According to this reference data sheet:

http://www.datasheetcatalog.com/datasheets_pdf/H/Y/B/3/HYB3164400AJ-60.shtml

Each chip is 64 Megabits, or 8MB. And there are 8 chips total, so 8*8=64MB

Well then it is a 64MB module! But why will only 16MB be detected?