is OSX 10.5 Leopard 64bit or 32bit?

[chrisNova777]

Since Leopard is 32-bit it can address up to 4 GBs per processor.

For Core 2 Duo machines the maximum is, therefore, 8 GBs.

For 4-core machines it's 16 GBs,
and for 8-core machines it's 32 GBs.

Of course SL is 64-bit so the maximum is much greater.

But from a purely practical point of view the limit is determined by the largest compatible RAM module and the number of RAM slots in the machine. The 8-core Mac Pros have 8 slots. The largest compatible module is currently 4 GBs, so those machines can install up to 32 GBs.

https://discussions.apple.com/thread/2368815

not sure i agree with the rational behind this answer 100% because my g5 only had one processor and it had a max ram of 8gb with 8 slots of DDR1 and it comes from 2003, not 2007.

The short answer is that Leopard is a mix of 32-bit and 64-bit.

    Tiger added 64-bit support for low-level system libraries, enabling 64-bit for non-GUI applications.
    Leopard added 64-bit support throughout the system frameworks, so any app can be 64-bit.
    Snow Leopard will add a 64-bit kernel and many 64-bit user applications shipped by Apple. The 32-bit versions of all the frameworks and libraries are of course still available, but running apps in both modes requires both stacks to be loaded, which is inefficient, and a big reason why Apple is strongly encouraging developers to get on the boat and build their apps with a 64-bit version.

so the true answer is that leopard was part of a transitional phase over many iterations of versions of OSX
that began with TIGER and transitioned to supporting 64bit 100% in LION. and completed with 32bit support being fully deprecated  + removed in CATALINA

[chrisNova777]

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.