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Though it may be difficult, 4 papers isn't impossible for computational biology, depending on the content.

In computational biology there is really a wide variety of paper types - experimental, computational modelling/analysis of data, completely theoretical. Some papers are even focused on just describing tools. The requirement of IF>2 is very low for this field (I don't even recall seeing something that low), so I suspect the idea is to go - in the worst case - for quantity rather than quality (e.g. salami slicing or least publishable unit). Personally I am not a fan of this way of publishing but there are many who adhere to it, and I can understand why. I am guessing that the supervisor thinks this way is better for you. This way you have a good chance to get several publications, but if you put everything together into one paper in order to get it into a prestigious journal, there is a chance that paper will not be accepted or will only be accepted into a bad journal, and that could mean trouble.

So, for example (though a bit extreme in my view), If you have an idea for a new bioinformatic tool, you could write one paper just on the theoretical part (maybe with some simulations on synthetic data), a second paper on applying it to biological data and correlating with other biological datasets, and a third short paper on the tool itself (maybe you set up some website/server etc).

Of course the best thing is to get 4 landmark papers in prestigious journals, but I wouldn't count on that...