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I'm running an Early '11 MacBook Pro with 16GB RAM.

Currently, OS X Lion runs in 32-bit mode by default, and an important piece of software I use for work requires this mode (Cisco VPN client). Most of the work I do is inside a VMWare Fusion Windows 7 64-bit VM with 4GB RAM. The RAM upgrade is fairly recent, which is why I am bringing this up now. I've also considered pushing the VM to 6GB or 8GB, but I'm hesitant as I thought VMWare might have problems loading up all that memory in a 32-bit space.

Am I missing out on any performance gains by running in 32-bit mode?

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He says 16 GB of RAM. –  Thilo Apr 27 '12 at 8:08
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up vote 11 down vote accepted

Lion is not meant to be used in 32bit mode. Also addressing more than 4GB ram with 32bit kernel is slower (it uses PAE).

If the only reason of using Lion in 32bit mode is the Cisco VPN client (yuck!) there is a way. Here is an article explaining how to use the native VPN client instead - it's for 10.6, but should work. It's a matter of configuration, not of software. And here is a forum post that pointed to thad solution.

About the Cisco VPN 3000 hardware - yes, it works with iOS and native OSX VPN client in IPSec mode, and it's a matter of software update and configuration. You should be running at least 4.7.2P according to the CISCO field notice. It's stated that it's not supported, but it works. Here is another success story. Make sure that you're using at least OSX 10.7.2.

ps. being tight on money is not always bad, It usually makes people more creative and makes them think and learn new things. Direct your network admin to serverfault, a place I'm sure he will get decent help.

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BTW the Cisco AnyConnect client works in 64 bit mode –  Matteo Apr 27 '12 at 9:29
    
I use the built in VPN Client to connect to all our service Cisco VPN's. Much better than using the AnyConnect or standard Cisco VPN client –  Stu Wilson Apr 27 '12 at 9:30
    
I appreciate the tip, but we use a VPN 3000 Concentrator, and as far as we know that doesn't support the current native Cisco client. It also doesn't work with iOS in IPSec mode. We've tried to push for an hardware upgrade in the budget... but my company is small and moola is always tight. –  Matt Beckman Apr 27 '12 at 16:37
    
Your confidence made me decide to give it another shot at getting the Cisco VPN client to work with the concentrator. I'll report back! –  Matt Beckman Apr 30 '12 at 6:20
    
VPN concentrator needed an overhaul. After two nights of going over the concentrator settings, I eventually was able to reconfigure it to work with the native client. THANK YOU! –  Matt Beckman May 2 '12 at 6:16
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Not really - until you have programs that refuse to run on anything but a 64 bit kernel or programs that need to allocate more RAM than they can in 32 bit address space you can keep running 32 bit on the Mac OS.

Running a 32bit OS instance does not preclude you from running 64bit applications. It's one of the more unusual things about Mac OS X, and very different to the Windows way of doing things where there are specific 32bit/64bit versions with fairly rigid limitations on what you can run.

As such, depending what you use your computer for there are some disadvantages to running in 32bit mode (addressable memory as per a different answer for one) but by and large you are not forced to run everything in 32bit just because your kernel is, and so the disadvantages are considerable less than for other OS.

See the following question/answer on Stack Overflow for more details:

You can have a play with 32 and 64 bit versions of the kernel by looking at the following instructions from Apple*:

If your Mac uses the 32-bit kernel by default, but supports the 64-bit kernel, you can start up using the 64-bit kernel by holding the 6 and 4 keys during startup.

If your Mac uses the 64-bit kernel by default, you can start up with the 32-bit kernel by holding the 3 and 2 keys during startup.

Your Mac will revert to the default kernel the next time you reboot it.

To select the 64-bit kernel for the current startup disk, use the following command in Terminal:

sudo systemsetup -setkernelbootarchitecture x86_64

To select the 32-bit kernel for the current startup disk, use the following command in Terminal:

sudo systemsetup -setkernelbootarchitecture i386

Note: This setting is stored in the /Library/Preferences/SystemConfiguration/com.apple.Boot.plist file and will take effect every time you start up from this disk. If you start up from a different disk, the setting on that disk, or the hardware default, will take effect.

I am not sure why you talk about RAM in the middle of your question there, it doesn't seem particularly pertinent to me, and nor is there a specific question, so perhaps a question edit would be helpful to promote more answers.

(* Instructions for Snow Leopard, but should still apply)

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The comment about RAM was made because MacBook Pro only supports 8GB max from Apple, and before this I was content with 32-bit mode because the largest amount of memory I needed addressed was what I allotted to VMWare Fusion. Now I want to increase the amount of memory I give my primary VM to more than 4GB, which I thought might cause issues. –  Matt Beckman Apr 30 '12 at 6:22
    
Late 2011 macbooks support 16GB (or so Crucial says). –  Sergio Tulentsev May 4 '12 at 5:55
    
Right, sorry, I meant "8GB max according to Apple", as the 16GB I have been using has worked quite well and passed all the memory tests I could throw at it. :) –  Matt Beckman May 7 '12 at 5:37
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