The G5 and Mac OS X: Less 64-bit Than You’d Think

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
  • Chess
  • Image Capture
  • MySQL
  • Quartz Composer
  • Xcode

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.

Keywords: #osxleopard #powerpc970 #powermacg5 #64bitness

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3 thoughts on “The G5 and Mac OS X: Less 64-bit Than You’d Think

  1. Ars Technica was wrong. OS X 10.4 was the first to officially support both PowerPC and Intel. Unofficially, Apple has been building x86 versions of it’s operating system for internal use almost from the beginning.

    • I don’t understand your comment. There were two separate versions of OS X 10.4 Tiger – one exclusively for PowerPC with a little bit of 64-bit support, and one for x86, which was 32-bit only initially, since that’s all Core Duo chips support. What exactly did Ars Technica get wrong?

  2. I would not consider 64-bit support as something very important in PPC-OS X. While more and more software updates demand a 64-bit OS on the Intel side, there are very, very few updates on the PPC side anyway. Fast PPC-Macs are still quite useful today as are early Intel-Macs (typing this on a 2006 MacBook, 32-bit core duo, for performance reasons under Mac OS 10.5.8). However there is something different to notice. All PPC-Macs in this performance class are using multiple times more electrical power. My MacBook consumes typically 20 to 40 Watts, a PowerMac G5, I guess, something like 5 or more times as much. Running such a machine most of the day during, let’s say, 200+ work-days a year, costs you real money.

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