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Pros and Cons of booting my iMac i5 in 64 bit mode?

D

danistyping

macrumors regular
Original poster
Dec 8, 2009
182
170
Boston, MA
I didn't realize that SL automically boots in 32 bit, even on the new iMacs. I have a core i5 with 8 gigs of RAM. Assuming I boot in 64 bit mode today, will my computer now utilize all 8 gigs? Was it only using 4 gigs in 32 bit mode?

Also, will some applications not run if I boot 64 bit? Any other info is greatly appreciated.
 
OS X has been able to fully utilize over 4GBs for long time. 64-bit mode isn't recommend as some drivers are 32-bit so it might cause you troubles.
 
danistyping said:
I didn't realize that SL automically boots in 32 bit, even on the new iMacs. I have a core i5 with 8 gigs of RAM. Assuming I boot in 64 bit mode today, will my computer now utilize all 8 gigs? Was it only using 4 gigs in 32 bit mode?

Also, will some applications not run if I boot 64 bit? Any other info is greatly appreciated.
Click to expand...

Have done some research, the 32bit kernel can run 64bit applications (and does so by default), it can address up to 32Gb of RAM. The main reason for the 32bit by default is that a lot of existing kernel extensions (drivers etc. for applications such as Parallels and VMWare) are still only 32bit - you can't mix and match 32bit and 64bit kernel/extensions.

You can force a boot into 64bit by holding down 6 and 4 on the keyboard when the machine boots.
 
As a follow up to my previous post, here is a nice article explaining it in a little more depth.
 
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