With a new aluminum - and - ice enclosure , the iMacs unveiled by Apple earlier this week look markedly different from their immediate predecessors . But the more modest change inside — a speed bump to the Intel Core 2 twosome scrap that powers the car — translate to only a slight rise in execution from one version of Intel - based iMacs to the next .

However , if you ’ve been dull to hop aboard Apple ’s transition to Intel processors , this latest iMac redevelopment may finally push you toward an upgrade . The top - of - the - line iMac outstrip the fastest PowerPC G5 - based iMac by 43 percent in our Speedmark 4.5 tests .

It ’s easy to nibble theseiMacsout from their white , plastic predecessors , thanks to an aluminum typeface with a black - framed , glistening LCD monitor . The 17 - inch model has been dropped from Apple ’s offer — instead Apple sport 20- and 24 - column inch iMacs , available in three configuration . The unexampled introduction - level $ 1,199 iMac features a 20 - in display , a 2GHz Core 2 Duo processor , an ATI Radeon HD 2400 XT graphics card with 128 MB GDDR3 computer storage , and a 250 GB hard drive . The mid - story $ 1,499 iMac sport the same 20 - inch CRT screen , but sports a 2.4GHz Core 2 Duo processor , an ATI Radeon HD 2600 PRO card with 256 MB GDDR3 retention , and a 320 GB grueling drive . The $ 1,799 iMac is a 24 - inch translation of the mid - stratum organization , with the same processor , graphics , and storage specs . ( There ’s a 2.8GHz Core 2 Extreme C.P.U. available as a build up - to - orderliness option for the 24 - in iMac — we’ll feature its benchmarks in a succeeding clause . ) All embark iMacs support up to 4 GB of RAM .

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Speedmark 4.5 scores are relative to those of a 1.25GHz Mac mini, which is assigned a score of 100. Adobe Photoshop, Cinema 4D XL, iMovie, iTunes, and Finder scores are in minutes:seconds. All systems were running Mac OS X 10.4.10 with 1GB of RAM, with processor performance set to Highest in the Energy Saver preference pane when applicable. The Photoshop Suite test is a set of 14 scripted tasks using a 50MB file. Photoshop’s memory was set to 70 percent and History was set to Minimum. We recorded how long it took to render a scene in Cinema 4D XL. We used Compressor to encode a 6minute:26second DV file using the DVD: Fastest Encode 120 minutes – 4:3 setting, using Apple’s qmaster software to create a two instance cluster to process the job. In iMovie, we applied the Aged video effect to a 1-minute movie. We converted 45 minutes of AAC audio files to MP3 using iTunes’ High Quality setting. We used Unreal Tournament 2004’s Antalus Botmatch average-frames-per-second score; we tested at a resolution of 1,024 by 768 pixels at the Maximum setting with both audio and graphics enabled. We created a Zip archive in the Finder from a 1GB folder. To compare Speedmark 4.5 scores for various Mac systems, visit our Apple Hardware Guide .—MACWORLD LAB TESTING BY JAMES GALBRAITH, JERRY JUNG, AND BLAIR HANLEY FRANK.

The iMac

The previous generation of iMacs released about a yr ago number in four received configurations , in 17- , 20- , and 24 - inch enclosures . Processor speeds browse from 1.83GHz to 2.16GHz , with a frontside bus topology of 667MHz . ( The frontside bus on the new line of iMacs is 800MHz . ) For the use of this tryout , we ’ll focus on the former 24 - inch model , which romp a 2.16GHz processor .

Our bench mark tests find the two new 2.4GHz iMacs to performing nearly identically — hardly surprising since the only difference between the two models is the display size . The new 2.4GHz machines were quicker across the board than the sure-enough top of the business 24 - inch 2.16 GHz iMac , with a 9 - percent melioration in Speedmark score . The only test where the old car come out on top was in our Unreal Tournament psychometric test , in which it managed to display a couple of extra frames per second . As games are for the most part dependent on the graphics placard , it appears that the older Nvidia GeForce 7300GT held its own , despite make half the amount of video recording random-access memory as the new ATI offer . We ’ll run a few more game trial run and will post the results on Macworld.com as soon as we have them .

Aluminum iMac Benchmarks

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Speedmark 4.5 scores are relative to those of a 1.25GHz Mac miniskirt , which is assign a score of 100 . Adobe Photoshop , Cinema 4D XL , iMovie , iTunes , and Finder scads are in minutes : seconds . All systems were running Mac OS disco biscuit 10.4.10 with 1 GB of RAM , with C.P.U. performance adjust to Highest in the Energy Saver preference pane when applicable . The Photoshop Suite test is a set of 14 scripted tasks using a 50 MB file . Photoshop ’s memory board was determine to 70 per centum and History was set to Minimum . We recorded how long it took to render a scene in Cinema 4D XL . We used Compressor to encode a 6minute:26second DV file using the DVD : Fastest Encode 120 minutes – 4:3 setting , using Apple ’s qmaster software to make a two example cluster to process the job . In iMovie , we applied the Aged telecasting effect to a 1 - minute motion-picture show . We exchange 45 minutes of AAC audio files to MP3 using iTunes ’ High Quality setting . We used Unreal Tournament 2004 ’s Antalus Botmatch mediocre - frames - per - minute grievance ; we tested at a resolve of 1,024 by 768 picture element at the Maximum setting with both sound recording and graphics enabled . We created a Zip archive in the Finder from a 1 GB brochure . To equate Speedmark 4.5 scores for various Mac system , visit our Apple Hardware Guide .—MACWORLD LAB examination BY JAMES GALBRAITH , JERRY JUNG , AND BLAIR HANLEY FRANK .

Looking at the numbers racket , the new 2GHz 20 - inch iMac turned in an impressive performance stack up against the marginally faster 2.16GHz processor in the older machine . That speed advantage helped the old iMacs sharpness past the raw 2GHz model in some tests , but the new downcast - end iMac actually poke past the older framework by one point in our Speedmark entourage thanks to a bouncing Photoshop score , faster startup time , and better carrying out when unzipping turgid files .

But masses determine whether to raise to this iMac probably are not making the jump from the machines give up a year ago ; rather , they ’re making the jump from older models , including PowerPC - establish hardware . That ’s why we included a 2.1GHz iMac G5 here as a reference point . represent the top of the line in the last multiplication of pre - Intel iMacs , this system cost $ 1,699 when launch , and its grudge demonstrate the iMac ’s advance in the last 22 months . Comparing Speedmark scores , the new top of line iMac turned in a 43 - percentage fast Speedmark score . In some mainframe intensive tests , the new iMacs finished in less than half the time it claim for the G5 example . The novel 2GHz iMac was 32 - pct quicker in Speedmark .

Our build - to - order iMac with the 2.8GHz Core 2 Extreme is on parliamentary law . appear for those final result — and a review of the updated iMac line — before long .

[ James Galbraith is Macworld science lab director . ]