Does MHz Matter?

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Speed. Whether you need a new Mac that'll give you more of it or you want to wring as much as possible from the machine you've got, speed is what it's all about. If you've ever waited and waited for a Microsoft Excel calculation to finish or for an Adobe Photoshop filter to appear, pixel . . . by . . . pixel, you know what we're talking about.

It's easy to look at the clock speed of a Mac's processor--measured in megahertz--as the prime indicator of the computer's speed. But your hard drive, your RAM, your video card, and many other parts of your Mac also affect its speed.

That MHz number in your Mac's name does matter--but it's far from the only factor. To gauge how different components can optimize a system's performance, we enlisted the expertise of Macworld Lab. When you see what we found, you'll never look at MHz the same way again.

Quest for Speed

Your processor can be thought of as your Mac's brain, but a lot of other hardware inside your computer helps to process and transfer information. Each piece can significantly affect your system's overall speed. (See "Your Mac's Inner Life" for how everything works together.)

Your Mac can read and write data much faster to RAM than to your hard drive, so the more RAM you have, the more data your Mac can keep at the ready. Photoshop, for example, places into RAM as much information as possible about the images it's editing. When there's no more real memory available, the rest of the data is stored on the hard drive. If you've ever edited a large image in Photoshop on a system with very little RAM, you know that when the hard drive comes into play, you must sit and wait.

Though the hard drive can't move data as quickly as RAM, it still has the ability to affect performance in a major way. Regardless of its size, a faster hard drive will certainly speed up your work when memory-intensive applications such as Photoshop run out of RAM and begin storing data on the disk. And many applications--FileMaker is one example--spend most of their time reading and writing data on the hard drive.

Then there's the video card, which dramatically affects image-intensive features such as scrolling speeds, screen redraws, and the frame rates of 3-D action games.

Which of these subsystems are most vital for you to consider when you're shopping for a new system or upgrading your current one? The answer depends on how you use your Mac.

The Processor

The Mac Classic II that Apple sold ten years ago had a 16MHz processor. Today's fastest Power Mac G4s run at 733MHz. But does multiplying megahertz by 45 really mean 45 times the speed? When is an incremental boost in processor speed worth its price? When is a dual-processor system a prudent choice?

To analyze the power of the processor, Macworld Lab tested several models: singleand dual-processor 533MHz Power Mac G4s; a single-processor 733MHz Power Mac G4; and a 450MHz blue-and-white Power Mac G3, with and without a PowerLogix G4 upgrade card.

Basic Tasks For most basic tasks, such as starting up your Mac and using the Finder, a faster processor won't gain you anything. However, for a few basic, processor-intensive tasks, you do benefit: unstuffing a file in our trials went 7 percent faster on the 733MHz G4 than on the 533MHz G4, and encrypting a file using Apple's Encrypt command was about 12 percent faster. (See our test results in "Variations on a Mac.")

In Microsoft Office tests, the power of a faster processor was evident--the 733MHz G4 beat the 533MHz model in all five of those tests. Most impressive: the faster processor was worth a 21 percent edge in scrolling through an Excel document.

Graphics and Media When it came to Photoshop, the 733MHz Power Mac was only negligibly faster at most of the tasks than the 533MHz system (see " Putting Photoshop to the Test "). Where the processor speed really seemed to make a difference, however, was when we converted an RGB image to the CMYK color space. The 733MHz Mac did the task 30 percent faster.

Audio and video applications also demand processor power--as our MP3 and video-export tests demonstrated.

Games can also be very processor-intensive. In our Quake III tests, the 733MHz system displayed 14 percent more frames per second than the 533MHz machine. The result was more-fluid game animations and a far more enjoyable gaming experience.

The Dual-Processor Difference Mac users can once again choose a computer with two processors. In Mac OS 9, an application that is written to take advantage of both processors (such as Photoshop) can spin off tasks to the second proces-sor. In Mac OS X, applications native to OS X can run on either processor, and tasks use the processors more equally (see " Double Vision," November 2000).

In our tests, the dual-processor 533MHz model showed its best results, predictably, in Photoshop. In four of six tests, the dual-processor system beat its single-processor cousin, shaving more than 20 percent off the time needed to complete a Gaussian blur, for example.

The 3-D application Cinema 4D XL, from Maxon, also takes advantage of multiple processors. When rendering a model--a very processor-intensive task--the dual-processor Mac cut nearly half off the time of the single-processor 533MHz machine, and it cut more than a third off the 733MHz Mac's time. In tests of software not optimized for multiple processors, however, the dual-processor Mac offered little or no advantage.

G3 versus G4 Another choice you have as a Mac user is between the G3 processor used in Apple's consumer systems (the iMac and iBook) and the G4 processor used everywhere else. The two are very similar, except for AltiVec--Apple calls it Velocity Engine--on the G4. It gives G4-savvy applications (Photoshop is one) an extra boost in speed.

We explored the differences between the G3 and G4 by pitting a 450MHz blue-and-white Power Mac G3 system against itself--with a 450MHz G4 upgrade card inside.

The two configurations were neck-and-neck in most Finder and Office tests; however, the G4 chip came through on features designed to take advantage of AltiVec. Our upgraded G4 system performed a Gaussian blur in Photoshop in half the time it took the original system, and it also rendered lighting effects faster. In MP3 encoding, the upgraded system shaved 36 percent off the G3's time.

The Bottom Line Just look at the difference between similarly configured Power Mac G4s, one running at 533MHz, the other at 733MHz: the latter model has a clock speed nearly 40 percent faster (and at press time, it cost roughly $500 more). Yet in most of our tests, it provided a less-than 10-percent improvement, and in only a handful did it make a difference of 20 percent or more.

Faster or multiple processors generally mean faster computers, but the difference won't matter much unless you spend most of your time in a 3-D, graphics, or video-editing application. Even then, RAM might give you more bang for your buck. If you do a lot of work with graphics, the horsepower of a faster processor will help, but an extra processor will help even more--if the applications you use are multiprocessor-aware, and especially if you're using Mac OS X.


The more RAM you have, the more information you can store there. That means fewer trips to your relatively slow hard drive. And although RAM prices fluctuate, lately they've been as low as prices on the stock market. So when does adding RAM make sense? To find out, we retested our 533MHz G4 after increasing its puny 128MB of RAM to a total of 768MB.

Basic Tasks In most general-use areas, adding RAM to our test systems made little difference. However, it's important to note that the more RAM you have, the more applications you can run simultaneously. That's not technically a speed gain, but being able to switch between open applications instead of having to quit some before launching others certainly helps productivity.

Mac OS also offers built-in virtual memory; turning it on sets aside part of your hard drive to be used as memory when your RAM fills up. But hard drives are slower than RAM. If you rely on virtual memory to keep all your favorite applications open, adding RAM instead will dramatically improve your system's responsiveness.

Graphics and Media In Photoshop work, you manipulate a lot of information. Every time you run a filter, that filter must analyze and modify every last pixel of your image. The more image information you can keep in RAM, the faster Photoshop runs.

So when we added 640MB of RAM to our test system, Photoshop began to fly. Rotating and applying lighting effects to an image went twice as fast as they did on the original 128MB system. The extra RAM tripled the system's scores in the Gaussian Blur and Unsharp Mask tests. And resizing an image was four times as fast with the added RAM.

Outside of Photoshop, additional RAM didn't make much difference in test results. The system's performance in our iMovie test was slightly better with the additional memory, but scores in our Cinema 4D XL, SoundJam, and Quake tests were essentially unchanged.

Dual Processors We also added RAM to our dual-processor 533MHz and single-processor 733MHz Power Mac G4s, and we tested them with Photoshop. The result was an impressive display of Apple's dual-processor technology: the dual-processor system was clearly faster than the 733MHz system in four of our six tests.

Massive amounts of RAM and two G4 processors are the most potent combination any Photoshop professional could want.

The Bottom Line If you're a Photoshop pro, RAM is where it's at. We saw tremendous gains when we added memory, especially on the dual-processor G4. If Photoshop is not your main application, more RAM won't bring huge speed gains, but it can help if you run many applications simultaneously or rely on virtual memory.

The Hard Drive

Writing to or from a hard drive has traditionally been a performance bottleneck for Macs. Processors had to wait around for slow hard drives to provide them with data. The sure-fire way to speed up a Mac II was to buy a speedy new hard drive.

We tested three hard drive configurations in our 533MHz G4: its built-in 7,200-rpm Maxtor ATA-100 drive; a slower 5,400-rpm Western Digital ATA-66 drive; and a RAID array with two 36GB Seagate 10,000-rpm drives connected via Adaptec's 39160 Ultra 160 SCSI card.

Putting Photoshop to the Test

Few applications expose a Mac's deficiencies better than Adobe Photoshop. We ran a series of Photoshop tests on each of our various Mac configurations. Since RAM is a major factor in Photoshop performance, we tested each system twice--once with 128MB of RAM and a second time with 768MB.
Best results in bold. RAM Gaussian Blur Unsharp Mask Resize RGB to CMYK Rotate Canvas Render Lighting effects
Apple Power Mac G4/533 128MB :16 :15 :08 :23 :18 :13
768MB :05 :05 :02 :20 :09 :06
  with 5,400-rpm IDE drive 128MB :27 :23 :18 :24 :28 :15
768MB :05 :05 :02 :20 :09 :06
  with two 10,000-rpm Ultra 160 SCSI drives in striped RAID array 128MB :13 :12 :05 :23 :15 :11
768MB :05 :05 :02 :20 :08 :06
  with ATI Radeon PCI graphics card 128MB :15 :15 :08 :23 :19 :15
768MB :05 :05 :02 :20 :08 :06
  with ATI Rage 128 Pro AGP graphics card 128MB :14 :13 :08 :23 :13 :15
768MB :05 :05 :02 :21 :08 :06
Apple Power Mac G4/533 DP 128MB :12 :12 :08 :23 :16 :12
768MB :03 :03 :01 :20 :05 :04
Apple Power Mac G4/733 128MB :15 :14 :08 :16 :17 1:03
768MB :05 :05 :01 :12 :07 :06
Apple Power Mac G3/450 with 128 RAM 1:02 :32 :18 :36 :36 :38
  with 450MHz G4 upgrade card :31 :31 :17 :37 :36 :29
smaller is better smaller is better smaller is better smaller is better smaller is better smaller is better
All scores are in minutes:seconds. We used a 50MB file and tested each system with a default system disk cache, virtual memory disabled, and displays set to 24-bit color and 1,024-by-768-pixel resolution. We set Photoshop History to Minimum. In tests with 768MB RAM, we set Photoshop's memory partition to 250MB; with 128MB of RAM, we set it to 75MB. --Macworld Lab testing by Jason Cox and James Galbraith

Basic Tasks The 5,400-rpm drive and 7,200-rpm drive were evenly matched in most of our Finder tests, but the RAID array was clearly faster than either. With this configuration, our system duplicated a 100MB test file in just over half the time it took the other drives.

Graphics and Media Photoshop likes lots of RAM, but once it runs out, it has to write data to the disk--and the faster the hard drive, the better. The RAID array had the fastest times, beating our 7,200-rpm drive on nearly every front. Resizing an image went nearly 40 percent faster on the RAID system. The 5,400-rpm drive was dead last in all our tests.

The Bottom Line For most common tasks, the speed of your hard drive won't make much difference. As our testing showed, a hard drive's effect is most apparent in disk-intensive programs such as Photoshop.

The advantage of a faster drive applies most to capturing and editing digital video and audio--tasks that involve gigantic amounts of data. For example, if you're a musician, you'll want a speedy drive so you can simultaneously play back multiple audio tracks.

But the cost of our high-end RAID system ($480 for a SCSI card plus $1,100 for two 10,000-rpm drives) makes it a serious investment for a graphics professional. Before you buy such a drive, consider adding a lot of RAM and a faster processor instead.

The Video Card

A Mac's video card draws everything you see on its monitor. Today's video cards are blazing fast, and most are designed to draw complicated graphics, such as the 3-D graphics in cutting-edge games, as fast as possible. To see how different video cards affected performance, we tested the G4/533 with its installed ATI Radeon AGP card and with an ATI Rage 128 Pro AGP. (We also tried it with a Radeon PCI card.)

Basic Tasks Most of these results weren't affected by the change in video cards. But for scrolling--which relies heavily on the power of your video card--the faster Radeon card clearly outperformed the Rage 128 Pro. The Radeon was 10 percent faster at scrolling a PDF file and 12 percent faster at scrolling in Excel.

Graphics and Media The Radeon has more RAM and is newer than the Rage 128 Pro, and that hit home in our gaming tests. In our Quake test, the Rage 128 Pro drew about 40 frames per second, compared with Radeon's 59 frames, which made for noticeably smoother game play.

The Bottom Line A better graphics card will speed up scrolling and support monitors with higher resolutions. If you are a graphics professional, improved scrolling speeds will save you some time. But the best reason to upgrade your video card is to play games on your Mac.

Other Factors

Several other things also affect performance. You can't upgrade your system bus, and most people won't upgrade their DVDor CD-ROM drives, but each of these has bearing on a Mac's speed.

System Bus A bus is a line of communication between your Mac's components. The system bus connects the processor to the RAM. Essentially, the faster your Mac's system bus, the faster your Mac's processor can work.

The latest Power Mac G4s feature a system bus that runs at 133MHz. The system bus on the PowerBook G4, G4 Cube, and iMac runs at 100MHz. iBooks have a slower 66MHz system bus.

Optical Drives A major quirk our tests revealed was that the 733MHz G4 took twice as long as our 533MHz G4 to install Quake from a CD. That's because the 733MHz model we tested uses Apple's new DVD-writing SuperDrive, which reads CD-ROMs much more slowly than the CD-R drive in the 533MHz G4.

The Last Word

Processor speeds measured in hundreds of megahertz are flashy, easy-to-compare numbers, but they don't tell the whole story. Your Mac's other components also have a lot to do with how fast it runs.

How you use your Mac on an everyday basis will determine which components mean the most to you (see "What Matters When?"). If you need to move large chunks of data--Photoshop pros, take note--loading up on RAM will generally do you more good than superfast hard drives and hyperclocked processors. Faster processors generally make for faster Macs, but they aren't good investments unless you spend a lot of time with processor-intensive 2-D, 3-D, or video applications. And if you're a gamer, spend some cash on a better video card and watch frame rates skyrocket along with your scores.

Whether you're shopping for a new Mac or just trying to squeeze more life out of your current system, look beyond megahertz: it will help you make a much wiser hardware investment.

Associate Editor JONATHAN SEFF specializes in Mac systems and multimedia.

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