Apple Chief Executive Steve Jobs unveiled three new iMacs during his keynote address on Wednesday at Macworld Expo. Jobs introduced a 500MHz iMac, with 128MB of RAM and a 20GB hard drive, for $999. He touted another model running at 600MHz, with 256MB of RAM and a 40GB hard drive for $1,299. These first two models are available now. The third model, available in September, will run at 700MHz, with 256MB of RAM and a 60GB hard drive for $1,499. Each of the new models will include a CD-RW drive. What Jobs didn't announce -- a much-anticipated, flat-panel iMac -- grabbed analysts' attention. Many analysts were hoping Jobs would introduce a new iMac model during his keynote speech. Chief financial officer Fred Anderson said the company's fourth-quarter earnings and revenue would be slightly higher than its third-quarter results, a bit below expectations. Meanwhile, analysts said Apple's outlook was largely due to an aging iMac line. In response to that outlook, many analysts slightly lowered their earnings targets and reiterated their previous ratings. Goldman Sachs analyst Joe Moore speculated that Apple's aging iMac product line was the reason the company's outlook wasn't better. He said Apple watchers were hoping that Jobs would unveil a new iMac with his keynote speech, but he didn't deliver. "It seems that the bulk of the shortfall in September is coming from the iMac lineup," said Moore, who said Apple's flat-panel iMac may not be ready. Moore wasn't alone with that theory. "We believe Apple will be challenged in its fiscal fourth quarter without a major revision to its iMac consumer desktop, given the paucity of PC demand," said Gerard Klauer Mattison analyst David Bailey. "It is hard to pin the company down given the secrecy around new products, but we know management is aware that the iMac family is getting long in the tooth," said Moore. "We think that it is important to get the product out and do not expect them to wait until the next Macworld." Shares of Apple were off $4.17, or more than 16 percent, to $20.93 in early trading. Jobs also introduced three faster Power Macs, with an entry-level model running at 733MHz, as well as a 867MHz model. The third model has two 800MHz chips. The 733MHz Power Mac, which sells for $1,699, includes 120MB of memory, a 40GB hard drive and a CD-RW drive. The 867MHz version, priced at $2,499, includes 120MB of RAM, a 60GB hard drive and a SuperDrive, which reads and writes both DVDs and CDs. The high-end machine, which comes with two 800MHz chips, sells for $3,499 and comes with 256MB of memory and an 80GB hard drive. All three new Power Macs will also sport a new silver-colored case, Jobs said. The high-end model will be available next month, and the other two models are available now, Jobs said. Jobs used the early part of his keynote address to focus on Mac OS X, the new operating system from Apple. Jobs offered a preview of Mac OS X 10.1, which he said would ship in September and offer support for playing DVD movies, along with new networking features and improved handling of digital photos. Jobs also promised faster launching of applications, resizing of windows and other performance enhancements. "You name it, it's faster," said Jobs, who appeared in his now-trademark blue jeans and mock turtleneck. Jobs also announced that the company plans to open four more retail stores next month at malls in Minnesota, Chicago, Boston and Dallas. "We think they are a great complement to the other great retailers we have out there," Jobs said. Aiming to demonstrate support for the new Mac operating system, Jobs showed off 10 programs under development for OS X, led by Microsoft's Office business-application software, due to be released this fall. News.com's Sandeep Junnarkar and staff writer Larry Dignan contributed to this report. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet news forum. Let the editors know what you think in the Mailroom. And read other letters.