Apple’s skinnier iMac is a beautiful beast

Desktop computers aren’t the sexiest of product categories these days, but the all-in-one iMac largely defies the trend. Apple has continued to refine it inside and out, with a beautiful new slimmed-down design and a few new technological tricks as well.

The iMac comes in two configurations, one with a 21.5-inch screen starting at $1,299, the other a 27-inch for $1,799. More than size and price set them apart.

While both come with eight gigabytes of memory, the larger one allows you to expand it to as much as 32 GB. The smaller model, in a throwback to the earliest days of Mac computing almost 30 years ago, isn’t user-expandable. If you want more memory (up to 16 GB), Apple has to do it for you.

From the front, the new iMacs look a lot like the models they’re replacing. But the story changes when you look at them sideways.

Where the previous models were about an inch thick, including a slot for the DVD drive, the new one has a bowed back that tapers at the edges to a mere one-fifth of an inch.

And don’t bother hunting for the DVD drive. As on the most recent MacBook Pro models, Apple has done away with it, arguing that the rise of streaming media and downloadable applications and content have rendered it obsolete. For those who disagree, it’s $79 extra for Apple’s external SuperDrive.

Unlike the latest MacBooks, the iMac lacks Apple’s ultra- high-resolution Retina display. Still, it has pleasures of its own.

The biggest one is that, despite the screen’s glossy finish, it is noticeably less reflective than its predecessor — a 75 percent reduction, according to the company.

That’s largely a product of the same manufacturing changes that allow it to be so thin. Apple says it has shrunk the gap between glass and display, resulting in less glare without sacrificing image quality.

All the redesigning has an indirect benefit as well: While no one would call either iMac portable, they are eight and 9.5 pounds lighter than the models they replace.

Both iMacs come with a generous one terabyte of hard-disk storage standard, with three terabytes available as an option. And if you’re willing to spend from $250 to $400 more, things get interesting.

With these models, Apple is introducing an option called Fusion Drive, which is a conventional hard disk seamlessly combined with 128 gigabytes of flash storage.

Other computers have used lesser quantities of flash, which is both much faster and much more expensive than hard-disk space, to speed boot-up and temporarily store files while they’re in use. Apple, though, is using the greater amount of available flash to permanently store often-used programs and files.

The result is performance that is much zippier, even though the hard disk it’s married to in the 21.5-inch model spins at 5400 revolutions per minute, not the 7200 RPM more often found in premium desktops and laptops.

Equipped with a Fusion Drive, the 27-inch iMac booted in under 15 seconds while a 2.3-gigabyte file loaded in less than five. Apple says that imports and file-copying are up to 3.5 times faster than a 7200 RPM conventional drive.

Both iMacs are powered by Intel’s latest “Ivy Bridge” generation of quad-core processors — the i5 is standard, while an i7 is available as another extra-cost upgrade — and graphics chips from Nvidia. Both also include four USB 3.0 ports, two high-speed Thunderbolt ports and a slot for an SD card.

You have a choice of pointing devices, either Apple’s Magic Mouse or Magic Trackpad. Since the arrival of the Lion version of the Mac operating system last year, I’ve preferred the trackpad.

With the rise of laptops, tablets and smartphones, the desktop computer is, let’s face it, something of a dinosaur. And at a price that with a few options can easily exceed $2,500, the iMac should by rights be dead on arrival.

But it isn’t: Once again, Apple writes its own rules in the marketplace.