According to 2009 IBC Chapter 6, Type I thru Type IV construction is divided by the use of non-combustible vs. combustible materials.  The addition of A or B defines if the construction is protected or unprotected which is the fire resistance protection applied to structural members and bearing walls; i.e. firerated gypsum board, spray-on fire protection, etc. etc. (not the same as sprinkled or non-sprinkled).  Now the question:  If type "B" is considered to be "Unprotected", why does Table 601 require fire resistance ratings (applied protections) to "B" categories?