PowerPC G4

The PowerPC G4 is a Microprocesseur 32 bits RISC manufactured by the company Motorola, in close cooperation with Apple. It is a PowerPC of second generation, presented as being of fourth generation by Apple. It is currently still manufactured by Freescale.

PowerPC G4 is primarily used in the Macintosh of Apple left between 1999 and 2005 like, in a more anecdotic way, in the Amiga new generation: the Amiga One and the Pegasos. It décine in several versions including 7400,7410,7450,7451,7445,7455,7457,7470,7447,7448 (most recent). One can also hear sometimes of G4Max, G4e, G4+, etc

It is first PowerPC to include a named vectorial calculating unit 128 bit AltiVec (Velocity Engine in the USA). These registers 128-bit are separated from the device of instructions 32 Bits just like more than 160 new instructions especially designed to treat arithmetic operations generally used in the handling of the three-dimensional charts, the image and the sound. Concretely, AltiVec is the more powerful competitor of the SE from Intel and the 3DNow! of AMD. Armed with its 160 instructions and 32 registers 128-bit, it proved to be a worthy candidate. It is obvious that to benefit from these new instructions, Apple was obliged to rewrite the software which fontionnaient until there under PowerPC G3. The software not-optimized for Altivec did not function more quickly with G 4 qu ' with G3. On the other hand the perfectly optimized software was incredibly swifter. G4, having branches of very short instructions, was extremely fast to reach quickly its instructions, it resulted from it from the really astonishing performances in certain cases of figure vis-a-vis processors given rhythm at quite higher speeds. Engraved mainly in 0,18 micron then into 0,13, G4 functions of 350 MHz with 1,8Ghz (even more with the last evolutions of Freescale) with a variable bus between 100 MHz and 166 MHz for the most recent versions. It is rather powerful while generating little heat. The first versions of G4 integrated 10,5 million transistors the most recent versions saw this number carried to 33 million. There exists still nowadays of such processors which preserve despite everything a positive ratio price quality

IBM refused to manufacture G4, because in its eyes it was primarily about improved G3, more than of a real successor of PowerPC 604 that G3 had certainly exceeded on the level of the power (especially because of a management of the memory hiding place optimized) but never really replaced. Although very powerful, G3 and G4 were seen more like successors of the 603 by IBM. IBM really did not believe in Altivec. The absence of IBM in the G4 adventure weighed heavy on the speed of evolution of this processor, IBM more quickly improving the processes of engraving than Motorola (during the life of G3, the processes of engraving on copper or technology ONESELF were conceived by IBM and not Motorola for example). Motorola was a long time unable to make exceed in G4 the 450 then 500 MHz, which penalized Apple heavily. However, pushed by Apple whose committed efforts to adapt the software to Altivec were important, IBM will decide later to integrate Altivec into the powerful processor 64 bits PowerPC G5.

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