A decoding structure for a memory device with a control code is used in a memory including a matrix of memory cells grouped into pages to each of which a block of control information is associated, and a plurality of reading elements for reading a plurality of pages in parallel. The selection-information acquiring unit acquires selection information including information representing an additional apparatus which is selectable in accordance with a combination of one or more types of additional apparatuses connectable to the image forming apparatus. In one form of operation the compressor can close down the vanes to a relatively low flow capacity position and the compressor can be operated at a higher speed, whereupon the vanes can be repositioned and the gas turbine engine operated at a different condition. Access is permitted or denied according to access policies, which define access in terms of the user groups and information sets.