Snow Leopard 32- vs 64-bit kernel, how to boot it, supported hardware

[gnasher729]

64-bit apps allow access to more RAM, more than 2GB. 64-bit kernel allows access to more than 64GB of RAM.

Strange, but Mac OS X doesn't seem to have an API to allow a 32-bit program to access greater than 2GB RAM, like Windows does?

1. You are confusing "address space" with "RAM". If you run a dozen 32 bit applications on a machine with 16 GB, they can use all the RAM with no problem, just each can't use more than 4 GB.

2. The limit in address space for 32-bit applications isn't 2 GB, it is somewhere around 3.5 GB.

3. A single MacOS X 32 bit application can use more than 4 GB of RAM through the well-documented memory-mapping APIs.

 

[Amdahl]

1. You are confusing "address space" with "RAM". If you run a dozen 32 bit applications on a machine with 16 GB, they can use all the RAM with no problem, just each can't use more than 4 GB.

Yes, I know. I may have been confusing, but I wasn't confused myself.

2. The limit in address space for 32-bit applications isn't 2 GB, it is somewhere around 3.5 GB.

Are you sure? All I could find in the docs is that 2GB is the largest allocation that can be requested.

3. A single MacOS X 32 bit application can use more than 4 GB of RAM through the well-documented memory-mapping APIs.

Well documented? Certainly not well referenced. I tried to find the answer to that exact question and came up with nothing in the docs. What is the API that allows this access?

 

[eldy]

SMS no longer works for my MacBook Pro 5,1 with 10.6.3. It's always booting into 32 bit mode unless I hold down the 6 and 4 keys at boot.

Is there a new way or setting to make booting into 64 bit mode automatic again?