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Most of the G4 design was done by Motorola in close cooperation with Apple. The name refers to the design being the "fourth generation" of PowerPC's from Motorola. IBM, the third member of the AIM alliance, chose not to participate in the design of the G4 in part owing to microprocessor design disagreements concerning a Vector Processing Unit on the chip. Ultimately, the G4 architecture design contained a 128-bit vector processing unit called AltiVec (also known as "Velocity Engine" in Apple's marketing literature).
With the AltiVec unit, the G4 microprocessor can do four-way single precision floating point math, or 16-way byte math in a single cycle. Furthermore, the vector processing unit on the G4 is superscalar, and can do two vector operations at the same time. Compared to Intel's x86 microprocessors at the time, this feature offered a substantial performance boost -- if the application was coded to take advantage of the AltiVec unit.
Additionally, Motorola designed the G4 with enhanced support for symmetric multiprocessingSymmetric multiprocessing SMP is a multiprocessor computing architecture where all processors can access, and are equally close to, all random access memory locations. SMP is the most common small computer multiprocessor architecture. However, SMP does no (SMP). The G3Codenamed "Arthur", the PowerPC G3 name comes from the third generation of PowerPC microprocessor. The G3 is a RISC-based microprocessor, belonging to the PowerPC family of processors. It was used in Apple Macintosh computers such as the PowerBook G3, the microprocessor line had some support for SMP, but computers using G3s in the SMP role took performance hits. By contrast, the G4 supports not only multi-processing, but also allows G4s used in SMP computers to pass data chip-to-chip in an extremely efficient manner.
Another big performance boost in the G4 microprocessor came from a 64-bit ALUALU redirects here. Alternative meaning: Alu sequence. An arithmetic and logical unit (ALU is one of the core components of all central processing units. It is capable of calculating the results of a wide variety of common computations. The most common av, derived in part from the 604 series ALU. The 603 and G3 series had 32-bit ALUs, which took two clock cycles to accomplish 64-bit floating pointComputer arithmetic A floating-point number is a digital representation for a number in a certain subset of the rational numbers, and is often used to approximate an arbitrary real number on a computer. In particular, it represents an integer or fixed-poi arithmetic.
The FPU in the G4 was also taken from the 604 CPU, because it was roughly 25% faster per clock than the FPU in the G3; originally, the G3 was intended to be a step down from Apple's 604ev (MACH IV) CPU, but when they realized how fast it was with the fast backside L2 SRAM cache, they decided to scrap the PPC604ev, and stick with the PPC750 (G3).
The first version of the G4 microprocessor line was called the MPC 7400. It debuted in late summer of 1999 at speeds ranging from 350 to 500 MHz. The chip contained 10.5 million transistors and was manufactured using Motorola's 0.20 μm HiPerMOS6 process. The chip dieAn integrated circuit (IC is a thin chip consisting of thousands or millions of interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. As of 2004, typical chips are of size 1 cm2 or smaller, but larger ones measured 83 mm2 and featured copper interconnects.
Motorola's inability in 1999 to obtain yields of the G4 line at Apple's desired clock speed caused Apple to do an abrupt about-face on sales of its Power Macintosh G4 tower series of computers. The PowerMac series was downgraded abruptly from 400, 450, and 500 MHz processor speeds, to 350, 400, and 450 MHz. The incident caused a rift in the Apple-Motorola relationship, and reportedly caused Apple to ask IBM for assistance to get the production yields up on the Motorola G4 line.
The 1999 problems foreshadowed difficulities Motorola and Apple faced in competing with Wintel-x86 system clock speed increases, and the "Megahertz Myth." It also perhaps ultimately caused Apple to release SMP versions of the Power Mac G4 series (with the ad campaign "Two brains are better than one") to make up for a perceived gap in performance between the Power Mac line, and competing x86-based systems running at higher microprocessor clock speeds.
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