1st year Ph.D. student in Computer Science - want to switch fields I finished my Masters in Computer Science at a decently reputed university in the United States. I was (and still am) excited about doing research and I applied to the Ph.D. program at the same university. I was accepted and I started the program this Fall. 

Because of my experience in the department, I could start working in a lab from my first day in the Ph.D. program. I'm currently working on a topic that is closely related to my Master's thesis topic. But now I feel that I should explore other areas before committing on a Ph.D. topic. 

I've been working on Operating Systems for as long as I remember, but recently, I attended a couple of seminars on NLP and Bio-informatics that got me excited. I don't have any background in either topics. But this makes me think that I should take a semester to explore other areas of research in Computer Science. 

How should I go about this? 

Update - I told my advisor. He said I should devote 100% of my time on his project. I fired him.
First of all, it's better to make the exploration now than later. Having a good place to apply your CS knowledge can be very powerful, and now is a better transition time than you will ever receive in the future.

With that said, there are several bioinformatics courses online that you can try out; one popular one is Coursera. This allows you to spend a few hours per weekend exploring the topic from a well known professor, and can help you decide whether or not you are truly interested. From there, as @ff524 stated, it is best to ask your advisor for information on how to continue applying your skills to both your PhD and bioinformatics.