But fans and investors who had been hoping that the Apple chief executive would pull some new breakthrough in hardware design out of his hat during his Macworld Expo keynote came away empty-handed.

Apple CEO Steve Jobs

The Mac rumor sites had been rife with speculation that Jobs might use the New York edition of the semiannual trade show to roll out a successor to Apple’s most popular model, the iMac.

The curvy, colorful consumer machine has had a series of updates but no major redesign since it was introduced three years ago, and sales have slowed.

But no changes to the all-in-one iMac — not even new colors — were announced. In fact, Apple seems to have taken a slightly conservative turn: gone are the tie-dye like Flower Power and Blue Dalmatian plastics introduced in February.

Instead, the three new models introduced will come in relatively staid colors used in some previous versions: indigo, snow and graphite.

All three new configurations, however, feature faster processors, more memory and bigger hard drives. Each now has enough built-in memory to run Mac OS X. Previously, only the $1,499 version met the new OS’ 128-MB minimum requirement. And all three iMacs now have drives that can write as well as read CDs — a capability previously missing from the entry-level iMac.

Apple is also backing away from price competition with low-end PCs: It set the price of its new base model at $999. That is $100 more than the previous entry-level model and $200 more than the stripped-down base model offered last fall.

Said analyst David Bailey of Gerard, Klauer Mattison: “Apple seems primarily focused on accelerating the upgrade cycle among its current customers, and enticing new users isn’t as important to them this year. There isn’t as much price sensitivity among people already committed to the platform."

Previously, a 733-MHz G4 ran Apple’s fastest single-processor professional model, and cost $2,999. Now, the same chip powers the $1,699 base configuration.

The midrange Power Mac G4, priced at $2,499, jumps to 867 MHz, and it will now come with a SuperDrive that can read and write digital video discs as well as CDs — a drive previously available only in a $2,999 Power Mac.

A new high-end Power Mac configuration, due next month and priced at $3,499, will include the SuperDrive, dual 800-MHz G4 processors and an Nvidia graphics card that can drive two monitors.

With Intel’s Pentium 4 now offering roughly twice the clock speed of the G4 chips, Jobs called on Jon Rubinstein, Apple’s senior vice president of hardware engineering, to present a technical analysis refuting what he called the “megahertz myth” — the common assumption that higher frequency always means faster performance.

Probably more convincing to most of the expo audience, however, was a performance “shoot-out” in which Jobs pitted the 867-MHz Mac against a Windows PC with a 1.7-GHz Pentium. Despite its slower clock speed, the Mac outperformed the PC by up to 80 percent in a series of operations in two widely used professional graphics applications, Adobe Photoshop and Media 100’s Media Cleaner Pro.

Analyst Chris Le Tocq of Guernsey Research said the enhancements add up to “a fairly serious power uptick, the kind of horsepower the professional graphics people always appreciate.”

During his presentation, Jobs did show “10 on X,” featuring new versions of such major applications as Microsoft Office, Adobe Illustrator and QuarkXPress optimized for Mac OS X. But most of these programs were still in the “coming soon” category, in most cases with no date set.

Jobs also offered a sneak peek at Mac OS X Version 10.1, an upgrade scheduled to ship in September. Its key enhancement, he said, is “performance, performance, performance.” In particular, launching applications, opening new windows and pulling down menus — operations that are sometimes sluggish on the current version — will be significantly speeded up.

The update will also be the first to support DVD playback.

Jobs said Version 10.1 will be free to users of Mac OS X, which is now included with all new Macs. But the upgrade, which will fill 550 MB, won’t be available for downloading, so customers will have to pay a $20 shipping and handling charge to get it on CD-ROM.

In September Apple will also upgrade iDVD, the software that enables users to design DVDs on Power Macs equipped with its SuperDrive. That update, which Jobs said will deliver “production values as good as or even better than you see in Hollywood DVDs,” will also be available only on a $20 CD.