osx, 32 bits, 64 bits, oh my!

situbu42

macrumors newbie
Original poster
May 21, 2013
3
0
hi,

i looked around for answers all over so please forgive me if these questions have been answered before.

Given that I have a mac xserve with efi32 and osx 10.6.8. of course it runs with a 32 bit kernel. the machine has a 64 bit processor and will run 64 bit apps.

  1. Can a 32bit app address more than 4gb of memory?
  2. Can a 64bit app address more than 4gb of memory?
  3. If I had efi64 in the machine and booted the 64 bit kernel,
    • Can you run 32 bit apps?
    • Are 32 bit apps a bad idea (based on what you know/experienced)?
    • could a 32 bit app address more than 4gb of memory?

Do any of the answers above change with 10.7 or 10.8?

also on the mac in question, in about this mac, software, some apps listed say intel 64 bit = yes. for those that do not, could they detect the 32 it kernel and run as 32 bit but run as 64 bits when there is a 64 bit kernel?

any links to back up the answers are appreciated (i have to show this to someone else).

thanks in advance.
 

maflynn

Moderator
Staff member
May 3, 2009
65,029
30,954
Boston
Can a 32bit app address more than 4gb of memory?
No

Can a 64bit app address more than 4gb of memory?
Yes

If I had efi64 in the machine and booted the 64 bit kernel,
Can you run 32 bit apps?
Yes you should

Are 32 bit apps a bad idea (based on what you know/experienced)?
No, just limited to 32 bit address space. Some of my best friends are 32 bits :p

could a 32 bit app address more than 4gb of memory?
No, see my first answer. Since the memory structures within the app are 32 bit it is limited to only 4gb of ram.

Do any of the answers above change with 10.7 or 10.8?
I don't believe so, 32bit apps AFAIK still work on Lion

also on the mac in question, in about this mac, software, some apps listed say intel 64 bit = yes. for those that do not, could they detect the 32 it kernel and run as 32 bit but run as 64 bits when there is a 64 bit kernel?
I'm not sure, I'd hazard a guess some will and perhaps some won't.
 
Last edited:

Bear

macrumors G3
Jul 23, 2002
8,089
4
Sol III - Terra
...
  1. Can a 32bit app address more than 4gb of memory?
  2. Can a 64bit app address more than 4gb of memory?
  3. If I had efi64 in the machine and booted the 64 bit kernel,
    • Can you run 32 bit apps?
    • Are 32 bit apps a bad idea (based on what you know/experienced)?
    • could a 32 bit app address more than 4gb of memory?

Do any of the answers above change with 10.7 or 10.8?

also on the mac in question, in about this mac, software, some apps listed say intel 64 bit = yes. for those that do not, could they detect the 32 it kernel and run as 32 bit but run as 64 bits when there is a 64 bit kernel?
...
In short:
  1. No
  2. Yes
  3. -->
    • Yes
    • No
    • No

No changes with 10.7 and 10.8 I also doubt this will change with 10.9.

If it does not say "Yes" in the 64-Bit column, they are 32 bit only applications and can not run as 64 bit. It would require an update to the application that has 64 code included.
 

talmy

macrumors 601
Oct 26, 2009
4,705
266
Oregon
Can a 32bit app address more than 4gb of memory?
No. 2^32 = 4G so that's all it can address.
Can a 64bit app address more than 4gb of memory?
Yes.
If I had efi64 in the machine and booted the 64 bit kernel,
Can you run 32 bit apps?
Yes
Are 32 bit apps a bad idea (based on what you know/experienced)?
No. 64 bit apps are potentially faster because the architecture is better, but 32 bit apps run just fine.
could a 32 bit app address more than 4gb of memory?
No.

Do any of the answers above change with 10.7 or 10.8?
No, except they don't support a 32 bit kernel.

also on the mac in question, in about this mac, software, some apps listed say intel 64 bit = yes. for those that do not, could they detect the 32 it kernel and run as 32 bit but run as 64 bits when there is a 64 bit kernel?
The code is completely different, however the binary file can contain multiple executables, such as both 32-bit and 64-bit intel.

any links to back up the answers are appreciated (i have to show this to someone else).

thanks in advance.
Check anandtech.com -- they've run many articles in the past on the 64-bit OS X. versus 32-bit.
 

situbu42

macrumors newbie
Original poster
May 21, 2013
3
0
thanks all.

the machine in question is has MAMP and in about this mac, software, it is listed as intel 64 bit = yes.

does this mean that the mysql executable is a 64 bit process? how can i check the 64bitness of an individual process?

thanks again for the fast response.

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Some of my best friends are 32 bits :p
famous last words of a 32 bit app hater. :)