Acer’s new Aspire S5 is one of the first of a new generation of ultrabooks to hit store shelves. Ultrabooks are the Windows world’s version of Apple’s MacBook Air: they’re lightweight, super-thin computers running the latest power-efficient chips from Intel.

The Aspire S5 is remarkable in how it exemplifies the ultrabook concept. It’s one-third of a pound lighter than the comparable MacBook Air, and its thickest point is thinner than that on Apple’s computer. Despite that, it has a battery that’s rated to last six-and-a-half hours, just 30 minutes less than the Air, and has a faster processor and the same sized flash drive as is in the comparable Air.

I loved carrying the S5 around, if only because it is so much thinner and lighter than my work-issued laptop. Also, like all flash-drive based ultrabooks, it’s quick-starting. In my testing, I was able to start it up cold in about 20 seconds and shut it down in about 15 seconds.

One cool feature of the S5 is that it’s one of the first non-Apple computers to have a Thunderbolt port. Thunderbolt is a new, lightning-fast connection technology that can be used in place of USB or FireWire to connect peripheral devices such as hard drives.

The S5’s Thunderbolt port — as well as its HDMI and two USB ports—are tucked away inside something Acer calls MagicFlip, which hides away those ports inside the bottom of the computer, helping to keep it thin. Press a button on the keyboard, and the MagicFlip will descend, exposing those ports. It’s cool, in a geeky sort of way.

Unfortunately, the S5 has a big Achilles heel — it seems to overheat easily. In my testing, it didn’t take much for the S5 fan to kick on, and it was noisy. This happened when I was running OnLive’s streaming game service, and when the computer was trying to sync my documents with Google Drive. And it happened when all I had running was my Web browser with about a dozen tabs. This happened despite the fact that I tried to lighten the processor’s load by running plug-ins to block both ads and Adobe Flash content.

Worse, when the S5 really starts to overheat, it will open up the MagicFlip port to help it cool more efficiently. When the MagicFlip descends, it props up the back of the S5, forcing it into a different angle that can be less comfortable to use. That also amplifies the already noisy fan.

One other big downside of the S5 is cost. At $1,400, it’s priced more like an Apple product than a typical Windows notebook.

TROY WOLVERTON: Silicon Valley personal technology columnist. twolverton@mercurynews.com, @troywolv