There are four specialist areas of training in a full CompTIA A+ program; you’re considered an A+ achiever when you’ve passed the test for two of the four areas. For this reason, the majority of training establishments offer only two of the training courses. In fact you will need the training for all four areas as a lot of employment will require an awareness of each specialist area. You don’t have to take all four exams, although it would seem prudent that you at least have a working knowledge of every area.