PASADENA, Calif. — The only time that actress Mackenzie Davis was spanked as a child was when she wrote a bad word on the sidewalk in foot-high block letters. She was 5.

To this day she doesn’t know where she heard it, how she knew to spell it and why she wrote it. But that old impish streak is still with her. And while she now calls it an “independent” spirit, it’s stood her in surprisingly good stead.

Costarring in AMC’s infectious drama “Halt and Catch Fire,” she plays a fiery computer whiz who infiltrates the burgeoning computer world at precisely the right time. The show, which is in its second season, takes place in the early ’80s in the infancy of computer science. “Halt and Catch Fire” is a programmer’s term for a computer that’s gone goofy and needs rebooting.

Davis, who grew up in Vancouver, says she erupted from her mother’s womb knowing she would be an actress. But she had promises to keep first.

“My parents were supportive. I think it was very important to them that I got my education before I went full-throttle into acting, so they said I should go to university first, and I did. And studied — not acting — which I think was a very good choice to sort of not isolate yourself too much on one field. I studied English literature and women’s studies. I never thought of it as something I was GOING to do. I always knew I was going to be an actor,” she says in the sunny patio of a hotel restaurant.

After college in Montreal she moved to New York to try her luck. She was frightened of the prospect because she was leaving her friends, she says. “But I wasn’t 18, I was 22, and I had lived other places by myself before that, so I wasn’t scared.”

After university she studied at the Neighborhood Playhouse for two years and took some time off to stay in her uncle’s place in London, then on to Paris for four months. “I think the idea of being 20 and living in Paris by yourself sounded very romantic to me, but the reality of it was a lot lonelier than I had expected, but it was interesting,” says Davis, who’s wearing a white top, a leather jacket with her spiky blonde hair grown out, grazing her cheek.

To make ends meet, she tried modeling. “I hated it just because you don’t have a voice in modeling,” she says, glancing down at her hand which is adorned with a ring made of her wisdom tooth.

“People sort of talk at you and about you, but never TO you. I always like being part of the conversation, not just the object of the conversation,” she says.

In New York she wangled a couple of jobs under-the-table because she didn’t have a work visa. “So I worked at this theater company that also had a bar in it and you sort of performed in the bar — like a gangster’s moll. I worked in this café in the lower east side with this horrific boss. Waitressing was very fun. I really liked chatting with people as a waitress, but I wasn’t 100 percent reliable at getting the orders right — which may have been why I got fired,” she laughs.

The downtime came when she realized she was a late-bloomer. “I was 24 and that’s very old for an actress to have never worked, and to have just been in school,” she says. “That was my perception that there’s a real timeline on actresses. I’d always had such faith that everything was going to work out and just wasn’t anxious about things, and suddenly I graduated from this little theater school, and I was 24. I was like, ‘I don’t have a plan or an agent, never had a job, don’t know why anyone would hire me. I don’t know.’ I just really panicked and freaked out. The summer before I started working was a dark patch.”

But the dark patch faded when she landed her first job — a movie called “Breathe In” with Amy Ryan, Guy Pearce and Felicity Jones. “It was just the best first experience you could have and allowed me to start working, and I was just flipping the pages of ‘Backstage’ before that — so it was really very lucky … I was newbie lucky and it’s not lost on me,” she nods.

Davis, who claims she lacks self-control, is determined to take more command.

“I’d like to be a little bit more diligent with myself about writing stuff and being disciplined in that way. I can be very casual and laissez faire about things: What will happen, will happen. We’ll just see what next opportunity comes. But I think I’d like to be a little more instrumental,” she says.

“I’ve always believed in fate, and it’s been OK. But I think I should put more of an onus on myself more, especially creatively.”