If you are going to be working on a new PLC platform I would suggest your first course of action is to download and study the manuals.
For the CJ series you will need:-
W340 Instruction Set.
W393 Operation Manual
W394 Programming Manual
These are all available at the Omron Knowledge Center
http://www.omron247.com/doc/pdfcatal.nsfUse the Search and type the required W*** then download.
For answer to your specific question the memory layout is covered in SECTION 9 of W393.