I upgraded my Mac Mini to Snow Leopard and saw that SL runs with a 32 bit kernel. I've read two explanations: the BIOS is 32 bit in older Intel Macs (such as mine), and Apple does not let SL run with a 64 bit kernel on the more recent Mac Minis, for marketing reasons.

The newest Mac Mini can have 4 GB RAM. Can anyone tell me how much RAM is available to OS X in such a configuration?

By default Snow Leopard runs in compatibilty mode on all macs. To switch to Native mode boot holding the 6 and 4 key.

32-bit isn't the limiting factor in max ram on the older mac minis, it's the chipset.

64-bit doesn't help until you get above 4gb. So in theory the new mac minis will do 8gb or more with 64-bit...

Ed

So, on a new Mac Mini with 4GB of RAM and Snow Leopard running in 32-bit mode, how much RAM is reported?

Background information:

   1. All system hardware must have 64-bit drivers, including the CPU, chipset, and peripheral chips. The 64-bit kernel exclusively uses 64-bit kexts (drivers), and these are rarer than the 32-bit ones used by Leopard.
   2. It must use 64-bit EFI (firmware). Even though EFI32 can technically boot a 64-bit operating system just fine, Apple will not allow this. Only Macs made over the last few years include EFI64.
   3. Apple must allow the system to boot in 64-bit mode. This is the most confusing. Many Macs will not boot Snow Leopard in 64-bit mode even though they are brand new, have no unusual hardware, and include EFI64. This includes all non-Pro MacBooks and Mac Minis.

http://blog.fosketts.net/2009/08/30/64bit-snow-leopard-kernel/

Macs don't use BIOS, they use EFI - in 32 and now, 64-bit flavours, and the marketing angle is, I'm guessing, troll talk. Apple doesn't keep you from using 64-bit apps, even on a 32-bit kernel.

To run the 64-bit kernel, you require 64-bit processor (a Core2 Duo or better) and 64-bit EFI. Don't know if you have EFI64? Type this in the Terminal:

ioreg -l -p IODeviceTree | grep firmware-abi

The response tells you which EFI you have - 32 or 64-bit.

However, OS X SL still allows you to run 64-bit applications on a 32-bit kernel - a neat trick Windows can not do - as long as you have a 64-bit processor, and Apple's Universal Binary spec for app developers ensures that 64-bit apps can work in 32-bit compatibility mode - so nothing is really lost here for the "older" (pre-2008) Macs that don't have EFI64. Most of those machines cannot physically address more than 4 GB of RAM anyway - so it's a bit of a moot point. To answer your question - your mini would see 4 GB of RAM whether you used OS X 10.5 or 10.6, or Linux for that matter, but you cannot install 4 GB in an older Mini - sigh!

Happy Mac'ing!

Dan

ps: Re-reading your question - I think you were asking about the new minis? New minis would see 4 GB of RAM whether you booted in 32- or 64-bit mode.

Dan

Quote from: Dan Millar on November 14, 2009, 02:33:24 PM
ps: Re-reading your question - I think you were asking about the new minis? New minis would see 4 GB of RAM whether you booted in 32- or 64-bit mode.

Thanks, Dan. I had heard that Apple used a mapping technology to make all 4GB of RAM available to a 32 bit kernel, but I wanted to confirm it.