Apple Computer's Mac OS X launch shook the earth for many of the company's die-hard fans last weekend. But aftershocks may cause some Mac enthusiasts unexpected trouble. Retailers and initial buyers report strong enthusiasm for the new operating system, which Apple started selling Saturday. But limited hardware support and a potentially flawed firmware upgrade could sour some people's first experiences with Apple's first complete overhaul of its OS since its 1984 introduction. Apple fans rushed stores starting at midnight Saturday for early copies of Mac OS X. Ten stores chosen randomly across the US sold out every copy of Mac OS X on Saturday and were expecting new copies to arrive by the end of this week. An employee for Rec-Mac Computer in Mesa, Arizona, compared the frenzy to "people waiting in line to get concert tickets". European sales were also reportedly strong, with computer shops in London's Tottenham Court Road and elsewhere making brisk OS X sales, according to Apple. Dan White, a Unix developer in Maryland, is among the Mac enthusiasts who have already picked up a copy of the new operating system. "I'm tickled pink about it," he said. "I've been doing Unix software development for years and years now, and when I heard Mac was going Unix, I thought, 'Yes!'" Tim Deal, a Technology Business Research analyst, said White is not alone. "The release of OS X has certainly been met with great fanfare, and it appears that Apple's loyal following is wasting no time in buying a copy." But little hiccups with how the new OS handles hardware -- either in Mac OS X or in "Classic" mode -- leaves some people stumped. Classic refers to Apple's Mac OS 9.1 environment for running older programs on the new operating system. Ted Landau, a college professor and Web master for MacFixIt, said the number of support issues "are about what I expected. There haven't been many universal problems. That's a good sign. "Most of the emails I get are about problems that are not true for all users -- sometimes true for several users but certainly not everybody. There's nothing that makes me want to post a topic with the headline: 'Beware of Mac OS X.' There are no showstoppers here." Common problems include connections to SCSI devices and external hardware from Classic mode, something Apple had prepared people for. In addition, many Mac OS X owners must reboot back to Mac OS 9.1 to use America Online. But Ron Logee, a software consultant in Arlington, Virginia, who is already using OS X, noted that writing down the Internet settings when launching Mac OS X for the first time and using that information to set up America Online resolves the connection problem. "I'm using AOL in Classic mode, and everybody I know is using it in Classic mode," he said. Hardware issues Mac OS X's biggest problems are with hardware. Like Unix or Windows 2000, Mac OS X limits software's direct access to hardware, forcing it to go through the operating system instead. For hardware manufacturers, and even Apple, this has created some problems. For example, Apple had to ship Mac OS X without full support for CD-rewritable, DVD and DVD-recordable -- optical drives the company has shipped on its systems. That support is expected to start next month, with the addition of CD-RW capability followed by DVD playback and DVD recording by summer. For now, people must reboot back to Mac OS 9.1 to use these drives. "The only particular hardware I need to deal with on a regular basis is a CD burner," White said. "I certainly have no trouble booting back to use it." Apple also faces challenges because Mac OS X is just so different from its predecessors. The new operating system, which is based on Unix, boasts better memory management and greater stability than older Mac OS versions. "This situation here is a classic case of growing pains," Gartner analyst Neil MacDonald said. "You have a relatively major overhaul in architecture, and it takes awhile for the hardware to catch up. For Apple, Microsoft, or even Linux for that matter, some of this has to come through trial by fire." Although Microsoft launched Windows 2000 with support for a lot of hardware, the company did not execute as well with Windows NT 4, MacDonald said. "If you go back in history and look at exactly why NT 4 didn't take off on the desktop, it didn't have the hardware support for the types of things you needed like CD-ROM drives at the time and many graphics cards." As Microsoft sorted this problem out over time, Apple likely will do the same, MacDonald noted. One reason Apple has pushed back offering Mac OS X on new computers until summer is the hardware support issue, say analysts. Besides the absence of support for optical drives -- both Apple and third-party models -- Mac OS X stumbles in other areas. Owners of the popular subwoofer iSub, which works with iMac and Power Macs introduced in January, will find it does not function under Mac OS X. In another interesting twist, Mac OS X works with many external USB floppy drives, but not internal drives found on older Mac models such as the Power Mac Desktop G3, Power Mac All in One, and PowerBook G3. "You can't expect the world here in terms of the hardware," noted Logee, who is running Mac OS X as his main operating system. "When I started installing it, it brought a smile to my face, and I've been smiling ever since." Memory glitches In some ways, Apple's biggest technical issue right now is only peripherally related to Mac OS X. In preparation for the new operating system's release, Apple on 23 March issued a series of firmware upgrades for many Macs. Firmware stores settings and instructions that hardware uses independent of the operating system. But after installing the firmware, a fairly large number of people reported their systems no longer recognise all installed memory. Apple declined to comment about the problem, but several sources outside the company familiar with the glitch said new firmware will be released soon. Logee said he hasn't applied the new firmware and will wait for Apple's updated version. MicroDesign Resources analyst Peter Glaskowsky faulted Apple for the problem. "The quality of the memory is not likely the issue. This is a bad thing from the standpoint of Apple's testing its firmware upgrades," he said. Because Apple has not yet communicated anything about the problem, Glaskowsky said he could only speculate about its nature. "It is something probably related to the speed ranges they allow. It would be my guess they have disallowed some speed combinations or they may have decided there's a mismatch between the DIMMs and were not going to let it run." Gartner's MacDonald also said all he could do was speculate, but he cut Apple more slack. "It sounds like a timing issue with the software, where you have some type of clone memory that is not quite up to the spec Apple was counting on. You get a mismatch, and things don't work." Whatever its cause, because the memory is likely undamaged by the firmware upgrade, updated firmware should correct the problem, Glaskowsky said. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet news forum. Mac OS X 10.0 has arrived, and Stephen Somogyi's prognostications have largely come to pass. He understands Apple's need to ship OS X, but this new OS definitely seems a bit underdone. The reports of kernel panics, unexpectedly low performance, and other manifestations of .0 malaise are many. While this was to be expected to some degree, it was also avoidable. Go to AnchorDesk UK for the news comment. Let the editors know what you think in the Mailroom. And read other letters.