I am currently in grad school in the UK in the area of computer science. Our phd model is as follows:
Year One: Intro, get your head around things
Year TWO: Work
Year three: Work
Year four: Writeup

The topic, etc are all up to you ... very much a "sink or swim" approach. People get around by forming peer review groups and generally talking to one another/others...

I was wondering what other models out there exist?

the model I know has the same content as yours but compressed into three years. In fact, the registration period is three years including writing up, any need for a fourth year needs to be justified in front of the head of school and may or may not be granted. Never heard of anybody being granted a fourth year here in this place.

Same here Jouri - we're allowed a fourth term (but not funded) and that's it. Otherwise the major factor affecting the model is whether or not your project is part of a larger group project.

the one I am on is much more fixed, proposal in 4-8 months after registration, transfer to PhD after a year - 2years part time, when you have to have 2 chapters ready, then finished thing 3-3.5 years or up to 6-6.5 if part time. The first bit is where I'm at at the moment, altohugh I'm waiting on my supervisor to get back with info onthe ethics bit which I have sent. The thing is I virtually had to complete this stage before I could even register - area is a bit, no, very, controversial so they needed not the usual 2 sides, but 18 pages of information, and a rewording so they didn't quite get what the thing would really be about