Memory Maximum: 64 bit kernel vs 32 bit kernel

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Level 1

24 points

Memory Maximum: 64 bit kernel vs 32 bit kernel

Just observed that when I'm in 64 bit kernel mode, I can access all 48 GB RAM installed in my system (6X8GB DIMMs).

In 32 bit kernel mode, only 32 GB is showing up.

Is this a known limitation?

Mac Pro (2010) 2 x 2.93 GHz 6-Core, 48 GB 1333, Mac OS X (10.6.4), ATI 5870, OWC SSD Boot

Posted on Aug 23, 2010 10:38 AM

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Answer 1

The hatter

Level 9

60,980 points

Aug 23, 2010 10:46 AM in response to adamsfbay

Yes, OS X Client limitation in 32-bit mode.
In 64-bit, 64GB is seen.

http://eshop.macsales.com/shop/memory/Mac-Pro-Memory

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Answer 2

Aug 23, 2010 6:16 PM in response to adamsfbay

The 32-bit kernel uses PAE, so it should have 36-bit addressing which should give you up to 64GB. Unless for some reason Apple is limiting the 32-bit kernel.

With that much RAM though, I'd probably be using the 64-bit kernel as the default anyway, unless you have some bit of hardware that refuses to play nice with it.

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Answer 3

adamsfbay Author

Level 1

24 points

Aug 23, 2010 9:48 PM in response to Scott Billings

Yep, Apple is limiting it then to 32 GB in 32 bit mode.

I have to run that sometimes for a PCI card I use, and my corporate VPN (which doesn't like 64 bit at all).

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