Ah, a new approach to the perennial HNC question.
If you were to perform a search of this site using the keywords "unitary", "rack mount" and "modulular", you would find a wealth of information on the subject. Be advised that some of the information is not for the faint of heart!
Furthermore, here are a few unsolicited comments on your writing skills. It is customary in standard English to capitalize the first word of each sentence. Contractions apply an apostrophe to indicate the position of deleted letters. The correct spelling of a word synonymous with "advantages" is "benefits"