Is my early 2006 iMac 32-bit or 64-bit?

Question

Is my early 2006 iMac 32-bit or 64-bit?

I ask because Mactracker says that it's 32-bit, so does that mean that Snow Leopard would be a waste of time? I thought the whole point was that it's 64-bit, but if it runs in 32-bit mode only then I can't see the performance increase being anything to talk about.

MacBook Core 2 Duo 2GB RAM 2.4GHz and iMac 17inch 2GB RAM 1.83GHz, Mac OS X (10.5.8), iMac is on Tiger 10.4.11, MacBook is on Leopard 10.5.8

Posted on Oct 4, 2009 11:14 AM

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Answer 1

baltwo

Level 9

62,386 points

Oct 4, 2009 11:25 AM in response to Jonathan Mortimer

Run this command in the Terminal app.

*ioreg -p IODeviceTree -w0 -l | grep firmware-abi*

If you don't get this response, with EFI64 in double-quotes, then it isn't:

*| | "firmware-abi" = <EFI64>*

That said, it matters not, SL brings speed enhancements to both 32- and 64-bit machines.

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Answer 2

Oct 4, 2009 11:41 AM in response to Jonathan Mortimer

[This read tells all|http://www.osnews.com/story/22009/SnowLeopard_Seeds_Use_32bit_Kernel_Drivers_byDefault] about which machine does what in regard to Sno and 64-bit. The performance increase from Sno is not large, like for like. In this resgard, if you run a 64-bit program on your machine, it will run in the 64-bit kernel, but that also is what happened under Leo. Truly noticeable performance increases probably would not occur for you until you move to, say, 4 or more GB RAM and could run a 64-bit program rather than a 32-bit one. The increase would occur under these conditions because more of 4 GB of RAM would be available for non-dedicated use under 64-bit versus 32-bit. And, all of this assumes you would be pushing the limit of your RAM under 32-bit. If you are not pushing it, then there won't be much of a performance increase regardless.

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Answer 3

Barney-15E

Level 10

122,126 points

Oct 4, 2009 11:35 AM in response to Jonathan Mortimer

Whether you can boot the kernel into 32-bit or not does not affect the performance increase of all the 64-bit Apple apps that come with SL. However, if you have a Core Duo and not a Core 2 Duo, then you can't run anything at 64-bit. Look at the hardware section of System profiler.

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Answer 4

Oct 4, 2009 11:58 AM in response to Barney-15E

I think it's like this:

1. His machine is an intel. Thus, he runs 64-bit programs via the 64-bit kernel.
2. Whether or not he has 32-bit or 64-bit EFI, he still can't boot into 64-bit kernel mode unless his machine is new enough (believe what the article gives as reasons or not).
3. Only "newer" 64-bit EFI machines, possibly including his, can boot into 64-bit kernel mode (those in the table in the artice).

I think that the words that tend to go around are that one's performance will be the same whether or not he or she can boot into 64-bit mode. You may recall, however, that my [test results challenge this apparent presumption|http://discussions.apple.com/thread.jspa?messageID=10316685&#103166 85]. They suggest the following:

1. 64-bit programs are faster than 32-bit programs whether run in 64-bit or 32-bit mode (sort of understandable--Incremental RAM is available under 64-bit mode, but should the difference be this large?);

2. There is a performance penalty for running 64-bit programs in 32-bit mode (not understandable--64 bit programs are supposed to run essentially the same whether run under the 32-bit kernel or the 64-bit kernel); and

3. 32-bit programs run faster in 64-bit mode than in 32-bit mode (not understandable--32 bit programs are supposed to run essentially the same whether run under the 32-bit kernel or the 64-bit kernel).

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Answer 5

Oct 4, 2009 12:01 PM in response to Jonathan Mortimer

Leo and Sno are the same when it comes to bitness. The only difference WRT bitness is those with 64-bit EFI and "newer" Macs can boot into 64-bit kernel mode. Have you tried starting up holding down 6-4 or done what baltwo said?

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Answer 6

Oct 4, 2009 12:22 PM in response to Jonathan Mortimer

Seems there is more to this than first meets the eye.

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Answer 7

Barney-15E

Level 10

122,126 points

Oct 4, 2009 12:35 PM in response to donv_the_ghost

donv (The Ghost) wrote:
I think it's like this:

1. His machine is an intel. Thus, he runs 64-bit programs via the 64-bit kernel.

I don't think so since the [Core Duo is a 32-bit processor|http://www.answers.com/topic/intel-core-cpu]. Can you run 64-bit apps on a 32-bit processor?

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Answer 8

Oct 4, 2009 12:40 PM in response to Jonathan Mortimer

Yes, there is a lot going on. I have to go now; I'll look back in on this discussion later.

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Answer 9

Oct 4, 2009 12:47 PM in response to baltwo

I get:

+| | "firmware-abi" = <EFI32>+

This just tells me that the EFI (firmware?) is 32-bit, but not anything about the Core Duo processor or other hardware capabilities.

There is nothing under Hardware in System Profiler that identifies the bit of the hardware, 32 or 64, it doesn't even tell me the CPU model number (in fact, there is no CPU information other than "Intel Core Duo", "1.84GHz", 2 cores and 2MB L2 Cache). Mactracker says that this is a "Yonah" T2400 Intel Core Duo.

After a bit of digging I came up with this on the Intel website:

http://ark.intel.com/Product.aspx?id=27235

It states that the T2400 CPU has a 32-bit instruction set, which I take as final proof that it is a 32-bit CPU and (as far as my understanding of computing goes) is not capable of running true 64-bit code in a 64-bit address space. Therefore all Snow Leopard code should run in 32-bit mode (I really don't know how or believe it if someone says that it can run 64-bit applications on 32-bit hardware). I can only conclude that I should expect 32-bit performance, any performance increase over normal Leopard will be from more efficient code and not anything to do with it being 64-bit.

I think my best option would be to wait for a few updates, perhaps by 10.6.5 they will have better 64-bit support, the iMacs will boot into 64-bit mode by default (I know it can be tweaked but that's not the point) and I can expect to see much improved performance from the latest hardware and software.'

One of the things I do that takes a lot of CPU time is video crunching, whether it be converting or iMovie / iDVD. This process is what I am most interested in speeding up, I know there will be no substitute for a faster CPU but I'm hopeful that running in 64-bit mode will help with shifting such large amounts of data around the system.

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Answer 10

Oct 4, 2009 12:42 PM in response to Barney-15E

Well, if what you say is right, then I agree with you. But I think the issue for a core 2 duo is whether or not it has 32-bit EFI (not 32-bit kernel). Got to go now, but I'll check in later. I always appreciate the tone of you comments. 🙂

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Answer 11

baltwo

Level 9

62,386 points

Oct 4, 2009 12:58 PM in response to Jonathan Mortimer

EFI32 indicates, to me, that your processor is 32-bit and not capable of running in 64-bit. SL can run 64-bit capable apps in 32-bit mode. See http://arstechnica.com/apple/reviews/2009/08/mac-os-x-10-6.ars/5 for more details on this.

P.S. See these for the technical descriptions:

http://developer.apple.com/macosx/64bit.html
http://developer.apple.com/mac/snowleopard/64bit.html
http://developer.apple.com/mac/library/documentation/Darwin/Conceptual/64bitPort ing/intro/intro.html

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Answer 12

Oct 4, 2009 12:55 PM in response to donv_the_ghost

The Core Duo is 32-bit, the Core 2 Duo appears to be 64-bit in all of it's iterations. According to Mactracker, the ones used in iMacs up until now are T5600, T7200, T7300, T7400, T7600, T7700, E8135, E8235, E8335, E8435.

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Answer 13

Oct 4, 2009 1:03 PM in response to baltwo

That is like a 64-bit emulation layer then, the applications are not getting the full benefit of being 64-bit, they cannot run natively as the CPU doesn't have the necessary 64-bit hardware.

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Answer 14

Oct 4, 2009 1:13 PM in response to Jonathan Mortimer

Jonathan Mortimer wrote:
The Core Duo is 32-bit, the Core 2 Duo appears to be 64-bit in all of it's iterations. According to Mactracker, the ones used in iMacs up until now are T5600, T7200, T7300, T7400, T7600, T7700, E8135, E8235, E8335, E8435.

Which of these Apple has decided to include a 32-bit or 64-bit EFI with is not mentioned directly in Mactracker, although it identifies CPU Architecture as 32-bit or 64-bit. I gather that the EFI bit-ness may be gleaned from System Profiler as the Model Identifier being iMac8,1 as opposed to iMac4,1 (please correct me if I'm wrong).

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Answer 15

baltwo

Level 9

62,386 points

Oct 4, 2009 1:16 PM in response to Jonathan Mortimer

That is like a 64-bit emulation layer then, the applications are not getting the full benefit of being 64-bit, they cannot run natively as the CPU doesn't have the necessary 64-bit hardware.

And? This doesn't mean that SL is not appropriate for your machine, which was the original query. I maintain that it is; however, it's your choice. SL contains streamlined features, compressed OS files, and other improvements, whether or not you can run the 64-bit kernel.

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