Is your Roomba a boy or a girl?

The Roomba, of course, is that clever little house-cleaning robot. I reviewed Roomba in October 2002, then bought my own a few months later. Since then it's been happily sweeping my living room and dining room every week or so. It also terrifies my cats and my three-year-old twin boys. All well and good-but what's the Roomba's gender?

"It's a girl," says my wife. "It's round. It's close to the floor. It ends with an a'. I always think of it as a wom-ba.'"

But if the Roomba is a girl, then Asimo is definitely a boy. Developed by Honda Motor, Asimo is a humanoid robot that walks around like a short astronaut in a white space suit. Four-foot tall Asimo is the latest in a long line of the company's bipedal robots. These days Asimo spends his time as Honda's goodwill ambassador to the world's science museums, auto shows, and other venues. Last month he was spotted in Hanoi, Vietnam.

Asimo doesn't look especially boy-like-there's no slingshot in his back pocket, there's no telltale bulge under his belt, and there's no hint of facial hair. In fact, you can't even see his face: the robot's head is covered with a visor that has just two big holes for its video-camera eyes. But Honda repeatedly refers to the robot with the pronoun "he" on the Asimo website.

Indeed, Honda has taken great pains to make its walking robots more lifelike, and part of that realism appears to include giving the robot a friendly sounding name (the previous generation was called simply "P3"). The company's earliest attempts at walkers were really nothing more than a pair of legs and feet with a big box on top of them. But over the years the robot forms have become decidedly more human-and more male.

Whether or not you think that gender belongs in our mechanical creations has a lot to do with your vision of how these creatures will fit into our future. It certainly takes more effort to make a robot that's gendered than one that's asexual. But engineers just want to have fun. Building gender into robots might be a way for the robots' designers to express their own playfulness and creativity.

Dig a little deeper, though, and you'll discover another reason why gender might be a good thing for our robot servants: gender will make robots more compatible with their human masters.

As human beings, we constantly try to layer emotions, desires, and other human qualities onto our machines. Computers aren't aware of the emotional traits that we assign to them, of course. We might say "the computer ate my file because it's having a bad day" because we lack a better explanation for what's happening inside the system's microprocessor (its "brain.") Yes, there have been attempts to develop synthetic emotions for machines, but that's all artifice. Most people realize that fundamentally there's nothing going on inside the silicon except the cold calculation of ones and zeros.

Still, if you are interested in building an effective interface between humans and computers, you might just be better off creating a machine that projects a simulated emotional response. Because human beings are hard-wired for emotions, we might find it easier to work with such machines-especially if these machines were sharing our physical surroundings, rather than being good little drones on the factory floor or up on Mars.