Tron: Legacy: We're not in 2D any more, Toto…

When Sam Flynn (Garrett Hedlund) first enters "the Grid" in the new Disney film Tron: Legacy, he is taken prisoner aboard a recogniser – a sort of flying cross between the Arc de Triomphe and a car carrier – before being sent off to fight in the disc war games. For fans of the cult original, it's a pivotal moment. For a start, it's the point at which the film switches from 2D to 3D. It's also the "We're not in Kansas any more, Toto" moment, when the audience becomes fully immersed in a computer-created world. But most of all, it's the moment that truly defines how much film-making technology – particularly where computer-generated effects are concerned – has changed in 28 years.

1. Production year: 2010
2. Country: USA
3. Directors: Joseph Kosinski
4. Cast: Bruce Boxleitner, Garrett Hedlund, James Frain, Jeff Bridges, Michael Sheen, Olivia Wilde
5. More on this film

When Tron was released in 1982, the technology landscape was somewhat different to today. The internet as we know it did not exist; back then, it was used only by the military and a few academics. Home computing was still for serious geeks only – the Commodore 64 came out in January of that year and was so-called because it had an astonishing 64KB of memory (your average modern smartphone – say, the iPhone 4 – is about 1,000 times faster and has 8,000 times more memory).

Tron was truly pioneering in its day: the first film to use computer-generated backgrounds and special effects – albeit very basic vector graphics, along similar lines to popular games such as Asteroids and Battlezone. It also depicted a "world" inside a computer, in which humans could interact with programs – a scenario not used again until the Matrix trilogy.
The biggest advance that today's technology brings to Tron: Legacy is the fact that one of the main characters, Clu (short for Codified Likeness Utility), is fully computer-generated – in more ways than one. Clu is an avatar – a visual representation of programmer Kevin Flynn (Jeff Bridges) inside the computer world. And as in the original Tron, he's also played by Bridges. But this time, Clu looks like a much younger Bridges – a feat achieved with motion capture and CGI trickery.
The other big innovation, of course, is 3D – a technology that did exist back in 1982, but was technically far inferior to the digital 3D we see today in blockbusters such as Avatar. At an early screening at the Imax in London last week, the audience was left enthralled, willing prisoners of this virtual world: geek heaven.
As producer Jeffrey Silver says: "It seemed obvious that Tron, being a groundbreaking film in the 80s, had to be followed with a film equally as groundbreaking in the 21st century. If we were going to do Tron: Legacy right, we would have to push the envelope."
Tron Legacy (PG) is in cinemas on 17 December.