Steve Smith is "like a computer" when he is batting, Steve Waugh said after the Australia star scored another Ashes century.

Smith made his second century of the first Test against England at Edgbaston, putting the tourists in a winning position on day four on Sunday.

The right-hander, playing his first Test since his ball-tampering ban, made 142 in the second innings, having rescued his team with 144 in the first.

Smith became the first Australian to score two centuries in the same Test in England since Waugh in 1997.

Waugh, a mentor with the Australia team in England, lauded Smith's approach and said the 30-year-old seemed to have answers for whatever opposition sides threw at him.

"His preparation is amazing. He's thorough, he hits more balls than I've ever seen anyone [hit]," former Australia captain Waugh told Channel Nine on Sunday.

"When he goes out to bat it's almost like he's in a trance-like state. He knows exactly what he wants to do.

"He knows the opposition, what they're trying to do, how they're trying to get him out and he seems to have an answer for everything.

"He's an incredible player. I don't think I've ever seen anyone quite like him and his appetite for runs is second to none. His technique is amazing, it's unique, but he knows what he's doing, he knows how to score runs.

"It's like he analyses every ball, and it's like a computer – he spits out the answer."

England will resume day five at 13-0, needing another 385 runs for victory in a Test they are more likely set to look to save.