Feb. 18, 1981 was the day Bob Petrella met his friend Susan Angelo.
"It was a Wednesday," he said.
He remembers. She doesn't.
In 1976, Petrella met his friend Tom Challis.
"I remember the first time we really talked, though, was New Year's Day 1978 when we watched Oakland and Denver," Petrella said. "It was over at Patty's house."
For the average person, the ability to recall the odd date -- a birthday, anniversary or reunion -- might not be that impressive. But Petrella has a different gift. He remembers almost everything.
Petrella, 58, is only the fourth person in the United States discovered to have what has been described as a super-autobiographical memory. Give him a date or event and he's likely to remember it. Sometimes he remembers more about his friends' lives than they remember about their own.
"He called me, I swear, six years after I had met him," said Angelo. "I got a telephone message from him one day. He said happy anniversary, we met six years ago today."
"This guy's from another planet," said Challis. "Like '74 ... when Nixon was impeached, I think about ... graduating from high school. This guy, he remembers [that] it hailed one day in July or something that same year."
"It's Thursday when [Nixon] announced it," Patrella said.
"See what I'm saying," said Challis.
Petrella lives a fairly normal life, working in Los Angeles as a producer for the Tennis Channel on cable television. Some people who have known him for years are still stunned by his memory.
The day Princess Diana was killed?
"That was a Saturday and it was Aug. 30, 1997," he said. "I just remember sitting at home and turning [on] CNN or whatever. It was all over the news ... and then the next day the Steelers lost to Dallas, 37-7, which was Aug. 31."
March 30, 1981?
"Reagan was shot, and that night Indiana beat North Carolina for the NCAA championship. Isaiah Thomas played for Indiana and James Worthy and Sam Parkins played for North Carolina. It was a year before Michael Jordan joined the team."
Aug. 15, 1969?
"That was Woodstock. That was a Friday," he said.
Petrella's memory is a mixture of personal experiences and verifiable public events. He leans toward sports, but historical dates are embedded in his brain as well.
It's a mystery how he does it.
"We don't know how it works, and we would like to know how it works," said Dr. James McGaugh, the founding director of the Center for the Neurobiology of Learning and Memory at the University of California, Irvine.
Petrella and the three others with super memory have been the subjects of study at the center.
"These are not learning machines. These are not people with so-called photographic memory," said McGaugh. "These are people who learn certain things about their lives and don't forget."
The doctors have screened about 2,000 people with 60 questions that only those with super memory have a chance of answering.
"I always explain to people [that it's] like I'm walking around with a video camera on my shoulder and every day is a videotape," Price told ABC News last year. "So if you throw a date out at me, it's as if I pulled the videotape out, put it in the VCR and just watched the day as it happened, like from my point of view."