You can simply learn the real size of bios by looking at eeprom.
http://www.imsolidstate.com/wp-content/ ... 057376.jpgFor example
SST 25VF016B is 2mb. It depends to '16' section.
For MX
http://thumbs3.picclick.com/d/l400/pict ... -FLASH.jpg25L3206E is 4 mb. Depends 32 section.
10 : 128 kb, 20 : 256 kb, 40 : 512 kb, 80 : 1024 kb, 16 : 2048kb, 32 : 4096, 64 : 8192 kb, 128 : not yet in computers but 16384kb.