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PowerPC G4 is a designation used by Apple Computer and Eyetech to describe a ''fourth generation'' of 32-bit PowerPC microprocessors. Apple has applied this name to various (though closely related) processor models from Freescale, a former part of Motorola. Motorola and Freescale's proper name of this family of processors is PowerPC 74xx. Macintosh computers such as the PowerBook G4 and iBook G4 laptops and the Power Mac G4 and Power Mac G4 Cube desktops all took their name from the processor. PowerPC G4 processors were also used in the eMac, first-generation Xserves, first-generation Mac Minis, and the iMac G4 before the introduction of the PowerPC 970. Apple completely phased out the G4 series for desktop models after it selected the 64-bit IBM-produced PowerPC 970 processor as the basis for its PowerPC G5 series. The last desktop model that used the G4 was the Mac Mini which now comes with an Intel processor. The last portable to use the G4 was the iBook G4 but was replaced by the Intel-based MacBook. The PowerBook G4 has been replaced by the Intel-based MacBook Pro. The PowerPC G4 processors are also popular in other computer systems, such as the AmigaOne series of computers and the Pegasos from Genesi. Besides desktop computers the PowerPC G4 is popular in embedded environments, like routers, telecom switches, imaging, media processing, avionics and military applications, where one can take advantage of the AltiVec and its SMP capabilities. ==PowerPC 7400== The PowerPC 7400 (code-named "Max") debuted in August 1999 and was the first processor to carry the "G4" moniker. The chip operates at speeds ranging from 350 to 500 MHz and contains 10.5 million transistors, manufactured using Motorola's 0.20 μm HiPerMOS6 process. The die measures 83 mm² and features copper interconnects. Motorola had promised Apple to deliver parts with speed up to 500 MHz, but yields proved too low initially. This forced Apple to take back the advertised 500 MHz models of PowerMac G4. The Power Mac series was downgraded abruptly from 400, 450, and 500 MHz processor speeds to 350, 400, and 450 MHz while problems with the chip were ironed out. The incident generated 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 7400 series line.〔(Motorola and IBM Reveal PowerPC Plans )〕 The 500 MHz model was reintroduced on February 16, 2000. === Design === Much of the 7400 design was done by Motorola in close co-operation with Apple and IBM. IBM, the third member of the AIM alliance, designed the chip together with Motorola in its Somerset design center, but chose not to manufacture it, because it did not see the need back then for the Vector Processing Unit. Ultimately, the G4 architecture design contained a 128-bit vector processing unit labelled AltiVec by Motorola while Apple marketing referred to it as the "Velocity Engine". The PowerPC 970 (G5) was the first IBM-manufactured CPU to implement VMX/AltiVec, for which IBM reused the old 7400 design they still had from the design they did with Motorola in Somerset. The Xenon CPU in the Xbox 360 also features VMX, with added proprietary extensions made especially for Microsoft. POWER6, introduced in 2007, is IBMs first "big iron" CPU to also implement VMX. With the AltiVec unit, the 7400 microprocessor can 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. Furthermore, the vector processing unit 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 to applications designed to take advantage of the AltiVec unit. Some examples are Adobe Photoshop which utilises the AltiVec unit for faster rendering of effects and transitions, and Apple's iLife suite which takes advantage of the unit for importing and converting files on the fly. Additionally, the 7400 has enhanced support for symmetric multiprocessing (SMP) thanks to an improved cache coherency protocol (MERSI) and a 64-bit floating point unit (FPU), derived in part from the 604 series. The 603 series had a 32-bit FPU, which took two clock cycles to accomplish 64-bit floating point arithmetic. The PowerPC G4 family supports two bus technologies, the older 60x bus which it shares with the PowerPC 600 and PowerPC 7xx families, and the more advanced MPX bus. Devices that utilize the 60x bus can be made compatible with either 6xx or 7xx processors, enabling a wide variety of offerings and a clear and cheap upgrade path while keeping compatibility issues at a minimum. There are primarily two companies manufacturing system controllers for 7xx and 7xxx computers, Tundra with their Tsi1xx controllers and Marvell with their Discovery controllers. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「PowerPC G4」の詳細全文を読む スポンサード リンク
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