I am booting in 32 bits and with wifi support 🙂

    used arch=i386


  12. December 21st, 2009 | 5:24 pm

    […] were worried about being stuck in the slow lane with a 32-bit EFI quickly discovered the various workarounds for booting the x86_64 kernel on a 32-bit […]

  13. January 2nd, 2010 | 4:45 am

    I Bought a New Mac Pro 2,1 (8 Core 2007) The Mac Pro 2,1, with EFI 32. was not what Apple said it was I needed 100% 64Bit I/Os & Data paths I hate so much is that my machine I was told was 100% 64Bit is NOT! Apple I will not pay you to go from a MacPro 2,1 (first dual-cpu, quad-core MacPro) to a MacPro 4,1 (Nehalem x 2) You lied you need to step up & deal with your LIE I feel I am owed a TRUE 64Bit Mac Pro no hacks no oh thats older YES Apple it is if you did not Lie to me telling me YES 100% 64 BIT, I would NOT have bought it! I feel false advertising is NOT RIGHT YOU OWE ME MY MONEY BACK OR A REPLACEMENT NOW you should be sorry you tricked me & lucky I don’t Join a Class Action suit. I am so MAD!

  14. January 25th, 2010 | 4:01 pm

    The original 13″ Unibody MacBooks (i.e before they were rebadged as “Pro” machines) *will* boot a 64bit kernel, but it requires a little bit of hacking in order to make it happen:

  15. February 15th, 2010 | 1:43 am

    Joshua Ochs: Thank you for debunking.
    I have a blog article on this history:

  16. sam
    March 21st, 2010 | 2:59 pm

    I also had issues with iPhone not syncing properly when booted up in 64-bit.. Might want to hold off on that until Apple release the next update to SL.

  17. Jackobyte
    April 21st, 2010 | 6:23 pm

    Any update on the iPhone sync issues? Also why would the Internet Tethering not work, is it something to do with the Apple Mobile Device driver not being 64-bit compatible? I mean surely on a regular Mac this issue doesn’t exist, does anyone know how we can get this to work, this is the only issue I have 🙂

  18. Emmanuel rm
    May 19th, 2010 | 4:28 pm

    Hola, tengo una macbookpro de 13 pulgagas, la ultima en el mercado, y cuando voy a ejecutar el programa -32- or 64-bit Kernel Startup Mode Selector- para que corra en 64bit me aparece como icono una x y signo de corrección, entonces esto indica que mi equipo si puede correr en mac, nose que hacer? lo que se es que no me deja colocarlo a 64bit, porque me da un error código 5000

    que hago¿? esperando que puedan ayudarme, me despido, saludos.

  19. Dukowsky
    August 26th, 2010 | 2:54 am

    In this case what should i do? i don’t understand very well but i was trying to process with this instructions

    Edit this file:

    Change this:

    Kernel Flags

    To this:

    Kernel Flags

    But this is what i found on my file.


    bplist00”YBoot LogoVKernel\Kernel Flags_)\System\Library\CoreServices\BootLogo.png[mach_kernel[arch=x86_64 -Ye

  20. Dukowsky
    August 26th, 2010 | 3:02 am

    i don’t know if this is the correct setting but i want to know before do any change in this file. I have a core 2 duo and EFI64 and (imac11,1) that was the result of “Kernel Startup Mode Selector”

  21. Dukowsky
    August 26th, 2010 | 3:18 am

    Hi all i was trying to process with this instructions

    Edit this file:

    Change this:

    Kernel Flags

    To this:

    Kernel Flags

    But i found this in my “”

    bplist00”YBoot LogoVKernel\Kernel Flags_)\System\Library\CoreServices\BootLogo.png[mach_kernel[arch=x86_64 -Ye

  22. ptesone
    October 18th, 2010 | 9:38 pm

    will -force64 be the same as arch=x86_64 ?

    just curious. . .

    running snow leopard 10.6.4 AMD Phenom Hackintosh on 750a nForce

  23. January 11th, 2011 | 3:55 pm

    […] EFI chipset are prevented from loading the 64-bit kernel, although there are claims that this is an arbitrary decision by Apple rather than a technical concern, with a hack using the Chameleon boot loader devised to […]

  24. wahid
    July 14th, 2011 | 6:30 pm

    hi gyz! i have a sony vaio laptop based on 64 bit system, i wanted to run snow leopard on it through VMWare but it did not run and gave this error “A virtual CPU has entered the shutdown state. This would have caused a physical machine to restart. This can be caused by an incorrect configuration of the virtual machine, a bug in the operating system or a problem in the VMware Workstation software. Press OK to restart the virtual machine or Cancel to power off the virtual machine.”

    can any body help me with this please???

  25. tangles
    September 7th, 2011 | 12:20 pm

    I have a 2006 Xserve. Therefore 32bit EFI.

    How would I go about trying to get this to boot 64bit? rEFIt?


  26. May 25th, 2012 | 12:31 pm

    This was an amazing site that I had never seen it before. Thanks a lot for the information because I had liked it very much!

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