64 bit vs. 32 bit in Tiger

[Viro]

The G5 can run in 32 bit mode as well. That's why it's running Panther alright. Tiger will have some bits that are written to take advantage of the 64 bits addressing the G5 provides.

[HomunQlus]

- G5 is a 64-bit processor - there is no 32-bit G5: More info
- Tiger will be the first operating system of Apple that can fully avail of the features provided by a 64-bit processor
- You can not run 64-bit operations on a 32-bit processor like G4
- As far as I know Tiger will be able to support more virtual memory on 64-bit systems and therefore making the system faster

[Zammy-Sam]

HomunQlus,
the G5 processor also supports 32bit as Viro mentioned. Following your link I read this line

Originally Posted by http://images.apple.com/powermac/pdf/PowerMacG5_TO_20041019.pdf

On other platforms, switching to a 64-bit computer requires migrating to a 64-bit operating system (and purchasing 64-bit applications) or running a 32-bit operating system in a slow emulation mode.With the PowerPC G5, the transition to 64-bit performance is seamless: Current 32-bit code—such as existing Mac OS X and Classic applications—runs natively at processor speed, with no interruptions to your workflow and no required additional investments in software. Unlike competing technologies, the PowerPC architecture was designed from the beginning to run both 32-bit and 64-bit application code.This enables the G5 processor to run Mac OS X natively for an immediate performance boost. In addition, more and more of the most popular applications, including Mac OS X itself, have been optimized for the PowerPC G5, so performance gains are even greater.

[HomunQlus]

Alright... didn't know that... thanks!

[Viro]

I should make myself more clear next time . Nowhere did I say the G5 wasn't 64 bit, but that it could run in 32 bit mode. Which of course implies that it isn't 32 bit, but doing some funky jazz to run 32 bit apps.

Ah well...

[RacerX]

You should remember where the G5 (PowerPC 970) is coming from. It was originally designed as a bridge from the PowerPC 604e/POWER3 processors (which are 32-bit) to the POWER4/POWER5 (which are 64-bit). IBM was finding that their clients were staying with the 32-bit systems due to software and the PowerPC 970 was going to give them a step up to the 64-bit world without having to leave their 32-bit software right away (thanks to it hybrid nature).

IBM added Altivec to get Apple to move to the processor. Apple had invested heavily in Altivec enhanced processes (as had many Mac developers). Altivec was originally a Motorola technology which IBM didn't want to get involved with.



A lot of this stuff depends on a combination of hardware and software. My SGI Indy uses a 64-bit processor and is running a 64-bit operating system, but still runs all my 32-bit apps (like Photoshop, Illustrator, GIMP and Acrobat Reader) seamlessly. Infact, when I first got it I didn't have a 64-bit operating system to run on it (IRIX 6.2) so I was running a 32-bit version (IRIX 5.3) instead. And it still ran great.

[Krevinek]

Originally Posted by Viro

I should make myself more clear next time . Nowhere did I say the G5 wasn't 64 bit, but that it could run in 32 bit mode. Which of course implies that it isn't 32 bit, but doing some funky jazz to run 32 bit apps.

Close, but not quite. The PPC is designed with expandibility in mind, much like MIPS. Chips like the G3/G4 can load data from RAM not just as 32-bits, but as 8/16-bit chunks too (doing the needed work to make it fill the 32-bit register correctly). This applies to storing data to RAM as well. What this means is that when the 970 was designed, it used an expanded spec for the PPC where the registers are 64-bit, but it can still load all the smaller data sizes as well. There is no funky jazz to run 32-bit apps, simply because 32-bit apps are native to begin with: no mode switch, no trickery, no special treatment. 32-bit apps just aren't aware of the new instructions to manipulate data in chunks larger than 32-bits (much like code that doesn't use Altivec is still native code on the G4).

[Viro]

That's cool then. Learn something new every day .