Problems left unsolved by the related art that are solved by the present invention should be discussed. This is the first place in the disclosure that a foundation for subsequent arguments that the invention meets the three criteria for patentability (utility, novelty, and unobviousness) can be presented. This is accomplished by pointing out the limitations of the related art - thus setting the stage for a delineation of the advantages of the present invention in the (next) Summary of the Invention section.
Here you have to walk the fine line between pointing out the limitations or problems involved in the related art (that are solved by your invention) without making derogatory remarks concerning the inventions of others. According to the rules, "mere comparisons" with the related art are OK.
Take care not to call anything "prior art" because the definition of that term is very complex and the mere fact that you call a reference "prior art" in a patent application means that the patent office can assume that what it discloses was invented before you made your invention. You can call technology in your description of the state of the art "related art" or "background art" but never specifically state that anything existed before you made your invention - because you could be permanently wrong. (Weird rules, huh?)
When a patent application is filed, this information will become a part of the Background of the Invention section.
Law - Limitations of the Background Art