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 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has been replaced by the Intel-based MacBook Pro.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 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. 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 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 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
thanks to an improved cache coherency protocol and a 64-bit floating point
unit, 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.
PowerPC 7410 The PowerPC 7410 "Nitro" is a low-power
version of the 7400 but it was manufactured at 180 nm instead of 200
nm. Like the 7400 it has 10.5 million transistors. It debuted in the PowerBook
G4 on 9 January 2001. The chip added the ability to use all or
half of its cache as high-speed, non-cached memory mapped to the
processor's physical address space as desired. This feature was used by
embedded systems vendors such as Mercury Computer Systems.
PowerPC 7450 The PowerPC 7450 "Voyager"/"V'ger" was
the only major redesign of the G4 processor. The 33-million transistor
chip extended significantly the execution pipeline of 7400 to reach
higher clock speeds, improved instruction throughput to compensate for
higher instruction latency, replaced an external L2 cache with an integrated
one, supported an external L3 cache, and featured many other architectural
advancements. The AltiVec unit was improved with the 7450; instead of
executing one vector permute instruction and one vector ALU instruction per cycle
like 7400/7410, the 7450 and its Motorola/Freescale-followers can execute
two arbitrary vector instructions simultaneously. It was introduced with
the 733 MHz Power Mac G4 on 9 January 2001. Motorola followed with an interim
release, the 7451, codenamed "Apollo 6", just like the 7455.
The enhancements to the 745x design gave it the nicknames G4e or G4+ but these
were never official designations. PowerPC 7445 and 7455
The PowerPC 7455 “Apollo 6” was introduced in January 2002. It came with
a wider, 256-bit on-chip cache path, and was fabricated in Motorola's 0.18 µm
HiPerMOS process with copper interconnects and SOI. It was the first
processor in an Apple computer to pass the 1 GHz mark. The 7445 is the same
chip without the L3 cache interface. The 7455 is used in the AmigaOne XE G4, and
the dual 1 GHz Power Mac G4 PowerPC 7447 and 7457
The PowerPC 7447 "Apollo 7" is slightly improved from the 7450/55, it has a 512
KB on-chip L2 cache and was manufactured in a 130 nm process with SOI, hence
drawing less power. It has 58 million transistors. With the 7447A, which
introduced an integrated thermal diode as well as DFS Freescale was able to
reach a slightly higher clock. The 7457 has an additional L3 cache interface,
supporting up to 4 MB of L3 cache, up from 2 MB supported by the 7455 and
7450. However, its frequency scaling stagnated when Apple chose to use the
7447 instead of the 7457, despite that the 7457 was the L3 cache-enabled
successor to the L3 cache-enabled 7455 that Apple used before.
The only companies that offer the 7457 in the form of upgrades for the Power
Mac G4, iMac G4, and Power Mac G4 Cube are Giga Designs, Sonnet Technology,
Daystar Technology and PowerLogix. The Pegasos computer platform from Genesi
also uses 7447 in its Pegasos-II/G4. PowerPC 7448
The PowerPC 7448 "Apollo 8" is an evolution of the PowerPC 7447A announced
at the first Freescale Technology Forum in June 2005. Improvements were higher
clock rates officially and easily up to 2.4 GHz through overclocking, a larger 1
MB L2 cache, a faster 200 MHz front side bus, and lower power consumption. It was
fabricated in a 90 nm process with copper interconnects and SOI.
PowerPC 7448 users were: Daystar for their High-Res Aluminum
PowerBook G4 upgrades NewerTech for their Power Mac G4
upgrades PowerLogix for their Power Mac G4 Cube
upgrade Cisco in NPE-G2 network processor module
for their 7200VXR routers e600
In 2004, Freescale renamed the G4 core to e600 and changed its focus from
general CPUs to high-end embedded SoC devices, and introduced a new naming
scheme, MPC86xx. The 7448 was to be the last pure G4 and it formed the base of
the new e600 core with a seven-stage, three-issue pipeline, and a powerful
branch prediction unit which handles up to sixteen instructions out-of-order. It
has an enhanced AltiVec unit capable of limited out-of-order execution and a 1
MB L2 cache. Device list
This list is a complete list of known G4 based designs. The pictures are
illustrations and not to scale. References
Diefendorff, Keith. "PowerPC G4 Gains Velocity". Microprocessor Report. pp.
10–15. Gwennap, Linley. "G4 Is First PowerPC
With AltiVec". Microprocessor Report. Halfhill, Tom R.. "PowerPC Ain't Dead
Yet". Microprocessor Report. pp. 13–15.