Editing PowerPC G4 (section)

==PowerPC 7400==<!-- This section is linked from [[List of Macintosh models grouped by CPU type]] -->
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 [[Megahertz|MHz]] and contains 10.5 million transistors, manufactured using Motorola's 0.20 μm HiPerMOS6 process. The [[Die (integrated circuit)|die]] measures 83&nbsp;mm<sup>2</sup> and features [[Copper-based chips|copper interconnects]].

Motorola had promised Apple to deliver parts with speed up to 500&nbsp;MHz, but [[Fabrication (semiconductor)#Device test|yields]] proved too low initially. This forced Apple to take back the advertised 500&nbsp;MHz models of [[Power Mac G4]]. The Power Mac series was downgraded abruptly from 400, 450, and 500&nbsp;MHz processor speeds to 350, 400, and 450&nbsp;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.<ref>{{Cite web|url=https://www.macworld.com/article/158184/motorola-7.html|title=Motorola and IBM Reveal PowerPC Plans}}</ref> The 500&nbsp;MHz model was reintroduced on February 16, 2000.

=== Design ===
Much of the 7400 design was done by Motorola in close co-operation with [[Apple Inc.|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 [[AltiVec|VMX/AltiVec]], for which IBM reused the old 7400 design they still had from the design they did with Motorola in Somerset. The [[Xenon (processor)|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 (computing)|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 protocol|MERSI]]) and a 64-bit [[floating point unit]] (FPU), derived in part from the [[PowerPC 600#PowerPC 604|604 series]]. The [[PowerPC 600#PowerPC 603|603 series]] had a 32-bit FPU, which took two [[clock cycle]]s to accomplish 64-bit [[floating point]] arithmetic.

The PowerPC G4 family supports two bus technologies, the older [[PowerPC 600#60x bus|60x bus]] which it shares with the [[PowerPC 600]] and [[PowerPC 7xx]] families, and the notably 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 Semiconductor|Tundra]] with their Tsi1xx controllers and [[Marvell Technology Group|Marvell]] with their Discovery controllers.