With the iMac G5, Apple has pared the desktop computer down to little more than the parts that people look at and touch -- keyboard, screen and mouse.

Where the now-discontinued iMac G4 consisted of an LCD attached by a metal arm to a hemispherical base, the new iMac is all screen. Every internal component, from the DVD drive to the power adapter, has been fitted into the back of the display, which pivots slightly atop a "foot" made from a single slab of aluminum.

Unlike all-in-one PCs from Gateway and Sony that also combine screen and computer in one housing, the iMac G5 doesn't look like a hunchbacked monitor: It's only about two inches thick. The power button and two FireWire and three USB 2.0 ports reside on the back, leaving a front that consists of just the LCD and a chinlike expanse of white plastic below it that hides the power adapter and speakers.

This machine looks as different from the iMac G4 as that model did from the original, bulbous iMac G3. But it shares its ancestors' design goal -- to be a desktop that takes up as little desk as possible. The iMac G5 has the smallest footprint of any Mac, or, for that matter, any desktop I've ever come across. With the $99 option of a kit that adds a Bluetooth wireless receiver and a wireless keyboard and mouse, it doesn't even dirty the desk with extra wires. Any smaller, it would be a laptop.

But unlike any laptop Apple makes, the new iMac runs on the same G5 line of processors as its Power Mac and Xserve machines while costing a lot less, from $1,299 to $1,899 before any options.

That's an appealing pitch for computer users who don't want a hulking tower-case desktop invading their personal space, but who also don't want to sacrifice the comfort of a bigger screen, full-size keyboard and separate mouse. After testing a mid-range iMac G5 last week, I think Apple has delivered on that promise -- with one glaring exception.

That's the default allocation of memory, just 256 megabytes in each of three standard configurations ($1,299 for a 17-inch display, 1.6-GHz G5 processor, 80-gigabyte hard drive and DVD-ROM/CD-RW drive; $1,499 for a 17-inch display, 1.8-GHz G5, 80-GB hard drive, DVD-RW/CD-RW drive; $1,899 for a 20-inch display, 1.8-GHz G5, 160-GB hard drive, DVD-RW/CD-RW drive).

The 17-inch, 1.8-GHz model I used came with 512 megabytes onboard, but when I removed one memory module to see how it ran with a normal allocation, the results were just this side of miserable anytime I had more than a few programs running. Songs in iTunes stuttered if I manipulated an image in iPhoto at the same time, Microsoft Word 2004 took a painfully long time to launch, and switching between programs sometimes entailed lengthy pauses.

Combining a high-powered G5 processor with only 256 megabytes of memory is cruel and unusual computing. Apple should bump the minimum up to 512.

The DVD-RW SuperDrive that came in the tested model, with CD- and DVD-write speeds well behind those of DVD+RW drives in other desktops, constituted another brake on the iMac's performance.

In daily use, the G5's extra speed wasn't even that easy to notice sometimes. As a whole, the computer felt distinctly snappy compared with a two-year-old iMac G4. But when I timed basic iPhototasks, the G5 took only a few seconds less than the G4 did. The benefit's bigger with processor-intensive chores such as video editing.

Apple assembled a fairly crafty system to keep this processor from overheating. The iMac's three cooling fans are whisper-quiet when the machine is at rest, but as you put the processor to work, they will rev up, then gently decelerate when computing activity abates.

This noise doesn't get bothersome until you start to max out the processor, at which point a sustained whine emanates from the machine.

If you open the iMac's case -- just loosen three screws and slide off the back panel -- you can eyeball its layout of fans and cooling ducts, plus a novel advantage for an iMac: components you can replace yourself. Previous iMacs were packaged like appliances, with no user-serviceable parts beyond the memory and wireless-card slots. Here, the hard drive and other components can be replaced and, in some cases, upgraded at home.

The iMac G5 packs Apple's usual bundle of its thus-far virus-, spyware- and worm-free Mac OS X operating system; its outstanding iLife suite of music, photo and video software; and a mediocre set of productivity applications (AppleWorks is woefully antiquated, and Intuit's Quicken 2004 has already been replaced by Quicken 2005).

There's also one amazing extra, a setup utility that automatically moves your data, settings and even programs from any old Mac with a FireWire port and Mac OS X. Start up this program, connect your computers with a FireWire cable, reboot the old machine, confirm what files it will transfer, then sit back and watch. This data transfusion took about an hour -- not bad for a perfect transfer of everything I'd done over the past 21/2 years. The Windows world has nothing equivalent to this.

On the other hand, the Windows world offers many less costly desktops. Apple is overdue to offer a cheap, compact desktop without a built-in monitor; without that, it has no answer to the quite capable $500-and-less systems available.

For now, Apple has chosen to play in the higher end of the market, and it has done so with its usual style and elegance. It has thought seriously about how desktop computers can stay relevant in an increasingly laptop-centric market, and the result is one of the only desktop computers worth talking about.

Living with technology, or trying to? E-mail Rob Pegoraro at rob@twp.com.

Apple's iMac G5: a two-inch-thick all-screen PC almost small enough to be a laptop.