Power Mac G5

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.^[1] The professional-grade computer was the most powerful in Apple's lineup when it was introduced, widely hailed as the first 64-bit personal computer, 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. Although somewhat larger than the G4 tower it replaced, the G5 tower 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 debuted with processors running at speeds of up to 3 GHz.

During the presentation, Apple also showed Virginia Tech's Mac OS X computer cluster supercomputer (a.k.a. supercluster) 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 inside of a Power Mac G5, late 2005 model

The PowerPC G5 (called the PowerPC 970 by its manufacturer, IBM) 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 larger microelectronics strategy.

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 (same basic design on a 90 nm process), and the PowerPC 970MP (essentially two 970FX cores on one die). Apple refers to the dual-core PowerPC 970MP processors as either the "G5 Dual" (for single-socket, dual-core configurations), or Power Mac G5 Quad (for dual-socket, four-core configurations).

Architecture

The PowerPC 970FX inside a PowerMac G5.

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 (AltiVec).

All modern 32-bit x86 processors since the Pentium Pro have the Physical Address Extension (PAE) feature, which permits them to use a 36-bit physical memory address to address a maximum of 2³⁶ bytes (64 gigabytes) of physical memory, while the PowerPC 970 processor is capable of addressing 2⁴² bytes (4 terabytes) of physical memory and 2⁶⁴ bytes (16 exabytes) of virtual memory. Due to its 64-bit processor (and 42-bit MMU), 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 (front-side bus), PCI bus, based upon the iMac G5's architecture (U3lite and Shasta chips). Apple's official name for this machine is "Power Mac G5 (Late 2004)".
• 2005 April: CPU speed increased: DP 2.5 GHz → DP 2.7 GHz (PCI-X, LC), DP 2.0 GHz → DP 2.3 GHz (PCI-X), DP 1.8 GHz → DP 2 GHz (PCI). 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 (termed a Quad Power Mac G5, with four CPU execution cores and more reliable liquid cooling), all with DDR2 memory, and PCI Express expansion in place of PCI-X.^[2][3][4] 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

The back of a late 2005 model.

Early versions of dual processor G5 computers have noise problems. The first one is ground loop-based interference,^[5] 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 (at least there have never been any reports). The power draw fluctuation was later attributed to the lack of power management features in the single-core processors.^[6] Apple eventually posted the chirping bug information on its support site.^[7]

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 (LCS) 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.^[8] 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 (only the 2.7GHz) were equipped with a Panasonic LCS which was much more reliable.^[9]

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,^[10] there had been persistent rumors that Apple would prepare for its use in its professional line of personal computers.^[11]

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.^[12] 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 (PA6T-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,^[13] desired native Windows compatibility, or it was Apple's strategy to shift its business focus away from desktop computing to iPod (and subsequently iOS (Apple)) development.

Apple acquired P.A. Semi in 2008,^[14] using P.A. Semi's engineering resources to develop ARM CPUs for their iPhone, iPod touch, iPad, and AppleTV product lines.^[15]

Notes

External links

Wikimedia Commons has media related to Power Mac G5.

• 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