I'm used to a computer that slows down over time. For the first time in recent memory, I've been testing a computer that actually speeds up.

Over the past week, I've tested the new Apple iMac 21.5-inch, the model with a super-thin .19-inch bezel. To give you an idea of the thickness, the iMac is about the same thickness as the new iPhone 5, although the back of the computer bows out toward the stand. Apple says the design is 40 percent thinner than the previous iMac.

If you're into office aesthetics, the thinner design will mean a series of desk computers scattered around your office will have a fresher, cleaner look. It's a bit like being on the set of a sci-fi movie where everyone has super-thin workstations.

Fusion Drive

My biggest surprise, though, is that the iMac actually seemed to get faster over time. This is a bit subjective--I don't have detailed benchmarks to share, and I'd be surprised if anyone does. My test iMac, priced at  $2,149, includes the Fusion Drive, which added an extra $250 to the price. (The entry-level iMac costs $1,299.)

Fusion automatically monitors what you do on the computer. Essentially, the data you use the most is housed on the faster 128GB flash drive; everything else is on a 1TB magnetic drive. As you work, the iMac analyzes your apps and files and moves the ones you use the most over to the faster flash memory automatically.

This is all behind the scenes, so I was not able to see that Photoshop, Word, or my business documents were always held in flash memory. But I noticed a major speed uptick, especially when starting apps. Photoshop opened in less than a second. There's a blink and it's open, which is amazingly helpful for getting work done.

Other Specs

The iMac has several other perks for small offices. I could see the 1920×1080 display from a wide viewing angle, so for workgroups talking about the same brochure or viewing a website under development, the iMac screen is a major aid. Apple says the display reduces reflection by 75 percent compared to earlier models.

The fast processor, running at 3.1GHz on an Intel Core i7, plus 16GB of DDR3 RAM meant the system was up to just about any challenge: I edited a video using Adobe Premier Pro, and had no problems with lag. (The only time the system ran slow: for about the first hour after FedEx left the package on my doorstep in sub-zero temperatures.)

You can cram a 3TB drive in the new iMac. There's a built-in 720 pixel Facetime camera with dual microphones for Skype calls, Bluetooth 4.0 for connecting to mice and keyboards using ultra-low power, and built-in speakers that sound crisp and loud.

Overall, this is the iMac you want for office workers who want a clean work space and plenty of power and storage. The 27-inch model, which starts at $1,799, is also a smart buy for a bit more screen real estate.

Penny pinchers might balk at the pricing, though. For those who can live without the Fusion drive and get by with Windows 8, an HP Pavilion 23-inch costs just $699 with 1TB of storage. The Dell Inspirion 20-inch costs $499. These all-in-ones are not as thin as the iMac and lack some of its best features, such as a high-res screen.

I'm agnostic about Mac versus Windows--both have their advantages. But the iMac's ability to keep running as though it's fresh out of the box, plus the crisp screen, thin design, and speedy processor make this all-in-one a good business buy.