I'm a software engineer basically but have been practicing taekwondo since 2-3 months. I just wanted to know what it takes to get a black belt?
I like Juann and Wudang Kid's answers, but lets put some perspective on this. Every person that walks, for the first time, in a dojang or dojo wants to know what it takes to become a black belt and what it takes to know all the crazy things they see on TV or in the movies. Never mind the expense of promotion and some belt-factory schools, the question's answer involves the master instructor, time, learning, dedication, discipline, and perseverance but basically boils to what you are willing to do to achieve that rank.
For most taekwondo schools, you can pretty much count on 3 to 4 years to achieve the rank of 1st Dan provided you regularly attend class, stay healthy, and are willing to continue to grow. Once a person achieves that rank, they will likely find that their training has only begun at the point. The real interest of the art is in the mastery of those skills that you learned getting to the black belt rank. You will realize that one ends up re-asking (in different ways) many of the questions that you asked as a white belt. By that point, Hollywood is out of the question or focus because you are hopefully more focused upon how you can grow in the art.
Your club/school will probably have a promotional exam every few months, or every semester if it's a university program. That's a good time to watch (even if you are not ready to test) and get a good feel for what people have to learn and how good they have to be all the way up through the ranks, including dan ranks. (For a small school, you may have dan tests only yearly or intermittently, but a big school may have people testing for black belt ranks quite frequently.)
Seeing with your own eyes how it's done in your school, and the standards they expect, will be much more valuable than any advice you'll get here, which could easily differ from practices where you are specifically training.
Also, you could, you know, just ask the black belts in your dojang how long they've been training and what it takes to get to where they are. They'll probably be happy to talk to you, and their answers will be more accurate and relevant than any you get from the internet.
I agree with the other answers about the technique varying, but wanted to add one more:
Time and dedication.
We like to say that a "black belt is a white belt who didn't quit" (this is not unique to us, it's a fairly common expression). We also talk about how when a new person enters the dojang it is impossible to tell if they will be one of the ones who sticks it out and keeps working at it.
For us, if you attend all of your classes and are there every week (and no one makes all of them every week for every belt), you are looking at around 4 years of showing up every week. That's a lot of time dedicated to simply becoming a black belt.
If you are putting in that time–especially if you are taking the time you do in class and adding an extra day of personal practice and doing your warmups every day (both of which we strongly recommend)–you have put a lot of time, energy, and effort into your art.
The "black belt" (1 dan) is an arbitrary designation–both for what it takes to get it and for what it means–so your school may have a lot of specifics that they expect to see. Many times the 1 dan barely represents base camp of the art: everything up to that point is, as one person put it for Hapkido, "how to fall and how not to kill people when practicing."
But in general, what will make you a 1 dan:
Rinse, repeat for as long as it takes.
When I tested for 1st Dan, I was asked to perform Gae Baek, which is the blackbelt pattern (kata for all the karate philistines - JK). In addition to that, I was asked to perform two additional colour belt patterns at random. In my case, Won Hyu and Hwaorang.
Then came the demonstration of breaking techniques. I was allowed to choose my own technique and decided on the inner knife-hand strike. I had to break a black and a white nylon board, which is the equivalent of six wooden boards.
After that, I had to demonstrate 10 Tae kyu techniques, which I believe is optional in the curriculum. I also had to demonstrate two real world self-defense techniques ad-hoc.
I was then asked to perform a number of jumping and combination kicks. There was a particularly dificult one called the jumping front kick. What made it dificult was that I had to jump out of an L-stance, kick with my rear leg, and land in the same position. This was to test both my hip flexibility and the strength of my core muscles (the muscles under the bellybutton, in the case of TKD).
After that, I was asked some theory, e.g. what the 5 tenets are and what they mean, as well as some history and things about why we twist the front punch or why the elbow is a good striking tool.
Lastly, I was given two semi full contact sparring matches. Semi-full in the sense that we both wore protective padding.
First, bear in mind that this will differ from dojang to dojang. Depending on your association (WTF or ITA for example) there may be a list of techniques you will have to master for each belt. If you are not affiliated with an association, your teacher will have a checklist of things he wants you to learn before each belt. Ask your teacher what the requirements will be.
Other than specific techniques, part of testing is also a fitness assessment. You will have to do a certain amount of each exercise (push-ups, sit-ups, etc...). Again, this varies from dojang to dojang.
At a certain level, your belt test will require sparring and/or board-breaking. Where this begins, again depends on your dojang. Many dojangs begin sparring at green belt.
There will probably be a "time in grade" requirement, i.e. you must hold each belt for a certain number of months before you can test for the next one. Many teachers suggest that earning your black belt can take anywhere from 2 years (too short, if you ask me) to 4 years. Don't get discouraged if you take longer than that, but do be suspicious if it takes less than 2 years. A black belt earned in that short of a time is probably not worth it. Also, bear in mind that the quoted time is if you train consistently, that is, at least two classes a week, if not three or even four. If you skip training because you're tired, you'll lose momentum and eventually get bored and lose interest.
I hate to give you the "it just depends" answer, but it really does just depend on where you train and who you train with. Your teacher is your best resource for this, though it is wise to field this question to the TKD community at large to see what is typical.