Power Macintosh G4 is the name given to nine generations of high-end Macintosh computer hardware. These different hardware revisions were released between September 1999 and June 2003. The common thread joining the various models is the PowerPC G4 processor, aka the PowerPC 7400 and PowerPC 7450 processors from Motorola. The 7450 is sometimes termed the G4e to distinguish it from the earlier 7400, but Apple refers to both as the G4.
The G4 was a major step up from its predecessor, the PowerPC G3. The G3's floating-point unit, derived from the low-end second-generation PowerPC 603, was replaced with one derived from the higher-power PowerPC 604, leading to considerably higher floating-point performance. There were other improvements across the board, but the major architectural improvement between the G3 and G4 was the addition of a powerful SIMD vector unit that Motorola named AltiVec and Apple named the Velocity Engine. This vector extension was considerably more advanced than the contemporaneous vector extensions from Intel (SSE) and AMD (3DNow!). This extension was responsible for high performance on a number of benchmarks, most notably Photoshop.
AltiVec also helped on a number of synthetic benchmarks of floating-point performance; at the introduction of the G4 it was tested at as much as 3.2 gigaflops. At the time, the US government definition of a supercomputer was a computer running at more than 1 gigaflop, allowing the G4 to qualify. From this, Apple's marketing had a field day, trumpeting the Power Mac G4's status as a "desktop supercomputer" wherever it possibly could. (The flip side of this is that it also qualified for US export controls, which were quickly adjusted when the Playstation 2 also qualified.) The PowerPC G4 also had strong support for symmetric multiprocessing, something that would really help Apple through the lifetime of the G4.
A Convoluted Introduction
The product line that debuted in September 1999 actually contained two separate models. The "Yikes!" G4 was the the slower of the two models and had essentially identical internals to the preceding "Blue and White" G3, with minimal modifications to support a G4 CPU. The "Sawtooth" G4, on the other hand, had a fully redesigned motherboard, with added AGP graphics, support for booting from a USB drive, support for Apple's AirPort wireless networking card, and a standard DVD-ROM drive instead of CD-ROM. Both models shipped in the same style plastic case as the Blue and White G3, redone in sober graphite grey.
The original G4 lineup had a "Yikes!" machine at 400 MHz, and "Sawtooth" machines at 450 and 500 MHz. However, Motorola had production problems with the initial G4 CPUs, and Apple passed this on to their customers in October 1999, replacing all of these models with otherwise identical models 50 MHz slower. Annoyingly, the prices of these new models were the same as the faster machines they replaced. The lowest-end (350 MHz) model was quietly upgraded to a "Sawtooth" in December, and the line was returned to its original speed grades in February 2000.
Unfortunately, at this same time Intel and AMD were engaged in their mad dash to release a 1 GHz processor, which they both accomplished (with different degrees of availability) in March 2000. By mid-2000, 600 to 800 MHz Athlon and Pentium III machines were by no means uncommon, and the faster x86 processors overcame their architectural disadvantage to run rings around the G4. Apple thus resorted to one of the G4's other advantages; its multiprocessing facility.
In August 2000, Apple replaced the 450 and 500 MHz G4 machines with dual-processor G4s at the same price. These new machines also came standard with Gigabit Ethernet; an oddity in 2000. (They also launched the ill-fated G4 Cube at that time.) Unfortunately for Apple, their present operating system, Mac OS 9, had weak support for multiprocessor machines, and the advanced Mac OS X was still in beta. Thus, with a few notable exceptions, like the omnipresent Photoshop, the second processor remained mostly unused. The low-end 400 MHz version remained uniprocessor along with the Cube.
New speed grades finally appeared in January/February 2001; first 466 and 533 models in January, and then 667 and 733 MHz models in February. The latter two models used the newly-improved PPC 7450 or "G4e", finding themselves competitive with the early Pentium 4 systems pushed by Intel (which, frankly, were rather disappointing for 1.5 GHz machines). All of these 2001 models had small hardware redesigns and were ready for OS X, which finally arrived in March of that year. This revision of the G4 also introduced Apple's SuperDrive DVD burner, an expensive rarity in 2001. The SuperDrive would be a hallmark of the higher-end G4 models for the rest of the G4's lifetime. (Old-time Mac-heads will remember that "SuperDrive" originally referred to Apple's 1.44MB high-density floppy drive, circa 1990.)
A New Look
Throughout all of this internal modification, the G4 tower retained the same "graphite" appearance. This would change with the introduction of the "Quicksilver" G4 in July 2001, replacing stippled dark grey casing with shiny silver-grey surfaces. The initial models had single 733 and 867 MHz processors, and after a month of manufacturing delays they were joined with a dual 800 MHz machine. Despite the modest speed increases, the clock speeds of these processors were beginning to look rather pedestrian next to 2 GHz Pentium 4 and 1.5 GHz Athlon XP processors, and their performance was, as well. Apple's marketing department, which two short years previous had been crowing about "desktop supercomputers", was now beginning to panic.
A minor marketing coup was made with the January 2002 Quicksilver refresh; at this point the G4 line included 800, 933, and dual 1000 MHz models. At this point, they could claim to have a 2 GHz machine to compete with the speed demons from Intel and AMD, albeit with measures beyond those employed by Intel. (AMD was partway in between; their Athlon XP "2000+" runs at 1.67 GHz.) OS X was beginning to stabilize as well, allowing Mac users to take advantage of the second processor on the top-of-the-line behemoth.
DDR and Rumours of G5
CPU clock speed wasn't the only technological measure that the G4 was becoming deficient in by mid-2002. The x86 world switched to faster Double Data Rate (DDR) RAM through 2001, while the high-end G4 models plugged along with the older "SDR" technology. Also, the system bus speed in the x86 world was skyrocketing, with AMD doubling up on the clock rate and Intel quadrupling up to feed their fast processors with large quantities of data. Next to the effective 266 MHz Athlon bus and effective 533 MHz Pentium 4 bus, the 133 MHz G4 bus was starving the increasingly-faster processors for data. The Quicksilver models had additional "Level 3" processor cache to mitigate this problem, but such things can only go so far.
Apple worked towards fixing these problems in the August 2002 "Mirrored Drive Door" G4s. The name refers to minor cosmetic changes in the front bezel, but the more important changes were the switch to DDR RAM and a 167 MHz system bus. With Intel approaching 3 GHz with their Pentium 4, multiprocessor was again extended throughout the line; this series of G4 machines had dual 867 MHz, 1 GHz, or 1.25 GHz processors, standard.
As 2003 began, AMD was putting the finishing touches on their next-generation, 64-bit Opteron and Athlon 64 processors, and Intel had hit 3 GHz with their Pentium 4. The G4 was starting to look old; four years is a long time for a microprocessor design. IBM was rumoured to be working on a desktop variant of their POWER4 workstation/server processor, which would be a full 64-bit PowerPC and run at speeds up to 2 GHz. Everybody assumed that this chip would be used by Apple in a new generation of Power Mac, but they remained tight-lipped in January, again refreshing the familiar G4 with a stingy clock-speed increase to 1.0 GHz, dual 1.25 GHz, and dual 1.42 GHz. Unlike other G4 models, these G4s require OS X and will refuse to boot the classic Mac OS, and they sport zippy new FireWire 800 ports.
The End of the Line
The rumours of the new IBM processor turned out to all be true: the PowerPC 970 would be fully 64-bit, run at speeds up to 2 GHz, have a blazing 800 MHz-1 GHz system bus, and of course, appear in a new Power Mac, the Power Macintosh G5. Alongside the introduction of the imposing new aluminum G5 in June 2003, Apple released one last G4 revision: single- and dual-processor machines at 1.25 GHz. These machines were actually a small step backwards; their internals followed not the January 2003 models but the older August 2002 models, lacking FireWire 800 and retaining the ability to boot OS 9. This low-key revision was available for almost a full year and was discontinued on June 6, 2004, ending the desktop G4 series.
The Power Macintosh G4 series was Apple's flagship computer through a rather tough time for the computer manufacturer. Competition in the commodity x86 market drove performance to unheard-of levels while Apple's own processor supplier, Motorola, concentrated on the lucrative embedded systems market where performance is always secondary to other factors such as power consumption and price. Flagging computer revenues led Apple to search for other sources of income, which they eventually found in the iPod and iTunes Music Store. Ultimately, the G4 has been overshadowed by its nifty portable equivalent, the PowerBook G4 and by its behemoth successor the Power Macintosh G5, but for its time it remained a well-engineered, if sometimes underpowered, machine.
Sources: Low End Mac (http://lowendmac.com/ ) for Mac specifications, The Tech Report (http://techreport.com/ ) for x86 specifications, Wikipedia for G4 processor details, plus readings of various technology news sites throughout the G4's lifetime.
This writeup is copyright 2005 D.G. Roberge and is released under the Creative Commons Attribution-NoDerivs-NonCommercial licence. Details can be found at http://creativecommons.org/licenses/by-nd-nc/2.0/ .