The archive is a special feature, and differs from the warehouse and inventory. The purpose of the archive it to be your personal “trophy rack” for awesome loot. Only Item mall items and high end rare item have a spot in the archive. Your archive is bound by account, not character. This means that any item you put in your archive can be taken out on any of your characters. You can see all the available items, so if you are the collector type try to fill it up!