PowerPC 7400

PowerPC G3

PowerPC G3 is a designation used by Apple Computer to a third generation of PowerPC microprocessors from the PowerPC 750 family designed and manufactured by IBM and Motorola/Freescale. The term is often, incorrectly, imagined to be a physical model of processor when in fact a number of processors from different vendors have been used.

The G3 is a RISC-based microprocessor, belonging to the PowerPC family of processors. Such designations were applied to Apple Macintosh computers such as the PowerBook G3, the multicolored iMacs, iBooks and several desktops, including both the Beige and Blue and White Power Macintosh G3s. The low power requirements and small size made the processors ideal for laptops and the name lived out its last days at Apple in the iBook. The 750 family processors is widely used in embedded devices like printers and storage devices, spacecraft and game consoles from Nintendo, and is also used in other PowerPC based computers, like newer Amigas and Pegasos.

The 750 family had its shortcomings, namely lack of SMP support and SIMD capabilities and a relatively weak FPU. Motorola's 74xx range of processors picked up where the G3 left off.

Processors

PowerPC 740/750

The PowerPC 740/750 design (codename Arthur) was introduced in late 1997 as an evolutionary replacement for the PowerPC 603e. Enhancements included faster 60x system bus (66 MHz), larger L1 caches (32 KiB instruction and 32 KiB data), enhanced integer and floating point units and higher core frequency. The 750 model also included an option of 256, 512 or 1024 KiB external L2 cache.

The 740/750 models had 6.35 million transistors and was initially manufactured by IBM and Motorola in an aluminium based fabrication process. The die measured 67 mm² at 0.26 μm and it reached speeds of up to 366 MHz while consuming 7.3 W. In 1999, IBM used a copper based process at .20 μm which increased the frequency up to 500 MHz and decreased power consumption to 6 W and the die size to 40 mm².

The PPC 740 slightly outperformed Pentium IIs while consuming far less power, and were smaller in size. The off-die L2 cache of the 750 increased performance by approximately 30% in most situations. The design was so successful that it quickly beat the PowerPC 604e in integer performance and a planned successor to 604 was scrapped.

The PowerPC 740 is completely pin compatible with the older 603, allowing upgrades to the PowerBook 1400, 2400, and even a prototype PowerBook 500/G3.

The PowerPC 750 was used in many computers from Apple, including the original iMac.

RAD750

RAD750 is a radiation-hardened processor, based on the PowerPC 750. It is intended for use in high radiation environments such as experienced on board satellites and other spacecraft. The RAD750 was released for purchase in 2001. The Mars Reconnaissance Orbiter spacecraft has a RAD750 on board.

The processor has 10.4 million transistors, is manufactured by BAE Systems using 250 nm process and has a die area of 130 mm². It oprerates at 133 - 166 MHz. The CPU itself can withstand 200,000 Rads and temperature ranges between –55ºC and 125ºC. The RAD750 packaging and logic functions has a price tag in excess of US$200,000: the high price is mainly due to radiation hardening revisions to the PowerPC 750 architecture and manufacturing, stringent quality control requirements, and extended testing of each processor chip manufactured.

PowerPC 745/755

Motorola revised the 740/750 design in 1998 and shrunk die size to 51 mm² thanks to a newer aluminium based fabrication at .22 μm. The speeds increased to up to 600 MHz. The 755 were used in some iBook models. After this model, Motorola chose not to keep developing the 750 processors in favour of their PowerPC 7400 processor and other cores.

PowerPC 750CX

IBM continued developing the 750 line and introduced 750CX (codename Sidewinder) in 2000 with 256 KiB on-die L2 cache; this increased performance while reducing power consumption and complexity. At 400 MHz, it drew under 4 W. The 750CX had 20 million transistors including its L2 cache. It had a die size of 43 mm² through a 0.18 μm copper process. 750CX was only used in one iMac and iBook revision.

PowerPC 750CXe

750CXe (codename Anaconda), introduced in 2001, was a minor revision of 750CX which increased its frequency up to 700 and memory bus to 133 MHz, from 100 MHz. The 750CXe also featured improved floating-point performance over the 750CX. Several models of iBook and the last G3 based iMac used this processor.

A cost reduced version of 750CXe, called 750CXr, is available at lower frequencies.

Gekko

Gekko is the custom central processor for the Nintendo GameCube game console. It is based on a PowerPC 750CXe and adds about 50 new instructions as well as a modified FPU capable of some SIMD functionality. It has 256 KiB of on die L2 cache, operates at 485 MHz with a 162 MHz memory bus, is manufactured by IBM on a 180 nm fabrication processor. The die is 43 mm² large.

PowerPC 750FX

The 750FX (codenamed Sahara) came in 2002 and increased frequency up to 900 MHz, the bus speed to 166 MHz and the on-die L2 cache to 512 KiB. It also featured a number of improvements to the memory subsystem: an enhanced and faster (200 MHz) 60x bus controller, a wider L2 cache bus, the ability to lock parts of the L2 cache. It is manufactured using a 0.13 μm copper based fabrication with Low-K dielectric and Silicon on insulator technology. 750FX has 39 million transistors, a die size of 35 mm² and consumes less than 4 W at 800 MHz at typical loads. It was the last G3 type processor used by Apple.

A low powered version of 750FX is available called 750FL.

PowerPC 750GX

750GX (codenamed Gobi), revealed in 2004 is the latest and most powerful G3 processor from IBM. It has a on-die L2 cache of 1 MiB, top frequency of 1.1 GHz, support bus speeds up to 200 MHz among other enhancements compared to 750FX. It is manufactured using a 0.13 μm copper based fabrication with Low-K dielectric and Silicon on insulator technology. The 750GX has 44 million transistors, a die size of 52 mm² and consumes less than 9 W at 1 GHz at typical loads.

A low powered version of 750GX is available called 750GL.

PowerPC 750CL

750CL is an evolved 750CXe, with speeds ranging from 400 MHz to 1 GHz with a system bus up to 240 MHz, L2 cache prefetch features and graphics related instructions have been added to improve performance. As the added graphics-related functions match closely the ones found in the Gekko processor it is very likely that the 750CL is a shrink of the same processor for general purpose use. The 750CL is manufactured using a 90 nm copper based fabrication with Low-K dielectric and Silicon on insulator technology. It has 20 million transistors and the die is 16 mm² small. It draws up to 2.7 W at 600 MHz, 9.8 W at 1 GHz.

Broadway

It is believed but not confirmed that the processor in the Nintendo Wii game console is either a 750CL or a modified version of it. For instance, it runs at reported 729 MHz, a frequency not supported by stock 750CL. It measures only 4.2 x 4.5 mm (18.9 mm²). This is smaller than half the size of the "Gekko" microprocessor (43 mm²) incorporated in the GameCube at its first release. The chip may contain more instructions or higher SIMD support similar to the modifications made to the Gekko off the base 750CXe.

Future

IBM has ceased to publish a roadmap to the 750 family, in favor of marketing themselves as a custom processor vendor. Given IBM's resources, the 750 core will be produced with new features as long as there is a willing buyer. Available details on architectures such as Broadway and Gekko vary, however, and it is unclear how closely such designs are related to the "family."

In particular, IBM has no public plans to produce a 750-based microprocessor with better than 90 nm manufacturing technology, effectively phasing it out as a commodity chip competitive in such markets as networking equipment.

Freescale have all but abandoned all 750 designs in favour of e500 core based designs (PowerQUICC III).

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