Low End Mac's Online Tech Journal

The PowerPC G3 Story: From 233 MHz to 1.1 GHz

Dan Knight - 2007.05.24

The PowerPC G3 CPU was a big step forward in design. Where the earlier PowerPC 601, 603, and 604 RISC processors had been designed for compatibility with IBM's POWER architecture, the third generation (hence G3) processor was optimized for the code being run on PowerPC computers.

A 233 MHz G3 was so efficient that it could hold its own against a 300-350 MHz PPC 604e CPU, so Apple quickly moved away from the older CPU except in multiprocessor models (the G3 has very limited dual processor support).

The G3 is officially known as the PowerPC 750 family. This article provides an overview of that processor family as used in Apple computers.

PowerPC 750

The first generation G3, the PowerPC 750, was the first PowerPC CPU designed to run on a 66 MHz bus. It found its way into the original Power Mac G3, released in November 1997. The "beige" G3 was initially offered in 233, 266, and 300 MHz versions. (It was also the first Power Mac to use an IDE bus for hard drives.)

The PPC 750 had two 32 KB level 1 (L1) caches, one for instructions, the other for data. An external level 2 (L2) cache of 256 KB, 512 KB, or 1 MB was supported running at an intermediate speed between the 66 MHz system bus and the CPU's core frequency. The PPC 750 reached speeds as high as 366 MHz, and the faster chips made their way into a later, relatively rare 333 MHz and 366 MHz revision of the beige G3.

The beige Power Macs and original iMac had a 512 KB L2 cache running at half the speed of the CPU. The first PowerBook G3 (essentially a PowerBook 3400 with a G3 transplant) ran at 250 MHz, had a 50 MHz system bus, and a 512 KB L2 cache running at 100 MHz (a 5:2 ratio).

PowerPC 755

Motorola moved to aluminum fabrication and a tighter .22 µm die to produce the PPC 755 in 1998. The new CPU supported a 100 MHz system bus and achieved speeds as high as 600 MHz. The 755 was used in early iBooks.

After this, Motorola essentially abandoned the G3 in favor of the G4 (PowerPC 7400) architecture.

PowerPC 750CX

IBM kept developing the G3, and the PPC 750CX was the first G3 CPU to incorporate an on-chip L2 cache. This eliminated the need to have a separate cache running at a fraction of the CPU's full speed. Although the onboard cache was only 256 KB in size, the fact that it ran at full CPU speed made the 750CX a better choice than Motorola's 755.

The 750CX was first used in the second-generation iBooks, which ran at 366 MHz and 466 MHz.

PowerPC 750CXe

IBM introduced an enhanced version of the 750CX in 2001. The PPC 750CXe supported a 133 MHz system bus and reached speeds as high as 700 MHz. The 750CXe replaced the 750 starting with 500 and 600 MHz iMacs in February 2001.

IBM also improved floating point performance with this revision of the G3 CPU.

PowerPC 750FX

The next step forward came in 2002 when the PPC 750FX was designed to run on a 166 MHz system bus and at speeds up to 900 MHz. IBM doubled the size of the L2 cache to 512 KB, further improving the G3's efficiency. This was the last G3 revision used in Apple computers, possibly as early as the iBook 600.

PowerPC 750GX

Introduced in 2004, the PPC 750GX was IBM's last revision of the G3 design. The new version has a 1 MB L2 cache, could run on a 200 MHz bus, and topped out at 1.1 GHz. This CPU made its way into at least on upgrade for the blue & white G3, although Apple never used it.

Optimized Software Builds Bring Out the Best in Your Mac, 2009.06.30. Applications compiled for your Mac's CPU can load more quickly and run faster than ones compiled for universal use.
Low End Mac's Safe Sleep FAQ, 2009.06.15. What is Safe Sleep mode? Which Macs support it? How can you enable or disable it? And more.
The Original Macintosh, 2009.01.12. An in-depth look at the original Macintosh and how it shaped future Macs.
More in the Online Tech Journal index.

Links for the Day

Mac of the Day: Mac IIci, introduced 1989.09.20. The fastest Mac to date, the 25 MHz IIci was a real workhorse and a big hit.
February 12 in LEM history: 99: $4,320 for a 'free' iMac - 01: 10 Commandments of Macintosh - High-end word processing for free - 02: 8 OS X gotchas - Working less with my Mac than with my PC - Microsoft Office v. X - 03: New Zealand's Mac mag - 04: Nothing else is a Mac - 07: On Mighty Toaster Wings - Jobs stirs up DRM hornet's nest - OS X 10.2 best for Classic? - 08: Too much software choice is not a blessing - A month with Windows
Support Low End Mac

Recent Content on Low End Mac

Fix Home Button Delay, Tablet the Ultimate Mobile PC, iPad Notebook a Possibility, and More, iOS News Review, 2012.02.10. Also using your iPad at work, two photo editors, a new iPad text editor, Macally's magnetic iPad 2 stand, and more.
White MacBook Goes End-of-Life, Logitech Touch Mouse Supports Gestures, Firmware Updates, and More, The 'Book Review, 2012.02.10. Also MacBook Air better than any Ultrabook, docks for MacBook Pro models, Intel offers improved SSDs, and more.
Mac and iOS Browsers: Options Galore, Freeware Forum, 2012.02.10. Safari is adequate on Mac and great on iOS, but the range of good alternatives is stunning. LEM writers share their favorites.
Apple's Support Lead Shipping, Smartphones Outsell PCs, OS X Ported to ARM by Intern, and More, Mac News Review, 2012.02.10. Also the power of Tex-Edit Plus, Google and Twitter are already censoring the Web, Snow Leopard Security Update, and more.
LogMeIn: Remote Screen Sharing for the Rest of Us, Alan Zisman, Zis Mac, 2012.02.09. Configuring the Mac's built-in screen sharing to work over the Internet can be difficult or impossible. LogMeIn makes it easy.
15 Years Ago Motorola Unveiled the PowerPC G3, Low End Mac Round Table, 2012.02.06. The G3 processor was optimized for real world Mac software and made a big leap forward in efficiency.
Don't Kill Caps Lock, Learning to Love the iOS Keyboard, and an Adaptive iPad Keyboard, Charles W. Moore, Miscellaneous Ramblings, 2012.02.06. The Caps Lock key has a useful function, the iPad's keyboard really is useful, and checking out an adaptive keyboard for the iPad.
More links in our archive.

Recent Deals

About LEM Support Usage Privacy Contact

Low End Mac is an independent publication and has not been authorized, sponsored, or otherwise approved by Apple Inc. Entire Low End Mac website copyright ©1997-2012 by Cobweb Publishing, Inc. unless otherwise noted. All rights reserved. Apple, the Apple logo, Macintosh, iPad iPhone, iMac, iPod, MacBook, MagSafe, Mac Pro, Apple TV, and AirPort are registered trademarks of Apple Inc. Additional company and product names may be trademarks or registered trademarks and are hereby acknowledged.
Advice is presented in good faith, but what works for one may not work for all. Please report errors to .
LINKS: We allow and encourage links to any public page as long as the linked page does not appear within a frame that prevents bookmarking it.
Email may be published at our discretion unless marked "not for publication"; email addresses will not be published without permission, and we will encrypt them in hopes of avoiding spammers. Letters may be edited for length, context, and to match house style.
PRIVACY: We don't collect personal information unless you explicitly provide it. For more details, see our Terms of Use.

Custom Search

Follow Low End Mac on Twitter
Join Low End Mac on Facebook

Low End Mac Reader Specials

TypeStyler 11 is now in the Mac App Store!! -- Special Introductory Price of $59.95!! -- To Buy From The Mac App Store Click Here Now!! Or buy direct from Strider Software.

Don't install Parallels to play poker online! Poker Mac will show you how to download and install a native Mac poker and Mac Casino applications in minutes.

Affiliates

Amazon.com
The Apple Store
The iTunes Store
PC Connection Express
GainSaver
Parallels Desktop for Mac
eBay