Leopard To End The Power PC G3 Era - An Affectionate Look Back At 10 Years Of G3 Computing
Wednesday, October 10, 2007
by Charles W. Moore
Still no official release announcement, but Apple has three weeks yet to get OS 10.5 Leopard out the door in time to meet their promise of Leopard availability by the end of October. It’s been a long wait. OS 10.4 Tiger was released way back on April 29, 2005, which means that if the rumor mills are correct and Leopard leaps at the end of October, it will have been 30 months (2 1/2 years) between major Mac OS version upgrades.
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In my estimation, this has not been a bad thing. First, it allowed Apple to thoroughly debug OS 10.4 before moving on to the new System version. I found that the early release builds of Tiger had some rough edges, so to speak, although since about version 10.4.7, it has been a very smooth and dependable performer on my Macs. I’m anticipating that there will be one more Tiger “.4.xx” update to version 10.4.11, probably before the Leopard release, and it will become the definitive Tiger final version, as 10.3.9 has been for Panther and 10.2.8 for Jaguar.
OS 10.4.11 will also be the last Mac OS version to support G3 and early-model G4 iBooks and PowerBooks, at least officially. That will mean that all G3 and the Revision A 800 MHz 12” iBooks, all G3 PowerBooks, including Lombards and Pismos that have been upgraded to 433 MHz and 550 MHz G4 processors respectively, plus the 400 MHz, 500 MHz, 550 MHz, 667 MHz and 800 MHz G4 Titanium PowerBooks won’t make the cut, or to view it the other way, the minimum spec. Apple laptops that will be supported by Leopard are the 867 MHz TiBook and 12” Aluminum PowerBook, and the 933 MHz 14” iBook While Ryan Rempel’s XPostFacto may be updated to enable Leopard installs on unsupported hardware, IMHO the projected support cutoff threshold at the 867 MHz G4 processor is likely a sensible one. While I’m satisfied with the performance of OS 10.4 Tiger on my 700 MHz G3 iBook and two my 550 MHz G4 Pismo PowerBooks, at times they do labor a bit, and I don’t think I will try to push them any farther than OS 10.4.11 even if a Leopard install hack becomes available.
Those G3s and early G4s have had a great run on Mac computers, but there comes a tipping point in the life of virtually all technologies that they shift from being current (or reasonably current) to obsolete. For example, I can’t think of any automobiles, at least ones marketed in the developed world, that are still equipped with a carburetor. Electronic Fuel Injection has rendered carburetors obsolete, although my carburetor-equipped 1989 Toyota Corolla still runs great.
Some PC users still use floppy disks, and quite a few PC and Mac desktop users still have CRT displays, but both of those technologies are now widely considered obsolete. Apple hasn’t equipped any of its systems with floppy drives since 1998, and the last CRT Mac was the eMac that was discontinued last year.
When Apple switched to the IBM/Motorola Power PC CPU in 1994, even the mightiest of the foregoing Motorola 680x0 series microprocessors became old hat overnight, although the transition was handled with admirable elegance and smoothness. Actually, the PowerPC got a relatively slow start on Apple laptops, with the first PowerPC models - the PowerBook 5300 and the Duo 2400 despite their astronomical prices being lackluster performers that didn’t exactly eclipse the foregoing 68LC040 models they replaced. One of my offspring had a PowerBook 520 at the same time I was using a PowerBook 5300, and in some contexts the 25 MHz 68LC040 would run rings round the 100 MHz PowerPC 603e in the 5300, although the PPC came into its own when floating point calculations entered the picture.
The next such revolution was the introduction of the Power PC 750 family of CPUs, more familiarly known as “G3” in November, 1997, which made the most powerful of the previous generation 603 and 604 (desktop only) Power PC CPUs yesterday’s news.
I remember a couple of weeks after the G3s were rolled out, the publisher of a small local newspaper phoned to ask if I thought buying a leftover 604 Mac would be a good idea. I quickly persuaded her to go with one of the first-generation beige G3 desktops.
The G3 had a relatively long run, thanks to a series of revisions, and it certainly wasn’t rendered obsolete overnight when the next-generation G4 family of Power PC chips was introduced in the late summer of 1999, not quite two years after the G3’s debut. In fact, Apple continued selling G3-based systems right up until the G3 dual USB iBook was replaced by the G4 iBook in October, 2003. Many MAc-users are still getting great service from their G3 machines, including me with my 700 MHz G3 iBook, which as noted runs just fine on OS X 10.4 Tiger.
However, the sun will set on the G3 as a contemporary processor chip when OS X 10.5 Leopard is released, almost 10 years after the G3 first made its debut. If the scuttlebutt is correct, the minimum hardware specification for Leopard support will be:
• An Intel processor or a PowerPC G4 or G5 processor of at least 867 MHz
• A DVD drive
• Built-in FireWire
• At least 256 MB of RAM for a PowerPC based Mac and 512 MB for an Intel-based Mac ( Note: I wouldn’t want to use any Mac running even Tiger with anything less than 512 MB of RAM. My daughter’s 1.2 GHz G4 iBook is just pathetic running Tiger with 256 MB, although she has stubbornly procrastinated about upgrading. My guess is that 1 GB of RAM will be the real-world practical minimum memory configuration for Leopard unless you are really patient about watching spinning beach-balls)
• A built-in display or a display connected to an Apple-supplied video card supported by your computer
• At least 6 GB of disk space available, or 8 GB if you install the developer tools
Whatever, 10 years of OS support for the G3 is more than respectable, and even those last 900 MHz PPC 750 FX iBooks will be four years old when Leopard pounces. Try running Windows Vista on a 10 year old (or for that matter a five year old) PC. Good luck with that. It’s time to put the G3 (and those early G4s) out to pasture and move on. Or not. OS 10.4 Tiger will still be a kick-ass OS for years to come yet, and I intend to use my G4 upgraded Pismos for at least a couple of years to come yet.
In any event, I look on the G3 and G4 microprocessors fondly. Even the first-generation PowerPC 750 233 MHz chip in my old WallStreet PowerBook remains an amazingly capable performer, running Classic Mac OS 9.2.2, after nearly 10 years of service.
Taking a look back at the PowerPC G3’s illustrious decade, It really began with the formation of an alliance in 1991 between Apple Computer, IBM and Motorola to develop a new personal computer microprocessor based on IBM’s Reduced Instruction Set Computing (RISC) mainframe POWER architecture that could challenge Intel’s dominant X86 Complex Instruction Set Computing (CISC) CPU’s for market dominance, Apple’s first PowerPC based Macs in 1994 were powered by 66 MHz PPC 601 CPUs, The 603 and 604 Power PC variants followed over the next four years with increased clock speeds, eventually reaching 300 MHz with the 603e and 400 MHz for the 604ev, although the fastest 604 Apple ever used in a computer was 350 MHz in the 1997 Power Mac 9600/350.
The first generation PowerPC G3 CPU, officially known as the PowerPC 750, was the first PPC chip designed to run on a 66 MHz bus, and introduced to the public in the original beige Power Mac G3 and original “Kanga” PowerBook G3 desktops in November 1997. The “beige” G3 was initially offered in 233, 266, and 300 MHz versions, while the PowerBook G3 was essentially a PowerBook 3400c with a 250 MHz G3 motherboard and a 5 GB hard drive. Indeed, it is possible to upgrade a PowerBook 3400 to G3 power by grafting in a Kanga motherboard.
The G3 CPU was really the first PPC CPU that was optimized for use with PowerPC based personal computers. The earlier PowerPC 601, 603, and 604 RISC processors had been originally designed for compatibility with IBM’s mainframe POWER architecture. The PowerPC G3 was also the first processor specifically optimized for the Mac OS.
The PowerPC 740/750 design (codename Arthur) was conceived as an evolutionary replacement for the PowerPC 603e chip that was used in many Apple desktop and laptop computers in the mid-1990s.
The optimization efficiencies incorporated in those first 233 MHz G3s were so great that it could hold its own against a 300-350 MHz PPC 604e CPU, so Apple almost immediately discontinued the older CPU except in multiprocessor models (the G3 has limited dual processor support), and planned development of a successor to 604 was scrapped. The G3 750 both outperformed Intel’s contemporaneous Pentium IIs while drawing less power, and was smaller in size as well.
The PPC 750 sported two 32 KB level 1 caches, one for instructions, the other for data, but the real genius of the G3 processor was its support for a level 2 (L2) cache of 256 KB, 512 KB, or 1 MB running at an intermediate speed between the 66 MHz system bus and the CPU’s core frequency. The Level 2 cache of the 750 increased performance by approximately 30% in most situations. The original PPC 750 processor was offered in clock speeds up to 366 MHz. One of Apple’s less successful ideas was leaving the L2 cache out of the first revision entry level WallStreet PowerBook G3 model, which hobbled that machine’s performance substantially. Happily, four months later Apple released the Revision B “PDQ” WallStreets, including a base 233 MHz model with 512k of L2 cache, which is the version I own.
PowerPC 745/755
In 1998, Motorola upgraded the G3 chip, shrinking the die size to 51 mm2, which was facilitated by a new aluminum based fabrication at .22m. The PPC 745/755 microprocessor supported a 100 MHz system bus and reached clock speeds up to 600 MHz. The 755 was the last Motorola G3 processor, and was used in the 600 MHz iBook.
PowerPC 750CX
After the PPC 755, Motorola abandoned G3 architecture in favor of its G4 chip, but IBM continued G3 development, with its PowerPC 750CX (codename Sidewinder), which was released in 2000 and was the first G3 CPU to incorporate an on-chip L2 cache instead of a separate cache running at a fraction of the CPU’s full speed. This both enhanced performance and reduced power consumption and complexity. The fact that the the onboard cache was only 256k was mitigated somewhat by it running at full CPU speed. The 750CX was used in the last-iteration (Paris) clamshell iBooks, which were available with 366 MHz and 466 MHz clock speeds.
PowerPC 750CXe
IBM’s next upgrade of the G3 chip was the 750CXe (codename Anaconda), introduced in 2001 and featuring 256 KiB on-die L2 cache. Running at 400 MHz, the 750CXe drew less than four watts, and had had 20 million transistors including its L2 cache. Its die size was 43 mm2 facilitated by a 0.18 ?m copper process, and it also featured improved floating-point performance over the 750CX. The PPC 750CXe supported up to a 133 MHz system bus and reached clock speeds as high as 700 MHz. It was first used in the 500 and 600 MHz iMacs in February 2001, and also found its way into several models of the iBook.
PowerPC 750FX
The 750FX (code-named Sahara) debuted in 2002 and was available in clock speeds up to 900 MHz. The 750FX’s bus speed climbed to 166 MHz and the size of the on-die L2 cache was doubled to 512 KiB. There were also several improvements to the memory subsystem: an enhanced and faster (200 MHz) 60x bus controller, a wider L2 cache bus, the ability to lock parts of the L2 cache. The 750Fx was manufactured using a 0.13 m copper-based fabrication with Low-K dielectric and Silicon on insulator technology, incorporating 39 million transistors, a die size of 35 mm2 and consuming less than four watts at 800 MHz under typical loads. The 750Fx was the ultimate G3 microprocessor used in Apple computers, the last on being the 900 MHz iBook of 2003. My 700 MHz iBook has a 750FX processor, and it’s been a surprisingly capable performer, as I’ve noted above currently supporting OS X 10.4.9 Tiger very nicely.
PowerPC 750GX
The 750GX (code-named Gobi), rolled out in in 2004 was the latest and most powerful G3 processor from IBM, but it never was used in any Apple computers. The 750GX has a on-die L2 cache of 1 MiB, top frequency of 1.1 GHz, support bus speeds up to 200 MHz among other enhancements compared to 750FX.
Apple offered this summary of the G3’s advantages when it was first released in 1997:
The level 2 cache is the link between level 1 on-chip cache and main memory. By relocating the level 2 cache from the logic board to the processor card (hence the name “backside”), the CPU can access level 2 cache directly using a dedicated bus specifically designed for this purpose. This enables the more effective use of level 2 cache, because even relatively large amounts of data can be stored and accessed rapidly and efficiently.As processor speed increases, so does the performance value of the backside cache. This design significantly speeds access to the level 2 cache and dramatically increases the overall system performance.
Large level 1 (on-chip) data and instruction caches
Level 1 cache is a small amount of high speed memory built into the processor and in the PowerPC G3 this cache has been doubled from 32k to 64k. With 32k dedicated to instructions and 32k dedicated to data, the processor can store frequently requested data in the cache and access it more rapidly.
State-of-the-art manufacturing process technology
Finally, the 0.25-micron process used to produce the PowerPC G3 processors does more than merely boost performance; it also enables the creation of smaller, cooler processors with extremely low power requirements.
Backside Cache -- Unleashing Processor Performance
By far the biggest boost to performance that the PowerPC G3 offers can be credited to its incorporation of an approach to level 2 cache memory known as backside cache. This approach effectively bypasses limitations on the speed at which transactions between the processor and the level 2 cache can occur. Earlier PowerPC processors used the system bus to access both the level 2 cache memory and the main memory, which could result in conflicts. For example, under the previous approach, at processor clock speeds above 200 megahertz, the CPU would often stall as it waited for data to arrive from the level 2 cache. To prevent such slowdowns, the PowerPC G3 processor features a new dedicated bus that handles only the CPU/cache transactions. This bus can operate at higher speeds than the system bus -- speeds that relate incrementally to the clock speed of the processor. This enables the more effective use of level 2 cache, because even the relatively large amounts of data they can store can be accessed by the process or rapidly and efficiently. In fact, as clock speeds increase, so does the performance value offered by the backside cache design.
However, as revolutionary as it was, the G3 750 family of microprocessors had its shortcomings, particularly lack of multi-processor support and SIMD capabilities (although those were never issues for laptops) and a relatively weak floating point unit, which are reasons why Motorola decided to break away from G3 development and concentrate on its 74xx G4 range of Power PC processors. While this column is mainly about the G3, it is germane to briefly discuss differences between the G3 and G4 architecture.
Apple and IBM were involved in the PPC 7400’s design and engineering in close cooperation with Motorola at its Somerset design center, but IBM decided that a Vector Processing Unit wasn’t necessary. The biggest distinction of G4 architecture compared with G3 is said vector processing unit (called “AltiVec” by Motorola, with Apple referring to it as the “Velocity Engine”).
AltiVec enables the 7400 microprocessor to do four-way single precision (32-bit) floating point math, or 16-way 8-bit, 8-way 16-bit or four-way 32-bit integer math in a single cycle. The vector processing unit is also superscalar, and can do two vector operations at the same time.
Additionally, the 7400 has enhanced support for symmetric multiprocessing (SMP), and also supports two bus technologies, the 60x bus which it shares with the PowerPC G3, and the more advanced MPX bus.
So while the G4, especially in its higher clock speed versions (Daystar Engineering still offers G4 processor upgrades up to 2.0 GHz for Aluminum PowerBooks) is still a reasonably formidable and capable microprocessor, the G3 is definitely showing its age, and it’s there comes a time to put even a great technology out to pasture. I don’t think anyone should feel too hard done by when Apple drops support for the G3 from the Leopard OS release, and even if Leopard can be persuaded to install on G3 and early G4 hardware via third-party hacking, few G3-powered Macs will have really adequate video support to run Leopard satisfactorily anyway.
My plan is to continue running OS 10.4.11 (or whatever the final update of Tiger is) on my remaining G3 and 550 MHz G4 machines for as long as they’re capable of useful service. For example, they should remain useful platforms for running my flatbed and slide scanners for the foreseeable future, and I have a very nice Fastmac 8x SuperDrive expansion bay module for the Pismos. FastMac even offers a Blu-Ray drive upgrade for the Pismo. Not dead yet by a long shot!
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