Silencing the 'megahertz myth'


IBM Corp.

said this week that it will have a new 64-bit version of the PowerPC processor in production later next year, Macintosh users felt a rush of excitement: Could this be the magic bullet that reverses the Mac’s reputation as the speed laggard of the computing world?

Of course,

Apple Computer Inc.

hasn’t said a word about the new IBM chip -- the company never comments on such matters -- but several news organizations have reported that "sources close to the company" say Apple, based in Cupertino, Calif., plans to use it.

The news had several Mac Web forums buzzing.

"This chip can’t come fast enough," wrote someone on’s general discussion forum. "OS X will finally fly!"


"Needless to say," another wrote, "this is good news for Apple -- and the chip does not run software developed for



But past disappointments have left others skeptical.


"If this thing is going to be 1.8 gigahertz in late 2003, then this is of no help to Apple in combating the ‘megahertz myth,’" one person wrote.

"Unlike going to 32-bit, there are very few applications that will benefit from 64-bit," yet another MacCentral visitor wrote, cating doubt on the value of one of the IBM chip’s main features.

IBM, based in Armonk, N.Y., says its new processor -- called the PowerPC 970 -- will start at 1.8 gigahertz. That is significantly faster than the 1.25 gigahertz speed of the fastest G4 in current tower desktop Macs.

Speculation that the new processor would be a good fit for Macs arises from its compatibility with older versions of the PowerPC.

The chip also apparently includes the

Motorola Inc.

-invented "AltiVec" set of extra instructions -- Apple calls it the "Velocity Engine" -- that make the G4 chip in current Macs very good at processing such digital media files as photos and movies.

The appearance of an IBM chip in a Mac should be no surprise. The PowerPC line of processors resulted from a 1991 alliance between Apple, IBM and Motorola.

Although Motorola historically has supplied most of the PowerPCs found in Macs, IBM also has sold processors to Apple and currently supplies the G3 chips used in the iBook.

In recent years, Mac users have grumbled as Motorola, based in Schaumburg, Ill., has been unable to keep up with Intel Corp. in terms of processor clock speed, the "megahertz" (now "gigahertz") number featured so prominently in computer ads.

Intel’s fastest Pentium 4 runs at 2.8 gigahertz, more than twice as fast as the 1.25 gigahertz G4 PowerPC in Apple’s top-of-the-line Quicksilver tower.

Meanwhile, Apple has responded to this performance gap by calling it the "megahertz myth," and telling its customers that the PowerPC’s more efficient design means it can do more despite its slower speed.

Real-world tests have shown that, in general, a PowerPC G4 does outperform a Pentium 4 at the same clock speed. But in the real world, you can buy a mid-range Windows PC with an Intel processor running at more than twice the speed of an iMac -- and for less money.

IBM’s new PowerPC 970 would help address this nagging issue in two ways: First, the chip will be introduced at 1.8 gigahertz, so speeds exceeding 2 gigahertz should soon follow.

While Intel no doubt will have the Pentium well over 3 gigahertz by the time we see the 970, at least the gap will be smaller.

The second and more critical way the 970 helps is its 64-bit architecture. Although we’re deep in geek territory here, this aspect is critical to the IBM processor’s significance.

Put simply, the term "64-bit" describes the size of the chunks of data the chip can handle during a processing cycle. To get an idea of what a "bit" means, consider that a single typed character consists of eight bits.

The ability to digest bigger chunks of data means the chip can get more work done in each cycle. To the user, this means less time spent on such heavy-duty tasks as processing digital media.

The G3 and G4 chips in current Macs are 32-bit chips, as are Intel’s Pentium 4 and

Advanced Micro Devices Inc.

’s Athlon, both of which are used in Windows PCs.

Throughout the history of computing, processors have moved from 4 bits to 8 to 16 to 32 -- and, now, to 64 bits. Each increase has resulted in performance gains that have allowed computers to run more complex software. That’s how we’ve gotten from word-processing to editing digital video.

The other advantage a 64-bit processor has is the ability to address more memory. Today’s 32-bit Pentium and G4 chips have a limit of 4 gigabytes of memory.

While far more than the 256 megabytes to 512 megabytes most computer users now have in their machines, in five or six years, it probably won’t be enough.

That may seem improbable, but as computers have grown capable of increasingly complex tasks, their appetite for memory has grown accordingly.

Even a lowly 128 megabytes of random access memory (RAM) is 1,000 times more memory than the 128 kilobytes common in computers of the mid-1980s. The new IBM chip can address 4 terabytes of memory -- 1,000 times more than 4 gigabytes.

So, theoretically, a Mac armed with the new IBM chip -- with its fancy, 64-bit design and ability to address huge volumes of memory -- should be ideally suited to such demanding digital media challenges as editing movies, rendering 3D graphics and burning DVDs.

"This chip represents a substantial leap forward over the capabilities of the current G4 line," said Jon Stokes, who covers computer-processor issues for the Web site Ars

Stokes said IBM’s inclusion of the AltiVec code, for which much Mac software has been optimized, along with many other technical improvements "will make it a solid core around which Apple can build and extend its digital hub strategy."

Sounds terrific, but Apple still has some work to do.

In order to take full advantage of the PowerPC 970, Apple will need to rewrite parts of the Mac OS X operating system, now designed only for 32-bit PowerPCs.

And, then, all the software -- from Apple’s own built-in applications to Adobe Photoshop and


Office -- will have to be optimized for 64-bit processing.

IBM has said the new chip has a 32-bit mode, so older software will still run, but without the advantages of the 64-bit design.

What we’re really looking at here is a gradual transition from 32-bit to 64-bit computing, just as Apple moved from the old Motorola 68000 series of chips to the first PowerPCs in the mid-1990s.

The same transition will happen in the Windows world.

Both Intel and Advanced Micro have 64-bit chips; Microsoft has a 64-bit version of Windows, but for now it’s only for workstations that use the Intel chip.

One would expect that Apple already is working on a 64-bit version of Mac OS X to run on the PowerPC 970, samples of which IBM no doubt has supplied to Cupertino.

Mac users wondering when they will be able to get their hands on a 64-bit Mac will have to wonder for a while, since Apple never tips its hand.


Common sense, however, dictates that Apple most likely will introduce the chip in its business-oriented rack-mounted server, Xserve, perhaps in late 2003. The 970 would appear in Apple’s pro desktop models some months later. I wouldn’t expect to see an iMac with the chip until the middle of 2004 at the earliest.


But it’s something to dream about, isn’t it?