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OS X Memnory Limitations

L

liulangzi

macrumors newbie
Original poster
Sep 28, 2009
2
0
Hi

I am totally new to Mac OS, could like to check with you guys.
I planning to buy a MBP, as i look at the specs, MBP can support up to 8GB of ram (2 x 4GB), the question is, i knew that that for MS windows, only 64bit can support anything above 3 GB, how about Mac OS X? say if i do purchase 2 x 4GB, can OS X detect 8GB? or are there an 64bit version instead? :confused:

As i am planning to use VMware Fusion to have a VM running windows concurrently, therefore if OS X can support up to 8GB of memory that will be great!.

Appreciated you guys replies.;)

Thanks!
 
OS X does not sell separate 64-bit and 32-bit versions, but rather kind of rolls them into one. This is more feasible for OS X than it is for Windows since newer versions of the OS can run both 64-bit and 32-bit apps, regardless of whether the kernel is running in 64-bit or 32. (Edit: the guy below me says that the 64-bit kernel can’t run 32-bit apps. But I do know that the 32-bit kernel can run 64-bit apps. The newest version of OS X, 10.6 (or Snow Leopard) is 64-bit. However, on certain machines, it still only runs a 32-bit kernel (however, the apps and processes in the OS still run in 64-bit). I don’t know enough to say whether recognizing more memory requires the kernel itself to be in 64-bit mode, but I suspect it does.

However, I think (but again, I’m not sure, hopefully someone else will chime in here) that all the new machines being sold now, or at least all new MBPs, run OS X with a 64-bit kernel, so you shouldn’t have to worry about a thing.

t.l.;dr. (which means “too long; didn’t read”, so it’s kind of a summary) I’m pretty sure you don’t have to worry about anything, hopefully someone else can confirm.

Also, in the future you’ll probably have more luck getting answers if you use a more descriptive title for the thread. “Os X” is just about as unspecific as you can get in a thread about OS X.
 
However, I think (but again, I’m not sure, hopefully someone else will chime in here) that all the new machines being sold now, or at least all new MBPs, run OS X with a 64-bit kernel, so you shouldn’t have to worry about a thing.
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I don't think so, because 32-bit apps will not run under the 64-bit kernel.

If the laptop says it supports 8GB it should support 8GB of memory.

OSX should support as much memory as you put in, that's the way I see it anyway, I may be wrong, but I've run OSX 10.5 and 10.6 on my Mac Pro, and both detected my 18GB RAM, I'm running in the 32 bit kernel.

Have you thought of buying the MBP with 2GB RAM, and then purchasing 2x4GB RAM from otherworldcomputing.com for the model, I think it's like 40% cheaper than buying it from Apple. + you pay the fee to get the Apple authorized guy to put it in for you.

Kind Regards
 
Hi MythicFrost & devburke,

Thanks for the prompt replies, if this is the case, i would assume that OS-X would be able to support 8GB of memory. As on MBP specifications page, refers to hardware able to support up to 8GB.

Ya i am thinking o purchasing the 2GB model and upgrade through 3rd party reseller.

Thanks!
 
At this point in time, no system (save the Xserve) running Snow Leopard does so with the 64-bit kernel by default. 64-bit apps run fine under the 32-bit or 64-bit kernels. 32-bit apps run fine under 32-bit or 64-bit kernels.

When running the 32-bit kernel, PAE is enable which allows the system to address more than 4GB of RAM. No single 32-bit application or process can address more than 4GB of RAM.

S-
 
MythicFrost said:
Really? What's the actual point of having the 64-bit kernel?
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Yep. Well, a 64-bit kernel allows a 64-bit app to fully leverage the memory capabilities without running into the per-process limit as well as avoid the need for the PAE hack.

Apple isn't going to all this work for the gradual transition over time ever since 10.3 for 'it's cool' reasons. :D Consider where the Mac is well-positioned: media editing. That can easily eat up huge gobs of memory, right where full 64-bit support easily pays early dividends.
 
Basically, 32/64 bit apps work fine on either kernel. 32 bit kernel will limit it to 4GB of memory per thread (regardless of 32/64 bit). 64 bit kernel will allow 64 bit threads to use more than 4GB of memory. 32-bit threads will never ever use more than 4GB of memory, regardless of kernel.

OS X can recognize more than 4GB of memory, even in Tiger and Leopard. You just couldn't use more than 4GB per thread. SL only allows 64 bit apps in 64 bit kernel to use more than 4GB of memory.

Before, it was a software hack to let you recognize more than 4GB but not use more than 4GB per thread.
 
Shouldn't I be using the 64 bit kernel then? I have 18GB RAM, what if I have an application that wants more than 4GB RAM?

Kind Regards
 
MythicFrost said:
Shouldn't I be using the 64 bit kernel then? I have 18GB RAM, what if I have an application that wants more than 4GB RAM?

Kind Regards
Click to expand...

No, regardless of 32/64-bit kernel, 32-bit apps are limited to 4 GB and 64-bit apps are not. You can read these articles for details on the differences between the 32-bit and 64-bit kernels:
http://www.appleinsider.com/articles/08/08/26/road_to_mac_os_x_10_6_snow_leopard_64_bits.html
http://www.appleinsider.com/article...ard_twice_the_ram_half_the_price_64_bits.html
 
MythicFrost said:
I don't think so, because 32-bit apps will not run under the 64-bit kernel.
Click to expand...
Nonsense.

I think the only issues with 32ibit (with the 64bit kernel) are 32bit kexts and device drivers. You cannot have 32bit device drivers or kexts if you booted into K64.
 
Nonsense.
Click to expand...
I thought that's what I read.

I think the only issues with 32ibit (with the 64bit kernel) are 32bit kexts and device drivers. You cannot have 32bit device drivers or kexts if you booted into K64.
Click to expand...

That's I meant, I thought it was applications, but it's that.

Kind Regards
 
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