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PowerPC G4

PowerPC G4 is a designation formerly used by Apple 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 internal 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 microprocessors 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. The last portable to use the G4 was the iBook G4, which was replaced by the Intel-based MacBook. The PowerBook G4 was replaced by the Intel-based MacBook Pro.

The PowerPC G4 microprocessors were also popular in other computer systems, such as the AmigaOne series of computers and the Pegasos from Genesi. Besides desktop computers the PowerPC G4 was popular in embedded environments, like routers, telecom switches, imaging, media processing, avionics and military applications, where one can take full advantage of the AltiVec technology and its SMP capabilities.

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 Power Mac 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. The 500 MHz model was reintroduced on February 16, 2000.

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 IBM's first "big iron" CPU to also implement VMX.

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