Snow Leopard is true 64bit OS but is upgrade automatically set to 32bit?

GARoss · Sep 4, 2009

Maybe this has been covered & I'm not searching with the right words but by updating to Snow Leopard, are we actually running in 64bit? This would make sense at this time because it will take a while for all software support to convert to 64bit. I've run 64bit Ubuntu Linux before & hardware/software support is a real pain. So, when Snow Leopard was announced as 64bit the 1st thing I thought of was it will be a real headache for a while.
Sometimes there's too much info on the net (& misleading info too) & while surfing I ran across several blogs that basically says Snow Leopard by default is still running @ 32bit. I took a quick look @ /Library/Preferences/SystemConfiguration/com.apple.Boot.plist as suggested in this article netkas.org » SnowLeopard and 64-bit. & according to the author, my iMac 9,1 is running 32bit, not 64bit.
So, is Snow Leopard running @ 64bit or 32?

BKRonline · Sep 4, 2009

To see if your mac is running 32bit or 64bit EFI, open up the Terminal and type this:

Code:

ioreg -l -p IODeviceTree | grep firmware-abi

It will return either “EFI32″ or “EFI64.”

Your iMac 9,1 is indeed capable of running 64 bit EFI, I'm not sure exactly what that author you speak of was referring to.

Refer to this blog for for detailed information about the above.

One update about the above link is that Mac OS 10.6 build 10A432 was / is indeed the GM (gold master).

Here's a good blog quote:

It works like this, Snow Leopard is a 64-bit OS, and almost all of its applications are 64-bit, and almost if not all of its frameworks for developers to tap into are 64-bit. There is a part of the operating system called a kernel, it can run in either 32-bit mode or 64-bit mode. There is a lot of code that taps into the kernel for low level device functions, these bits of code are called kernel extensions or kexts, they are written both by Apple and by third parties. 32-bit kexts do not play well with a 64-bit kernel, and as almost all kexts are 32-bit because pre Snow Leopard the kernel was 32-bit, this would cause a huge amount of headache to end users to default to a 64-bit kernel. and most kexts will not see a performance improvement by running in a 64-bit mode.

What are the advantages of running a 64-bit kernel?
The way Mac OS X is designed to take advantage of more then 4GB memory pre 64-bit, causes it to swap address for memory above the 4GB barrier, which in turn makes each memory operation slightly slower. If you have more then 4GB of memory in your computer, running a 64-bit kernel will speed up memory read/write some, but will cause more compatibility issues with kexts. Thats it. If you have less then 4GB of memory a 64-bit kernel will have no advantage what so ever, and above that you will see some performance improvement when more then 4GB of memory is consistently being used. (edited by BKRonline) ... and as it will take third parties some time to write 64-bit kexts, it makes absolutely 100% sense to default to a 32-bit kernel at this point.

I edited the above a little for accuracy about some Macs not being able to have more than 4GB of RAM installed... recently they certainly can!

Hope this helps!

vansmith · Sep 4, 2009

Simply put, you are running an operating system that has a 32-bit kernel with 64-bit applications on top. The only Mac that defaults to a 64-bit kernel is the Xserve. Some other Macs are capable of running a 64-bit kernel but I advise you not to do this for compatibility sake.

GARoss · Sep 5, 2009

Thanks guys. It reads <"EFI64">
So, if Adobe writes their next CS? software for 64bit Mac 10.6 compatibility (they do offer CS4 in 64bit for Vista 64bit/Windows 7 64bit), will I be able to take advantage of the 64bit speed without changing my current kernel mode or would it be a decision on my part to switch to the 64bit kernel mode (as described in the article from my 1st post) & lose compatibility with other software; say printers, Open Office, etc? I hope I'm asking this correctly.

bobtomay · Sep 5, 2009

You will be and are currently able to take advantage of all 64 bit applications on top of the 32 bit kernel.

GARoss · Sep 6, 2009

bobtomay said:
You will be and are currently able to take advantage of all 64 bit applications on top of the 32 bit kernel.

Okay. Suppose I want to install program xyz; a new state of the art graphic program on my iMac9,1. 64 & 32bit versions are available. Are you saying that the xyz 64bit software will preform just as well on top of the 32 bit kernel as it would on the 64bit?

DarkestRitual · Sep 6, 2009

Yes, that is what he is saying. Right now you are capable of running a 64 bit kernel also, but it would be ill advised to do so since most of your kernel extensions are written for a 32 bit kernel. Given time after developers change to include 64 bit compatible kernel extensions, perhaps more macs running SL will default to a 64 bit kernel. However, all macs with a 64 bit processor that are running 64 bit apps are running the apps and taking full advantage of the 64 bit processing power.

GARoss · Sep 7, 2009

That's all that really matters. No harm, no foul; the best of both worlds.
I was curious so I tried the hold down 6-4 key method of booting into 64bit. All my software seemed to work but I couldn't print to my i950 Canon. Like most, there are 1 maybe 2 programs that would benefit in 64bit mode. There's no hurry to go 100% 64bit until those apps are revised to 64bit anyway.
My thanks to all.

DarkestRitual · Sep 7, 2009

Glad to help clear it up.

Snow Leopard is true 64bit OS but is upgrade automatically set to 32bit?

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