The Power Mac G5 is Apple Inc.'s marketing name for models of the Power Macintosh that
contained the IBM PowerPC G5 CPU inside an anodized aluminium chassis. The professional-grade
computer was the most powerful in Apple's lineup when it was introduced, widely hailed
as the first 64-bit PC, and was touted by Apple as the fastest personal computer ever
built. It was officially launched as part of Steve Jobs' keynote presentation in June
2003 at the Worldwide Developers Conference, and saw three revisions to the line before
being retired in August 2006 to make way for its Intel replacement, the Mac Pro.
Introduction The Power Mac G5 was introduced with three
models, sharing the same physical case, but differing in features and performance. The
physical case of the Power Mac G5 was very different and unusual compared to any other
computer at that time. Many potential buyers were surprised to find that the attractive
case, while somewhat larger than the G4 tower it replaced, had room inside for only one
optical, and two hard drives. Steve Jobs stated during his keynote presentation
that the Power Mac G5 would reach 3 GHz "within 12 months." This would never come to pass;
after three years, the G5 only reached 2.7 GHz and was able to support 16 GB of RAM before
it was replaced by the Intel Xeon-based Mac Pro, which included processors with speeds
of up to 3 GHz. During the presentation, Apple also showed
Virginia Tech's Mac OS X computer cluster supercomputer known as System X, consisting
of 1100 Power Mac G5s operating as processing nodes. The supercomputer managed to become
one of the top 5 supercomputers that year. The computer was soon dismantled and replaced
with a new cluster made of an equal number of Xserve G5 rack-mounted servers, which also
use the G5 chip running at 2.3 GHz. PowerPC G5 and the IBM partnership
The PowerPC G5 is based upon IBM's dual-core POWER4 microprocessor. At the Power Mac G5's
introduction, Apple announced a partnership with IBM in which IBM would continue to produce
PowerPC variants of their POWER processors. According to IBM's Dr. John E. Kelly, "The
goal of this partnership is for Apple and IBM to come together so that Apple customers
get the best of both worlds, the tremendous creativity from Apple Computers and the tremendous
technology from the IBM corporation. IBM invested over $3 billion US dollars in a new lab to
produce these large, 300 mm wafers." This lab was a completely automated facility located
in East Fishkill, New York, and figured heavily in IBM's microelectronics strategy above and
beyond the partnership with Apple. The original PowerPC 970 had 50 million transistors
and was manufactured using IBM CMOS 9S at 130 nm fabrication process. CMOS 9S is the
combination of SOI, low-k dielectric insulation, and copper interconnect technology, which
were invented at IBM research in the mid-1990s. Subsequent revisions of the "G5" processor
have included IBM's PowerPC 970FX, and the PowerPC 970MP. Apple refers to the dual-core
PowerPC 970MP processors as either the "G5 Dual", or Power Mac G5 Quad.
Architecture
The Power Mac G5 line in 2006 consisted of three, dual-core PowerPC G5 configurations,
which can communicate through its FSB at half its internal clock speed. Each processor in
the Power Mac G5 has two unidirectional 32-bit pathways: one leading to the processor and
the other from the processor. These result in a total bandwidth of up to 20 GB/s. The
processor at the heart of the Power Mac G5 has a "superscalar, superpipelined" execution
core that can handle up to 216 in-flight instructions, and uses a 128-bit, 162-instruction SIMD unit.
All modern 32-bit x86 processors since the Pentium Pro have the Physical Address Extension
feature, which permits them to use a 36-bit physical memory address to address a maximum
of 236 bytes of physical memory, while the PowerPC 970 processor is capable of addressing
242 bytes of physical memory and 264 bytes of virtual memory. Due to its 64-bit processor
the Power Mac G5 has a RAM capacity greater than the 4 GB addressable memory limit of
traditional 32-bit processors. The final revision of the Power Mac G5 can hold 16 GB of Dual-Channel
DDR2 PC4200 RAM using eight memory slots, with support for ECC memory.
Product revision history DP designates a dual-processor machine, SP
designates a single-processor machine, and DC designates a dual-core-processor machine.
2003 June: Initial release at speeds of SP 1.6, SP 1.8, DP 2.0 GHz.
2003 November: DP 1.8 replaces SP 1.8 GHz; price reduction on SP 1.6 GHz.
2004 June: 90 nm DP 1.8, DP 2.0 and DP 2.5 GHz replace all previous models. The 2.5 GHz
model is notable as the first major PC with liquid cooling included as stock.
2004 October: A new SP 1.8 reintroduced, with a slower, 600 MHz FSB, PCI bus, based upon
the iMac G5's architecture. Apple's official name for this machine is "Power Mac G5".
2005 April: CPU speed increased: DP 2.5 GHz → DP 2.7 GHz, DP 2.0 GHz → DP 2.3 GHz,
DP 1.8 GHz → DP 2 GHz. Newly introduced features were the 16x dual-layer SuperDrives
across the line and increased storage, up to 800 GB for the higher-end models. The 1.8 GHz
SP was not modified. 2005 June–July: The SP 1.8 model was discontinued
in the United States and Europe. 2005 October: Shift to dual-core processors:
DP 2.0 GHz → DC 2.0 GHz, DP 2.3 GHz → DC 2.3 GHz, DP 2.7 GHz → DP DC 2.5 GHz,
all with DDR2 memory, and PCI Express expansion in place of PCI-X. The older PCI-X, DP 2.7 GHz
model remained available for a while, but the slower speed single-core models were discontinued
immediately. 2006 August: The Power Mac is replaced by
its Intel successor, the Mac Pro. Defects
Early versions of dual processor G5 computers have noise problems. The first one is ground
loop-based interference, which sometimes causes noise leaks into the analog audio outputs.
This bug was fixed in Rev. B G5. The second noise problem came from the 'chirping'
sound, which can be triggered by fluctuations in power draw. For example, showing and hiding
the Dock makes a brief chirp. Many had blamed the power supply used in the G5 as the cause,
but this theory has never been confirmed. A very effective work-around is to disable
the CPUs' "nap" feature using Apple's CHUD Tools, but this was not recommended by Apple.
This noise problem was not fixed until the dual core generation of G5s was produced,
however it did not affect the "Late 2004" model. The power draw fluctuation was later
attributed to the lack of power management features in the single-core processors. Apple
eventually posted the chirping bug information on its support site.
Although the noise problems did not prevent the affected computers from working, they
were problematic for audio professional and enthusiasts alike, especially for the liquid-cooled
models, which had been expressly designed as mechanically quiet for discerning listeners.
Some 2.5 GHz dual processor and all 2.7 GHz dual-processor and the 2.5 GHz quad-processor
variant were cooled by a liquid cooling system that consisted of a radiator, coolant pump,
and heat exchangers that were bolted to the processors. The cooling system was made by
Delphi, a former Harrison Radiator Division of General Motors. This was a bold step for
Apple, and should have allowed the use of very fast processors, giving Apple an advantage
in both the performance and reliability race, but the LCS turned out to be subject to coolant
leakage. If not caught in time, the leakage can destroy the processors, logic board, and
even corrode the aluminium casing itself. While leakage was sometimes detectable by
drops of green coolant in or beneath the machine, in many machines the seepage is so slight
that it was almost impossible to detect without dismantling the entire computer. Later models
were equipped with a Panasonic LCS which was much more reliable.
The LCS system fits into the case where the heat sinks would normally go, so there is
no easy way to distinguish the liquid-cooled versions from the air-cooled, although most,
but not all, of the LCS versions have a sticker inside warning about the possibility of leakage.
P.A. Semi's G5 derivative When P.A. Semi announced the preliminary pre-production
plan of PWRficient processor, there had been persistent rumors that Apple would prepare
for its use in its professional line of personal computers.
In 2006, The Register reported that P.A. Semi had formed a tight relationship with Apple,
which would result in P.A. Semi promptly delivering processor chips for Apple's personal computer
notebook line and possibly desktops. Even in 2006, Apple did not have a laptop version
of G5 processor. The processor that would run the personal computers was P.A. Semi's
preliminarily proposed processor, PWRficient 1682M. The version that would be sampled for
pre-production at third quarter of 2006 was a 2 GHz, dual-core CPU with two DDR2 memory
controllers, 2 MB of L2 cache, and support for 8 PCI Express lanes. The sampled chip
also has lower heat intensity than Intel's Core Duo, which gives off 9–31 W under normal
load. According to The Register article, P.A. Semi
executives believed they were all but assured winning Apple's contract, and CEO Dan Dobberpuhl
thought Apple's hints of moving to Intel were just a persuading tactic. At the time, the
companies were working for PWRficient software. Despite the advantages of more compatible
architecture, Apple moved to the Intel architecture officially for 'performance-per-watt' reasons.
However, P.A. Semi would not be able to ship its low-power multicore product in volume
until 2007, which, combined with P.A. Semi's status as a start-up company, seems to have
been the final blow to the development of Power Mac computers. However, it was also
speculated that Apple switched to Intel processor because Apple could no longer abide the constant
delays in performance ramp up, desired native Windows compatibility, or it was Apple's strategy
to shift its business focus away from desktop computing to iPod) development.
Notes
External links Ars Technica: Inside the PowerPC 970
Ars Technica: A Brief Look at the PowerPC 970
Ars Technica Review: Power Mac G5 Dual 2.5 GHz
Forevermac.com: The Power Mac G5 Quad Core 2.5 GHz