The PowerPC G3

Processor: Taking

the Macintosh to

the Next Level

A little background

Nearly six years ago, Apple, IBM, and Motorola joined forces to create a new processor technology that would bring the performance advantages of the RISC (Reduced Instruction Set Computing) architecture—at that time limited to costly workstations—to personal computers. The result of this initiative was the development of PowerPC processor tech- nology, which Apple debuted in 1994 with the introduction of the Power Macintosh line.

The initial Power Macintosh models were based on the first implementation of the new chip technology: the PowerPC 601, which was intended for use in high-end personal computers. In early 1995, Apple introduced products based on the PowerPC processor technology’s second generation—the PowerPC 603, which utilized a chip design optimized for use in low-end to midrange desktop systems and portables. This was quickly followed by the introduction of the second-generation high-end PowerPC processor: the PowerPC

604.Since then, both IBM and Motorola have made enhancements to the PowerPC 603 and

604(now the 603e and 604e), and these enhanced chips have been used in subsequent Apple systems.

PowerPC Processor Roadmap

A roadmap for the development of PowerPC processor technology,

from its inception to the end of the century.

The PowerPC G3 performance story

The emergence of the PowerPC G3 processor marks the third phase in the development of this advanced processor technology. Touted by Microprocessor Report (February 17, 1997) as “an outstanding combination of high performance and low cost,” the PowerPC G3 builds on many of the features pioneered by the PowerPC 603 and 604. However, this innovative chip differs from the earlier implementations of PowerPC processor technology in several significant ways:

•The PowerPC G3 is the first processor specifically optimized for the Mac OS.

•It incorporates an innovative backside cache design that speeds access to level 2 cache.

•It contains large (32K) on-chip level 1 data and instruction caches, for a total of 64K level 1 cache.

•It’s produced using an industry-leading 0.25-micron manufac- turing process.

PowerPC G3 optimization features include the following:

•Addition of a second integer ALU (arithmetic and logic unit), which allows the processor to execute two successive integer operations in parallel

•The ability to fetch four instructions per cycle from the cache

•A “hardware tablewalk” feature, which allows the CPU to access virtual page tables directly

•Adoption of a dynamic prediction method for improving the efficiency of branch handling

These four innovations share one very important characteristic: the capacity to provide significant performance gains. Following is a more detailed breakdown of the advantages offered by each.

Mac OS optimization. Because the earlier PowerPC processor models were essen- tially developed simultaneously with Apple’s Power Macintosh line, there was no opportu- nity to optimize these chips’ performance for running Mac OS–based applications. But that was more than half a decade ago. Today, the Power Macintosh line is well established and Mac OS–based software abounds, placing the developers of the PowerPC G3 processor in the unique position of having the luxury to consider—and optimize—chip design in light of actual software performance.

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Apple G3 manual Next Level
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G3 specifications

The Apple G3, introduced in 1997, marked a significant leap in Apple's computer technology and design philosophy. This series of Macintosh computers was powered by the PowerPC G3 processor, which had a clock speed ranging from 233 MHz to 750 MHz, depending on the model. The G3 chip was notable for its advanced features, including a 32 KB L1 cache and the ability to support a more complex 256 KB L2 cache. This allowed the machines to execute instructions more efficiently than their predecessors, enhancing overall performance for various computing tasks.

One of the defining characteristics of the Apple G3 line was its innovative design, which combined form and function. The desktop models featured a sleek, curving case, famously known as the "Blue and White" G3, while the all-in-one iMac G3 showcased vibrant colors and an iconic translucent design that became a hallmark of Apple devices.

The Apple G3 was notable for its extensive use of USB ports, which was a relatively new technology at the time. This foresight helped pave the way for the adoption of USB peripherals, allowing users to connect a wide range of devices, from printers to scanners, with ease. Additionally, the G3 series also provided options for expansion via PCI slots, giving users the flexibility to upgrade their systems.

In terms of graphics, the G3 models were equipped with accelerators like the ATI Rage or the NVIDIA Riva TNT, providing improved visual performance for both professional applications and gaming. This was complemented by Apple's decision to support higher screen resolutions and better color depth, enhancing the multimedia experience.

Moreover, the Apple G3 introduced the Mac OS 8 operating system, which brought improved multitasking capabilities and a more streamlined user interface. This allowed users to experience a more intuitive and productive computing environment.

Overall, the Apple G3 line represented a critical evolution in Macintosh technology. It combined powerful processing, innovative design, and new technologies that set the stage for future developments in the Apple ecosystem. The G3 series not only solidified Apple’s presence in the computing market but also laid the foundation for the modern computing experience that would follow in the ensuing years.
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