Author Topic: The G5 and Mac OS X: Less 64-bit Than You’d Think (August 2014, Article)  (Read 1778 times)

Offline chrisNova777

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When Apple introduced the Power Mac G5 in June 2003, it made a big deal of the G5 being a 64-bit CPU. It even mentioned that on the box. But what does that mean to Mac users?

Power Mac G5
Power Mac G5

At first, not much. Mac OS X 10.2 Jaguar, which was current at that time, had almost no 64-bit support. About the only thing it could do was address more than 4 GB of RAM on dual-processor Power Macs, which support up to 8 GB.

OS X 10.3 Panther, released in October 2003, didn’t have much more, but the software could take advantage of the G5’s 64-bit address space, 64-bit registers, 64-bit integers, and hardware square root function.

It wasn’t until OS X 10.4 Tiger arrived in April 2005 that those 64-bit G5 Macs gained a bit of real 64-bit support. On a G5 Mac, any application could use 64-bit address space, thus accessing more than 4 GB of RAM.

Leopard Embraces 64 Bits – Sort Of
It was OS X 10.5 Leopard that took the PowerPC 970 (G5) as far as Apple ever would into the world of 64 bits – and the real beginnings of 64-bit support for Intel Core 2 Duo processors. In its review of Leopard, Ars Technica says, “The PowerPC instruction set was designed with a 64-bit implementation in mind” but 64-bit was a much more significant thing for Intel’s x86 architecture.

For the first time, the Mac OS had a full 64-bit GUI (Graphical User Interface). With Tiger, 64-bit apps couldn’t access the GUI at all. And best of all, the 32-bitness and 64-bitness were intermingled into a single operating system – and on top of that, Leopard was the only version of Mac OS X to support both PowerPC and Intel architecture from the same install disc, and both platforms could boot from a hard drive formatted using Apple Partition Map (APM) instead of GUID, which only supports Intel Macs. Quite a feat!

Unfortunately, the kernel itself remained 32-bit to maintain compatibility with existing drivers.

64-bit Software for the G5
None of this means much unless you have software designed to take advantage of the 64-bitness of the G5 CPU – and there wasn’t much. Researching online, here’s the list I’ve come up with:

AU Lab (a system-wide audio equalizer)
Apache web server
Image Capture
Quartz Composer
All of these came with OS X 10.5 Leopard. With only the Power Mac and iMac ever available with G5 CPUs, and with the iMac not supporting enough memory to justify using 64-bit operation, the software industry pretty much ignored 64-bit PowerPC support.

G5 Performance vs. Intel Core Duo
Modern benchmarking software such as Geekbench 3 no longer supports PowerPC systems, but Geekbench 2 did. Here are some results:

2.5 GHz Power Mac G5 Quad, 3738
2.7 GHz Power Mac G5 (Mid 2004), 2442
2.3 GHz Power Mac G5 Dual, 2312
2.5 GHz Power Mac G5 (Mid 2004), 2292
2.3 GHz Power Mac G5 (Mid 2004), 2103
2.0 GHz Power Mac G5 Dual, 2017
2.0 GHz Power Mac G5 (Mid 2004), 1863
1.8 GHz Power Mac G5 (Mid 2004), 1708
And here’s how it compares to early Intel Macs released in 1986:

2.0 GHz Core Duo Mac mini, 2565
1.83 GHz Core Duo Mac mini, 2477
1.66 GHz Core Duo Mac mini, 2270
1.5 GHz Core Solo Mac mini, 1529
That 1.83 GHz 2006 Mac mini has a higher Geekbench score than any G5 except for the Late 2005 Quad, while the 1.66 GHz Mac mini has a level of performance that falls between a dual processor 2.0 GHz and 2.3 GHz G5. And the 2.0 GHz Core 2 Duo Mac mini introduced in 2007 scores 2767 – almost 8% more powerful than the Core Duo at the same clock speed.

Most Late 2006 and all 2007 models had Core 2 Duo processors that could handily outperform a dual-processor or dual-core G5, giving developers even less reason to write software for a discontinued, dead-end platform.

That said, these are the most powerful PowerPC Macs ever made, and even if there isn’t much 64-bit anything for them, they are powerful performers in their own right.

I am writing this on one of those 2.0 GHz Core 2 Duo Mac minis from 2007, and sitting next to it is a 2.3 GHz dual-processor Power Mac G5 with just a slightly lower Geekbench 2 score. Although I don’t have as many browser options and it’s a lot noisier, it runs OS X 10.5 Leopard nicely and has 4 GB of RAM, more than this Mac mini supports. It’s my go-to machine for testing PowerPC software, and the drive also has an OS X 10.4 Tiger partition.

But despite having a 64-bit CPU, it pretty much works in 32-bit mode all the time.