If it's 32 bit why can it address over 4 gigs of ram?

Kernel is the core of an OS, Mach_kernel is a universal binary file using ppc & i386(not x86 64) instructions... So can I say Leopard is not a real 64bit OS!

Intel specifics
While i386 support in XNU has existed since the mid-90s, and has been a shipping feature of OpenStep, the i386 part had not been used in Mac OS X until the advent of Intel machines in 2005/2006. And with the introduction of the 64 bit Mac Pro in 2006, x86_64 (AMD64, Intel64, EM64T, x64, ...) support has been added to XNU - but XNU is not a 64 bit kernel, though. XNU supports 64 bit user mode applications, but it is 32 bit itself. Since porting a 32 bit kernel to 64 bit is a big task, it could not be donein just half a year between the introduction of the first Intel machines in January of 2006 (until then, Apple developers had worked on finalizing the 32 bit i386 version) and the introduction of the Mac Pro in August.

There is just a single kernel image for 32 and 64 bit Intel: It is loaded as a 32 bit process in 32 bit protected mode on both kinds of machines, and if 64 bit support is detected, the kernel switches into long mode compatibility mode - a mode that supports running 32 bit code, but also allows easy switching to 64 bit code. So the whole kernel code is still unmodified 32 bit code, but tiny stubs that deal with copying between user address spaces (which can be 64 bit), and the syscall and trap handlers are 64 bit code. Next to being an easy port, this has the extra advantages that the 64 bit capable kernel can still easily support 32 bit KEXTs, and conserves memory by being able to use 32 bit pointers throughout a large part of kernel code. On the flip side, the kernel cannot use the extended x86_64 register set and is restricted to a 32 bit address space.

But while all other common 32 bit operating systems like Linux, Windows and the BSDs split the address space into 2 GB for user and 2 GB for kernel (2/2) or 3 GB for user and 1 GB for kernel (3/1), the i386/x86_64 version of XNU uses a 4/4 split: While the kernel is running, the user's data is not mapped into its address space, and while user code is running, the kernel is not mapped. So user and kernel can each have 4 GB of address space with the disadvantage of being less efficient in copying of data between user and kernel. But this way, kernel mode can map more devices into its address space (like video cards with a lot of memory), and manage more RAM, thus pushing out the limit when a true 64 bit kernel is required.

Shouldn't this whole thread be moved to the debates forum?

if (cpuid_extfeatures() & CPUID_EXTFEATURE_EM64T) {
kprintf("EM64T supported");
if (PE_parse_boot_arg("-legacy", &legacy_mode)) {
kprintf(" but legacy mode forced\n");
} else {
IA32e = TRUE;
kprintf(" and will be enabled\n");
}
}

Oh and since service pack1, vista 32bit has no problems with 4 gig or higher..

envying, i don't see anything that says that's it's not 64bit, really

what you posted simply enforces my statement, 64bit is threated as an extension, and it's enabled as soon as it's detected at boot, and the kernel runs everything @64bit.
this kind of approach disallow the addressing of the entire memory in a single space page, but you can open as many spaces as you like.
still, it doesn't mean there is a some kind of emulation whatsoever.
it is 64bit

As far As I know Mac os leopard is not Fully 64 bit....
But the 4 gig issue is not related to 32 bit or 64 bit... well from what I've read...
If you want to go higher than 64 gig you will need an 64 bit os...

Oh and since service pack1, vista 32bit has no problems with 4 gig or higher..

and thats not with any memory holes.... ETC!!!

Leopard is the Last Operating system to receive "Carbon" support. 10.6 will force everyone to move to 64 Bit Carbon.

As far As I know Mac os leopard is not Fully 64 bit....
But the 4 gig issue is not related to 32 bit or 64 bit... well from what I've read...
If you want to go higher than 64 gig you will need an 64 bit os...

Oh and since service pack1, vista 32bit has no problems with 4 gig or higher..

and thats not with any memory holes.... ETC!!!

leopard is 32bit, when snow leopard comes out, that's 64bit. 32bit os's can not address over 8gb's. 64bit os's will address up to 32gbs.

leopard is 32bit, when snow leopard comes out, that's 64bit. 32bit os's can not address over 8gb's. 64bit os's will address up to 32gbs.

64-bit snowlepers kernel works same as 32-bit, only difference - kernel itself can use more than 4gb (will we ever need that ?)

But correct me if I'm wrong. Snow leopard will support PPC as well, which wouldn't make it a true 64-bit OS?

As far As I know Mac os leopard is not Fully 64 bit....
But the 4 gig issue is not related to 32 bit or 64 bit... well from what I've read...
If you want to go higher than 64 gig you will need an 64 bit os...

Oh and since service pack1, vista 32bit has no problems with 4 gig or higher..

and thats not with any memory holes.... ETC!!!

So when are we going to notice this 64bit business? Ive never used more than 4gb of ram with one application addressing it all... are there sum magic instructions that are 64bit that willl significantly better the whole experience of using osx? or is this impressing us with bits and bytes?

I really doubt this will make a difference except for those with enormous ammounts of memory.

Leopard, on the other hand, can address far more. I currently have installed and running 8GB in my Leopard system, and it can fully access all of it. 8GB in a Windows XP/Vista 32-bit system will still only use 3.5GB.

I wish my Leopard install would be able to use all 8GB I have. I installed 8GB and it wouldn't boot all the way to the desktop...just blue screen with no icons or cursor. Removed a stick of DDR2 and it would boot to the desktop with 6GB installed. About this Mac only recognized 4GB, but System profiler identified all 3-sticks (6GB). Apps like console, software update and the installer app would launch and quickly crash. Removing another stick (4GB total) would give me a more stable system with all apps functioning as they should.

I guess it's an issue with AMD processors and 64-bit addressing under Leopard (or lack there of).

If it's 32 bit why can it address over 4 gigs of ram?

“Number four,” said Jobs. “Leopard is 64 bit from top to bottom.” This is the first time that 64-bit will be mainstream in the computer world, he said — not only does mean Leopard’s Unix underpinnings will be 64-bit, but so will Cocoa.

“One version of Leopard runs 32-bit and 64-bit apps side by side,” explained Jobs. “If you write a 64-bit app, you can guarantee that it will run on every copy of Leopard out there.”

To demonstrate the capability, Jobs loaded a giant photograph — 4GB in size — into a demo application that showed CPU and disk access. One version ran in 32-bit mode, the other in 64-bit mode. Running filters on both systems, the 32-bit version took 81 seconds to complete the tasks, hammering the hard disk in the process. The 64-bit version was able to load everything into memory, and finished in 28.48 seconds.

The Kernel is a true 32/64bit hybrid. This is excellent as the drivers from panther/jaguar days still work.Just run the included Chess program and fire up Activity Monitor and look for Chess. It will show up as Intel 64 bit if you have a 64 bit capable processor.

I know for sure that 32-bit Windows will NOT address (read "use") >3.x Gb. (It's somewhere about 3.2-3.5 Gb depending on how you measure it) From what I understand there has been a limit of 2Gb of addressed space being available to any single application, however that has been fixed through updates and service packs. Also the service packs have served to change how the memory is reported, so if you have 4gb installed, it will "recognize" it all, but it will not address (use) it all.


Note the "Physical memory available to Windows"

I understand my install of Leo is kinda jacked up as it's modified to run on my AMD, but it doesn't seem there should be much difficulty running the 64-bit code as AMD is the originator of the x86-64 instructions (for once, Intel had to adopt a standard they didn't create). Every item in my "Activity Monitor" shows it's kind as "Intel" (not "Intel 64") but completely recognizing all 4gb of memory. Does that mean my Leo is running the 64-bit extension to address it?


I tried that but it still showed up as just "Intel", not "Intel 64"

PAE does the memory job for 4GB. You are still 32bit world. AMD's AMD64 and Intel's EM64T are compatible with each other, but not the same 100%, this is with all CPU instruction sets. And your AMD lacks of SSSE3, witch is the main deal here between AMD and Intel 64bit way in Apple's mind.

Actually the chip in my Hack is an AMD Athlon X2 6000+. It's the 125w version and it does have the SSE3. (I linked to Wikipedia as it was quicker and easier than booting to Windows to grab a screenshot with CPU-Z)