Drummerboy said:
Attempting to put two and two together:
I keep hearing the Merom and Conroe referred to as processors with 64-bit extensions.
Are these extensions similar to the MMX extensions of long ago?
The case with MMX was that you could still use new software that was coming out. The software would check if you had MMX and would inturn use the optimized MMX code (no MMX caused lower quality graphics for games).
Does this mean that the OS's will remain compatible with the 32-bit Core?
If yes, does that mean that software only needs to be retooled if it wants to take advantage of the 64-bit extentions?
So in turn does that mean that based on current information software for at while should still run on the Core Duo & Solo hardware, just that it won't be as accelerated as it could be?
Edit:
If the "EM64T" extension turns out to be similar to "MMX" extensions then its not a full-architecture change requiring full OS and software changes and is no different than any other speed increase Intel does. Therefore waiting for this is no different than waiting to buy a computer because a faster processor will be coming soon.
No, it it more like the move from 16-bit to 32-bit with the introduction of the 386. Whereas MMX was something that an individual process could choose to use or not, EM64T/AMD64 is different. It is a new operating mode of the processor. It is possible to force the processor to switch between 32-bit and 64-bit mode, but you get a MAJOR performance hit. It is significantly better to run the processor in 64-bit mode the whole time. That is why on Windows, you need a whole new version of Windows (Windows XP Professional x64 Edition) to run in 64-bit mode.
MMX is a set of extra instructions. (Same with SSE, SSE2, SSE3, and AltiVec.) A program just tries to send the new instructions to the processor, and if the processor understands it, it uses it. If not, then the processor sends an error. x86's 64-bit mode is one where the processor needs to be put into '64-bit mode', then you send 64-bit data to it, and execute 64-bit instructions. If you want to run 32-bit processes, you need to take the entire processor out of 64-bit mode to run 32-bit processes. Because in a modern multithreaded OS, it isn't feasable to kill all 64-bit processes every time you want to run a 32-bit one, Microsoft gets around this by basically emulating the 32-bit mode INSIDE the 64-bit mode. (Vaguely similar in theory to Rosetta, but without the performance hit, since it is just 'padding' the 32-bit data into 64-bit data, and passing the 32-bit instructions through to their 64-bit counterparts.)
Yes, early on, Intel denegrated AMD's 64-bit extensions by attempting to put x64 on par with MMX as 'just an extension'. But in reality, it is basically a new architecture that happens to have the same instruction set as x86, only supporting 64-bit. Just as adding 32-bit to the 386 was essentially a new 32-bit archtiecture, rather than 'just an extension' of the 16-bit 286.
This is different than 64-bit on PowerPC, where you don't need to shift the processor into a different mode, you just have to have an OS that recognizes the 64-bit-ness, and allows applications to access the larger address space, and work on 64-bit chunks of data.
What this means is that OS X 10.4.5 for Intel will theoretically work on the new 64-bit Intel Macs (of course, Apple always blocks using an older OS on a newer model, but in theory it would work,) but it would only operate in 32-bit mode. Likewise, if Apple were to compile OS X 10.4.8 (for example,) for 64-bit Intel when Conroe comes out, and NOT for 32-bit Intel, it wouldn't boot at all on the current iMac, MacBook Pro, or mini.
That means that if Apple does release a 64-bit version of OS X Intel, they will have THREE code branches to maintain... PPC, 32-bit Intel, and 64-bit Intel. (PPC, wether 64-bit or 32-bit, isn't that much different to require a completely separate code base. x86 is different enough.) That could mean three 10.5 install discs, one for 32-bit Intel, one for PPC, and one for 64-bit Intel.
Drummerboy said:
Does anyone have any thoughts on my post #125 of this thread in regards to EM64T being similar to MMX?
Hopefully this answers it for you. :-D
And yes, RollTide, 32-bit apps will be around for a while. Either that, or Apple will have to offer everyone who bought an iMac, MBP, or mini an exchange for a new 64-bit equivalent later this year.