[LinuxBIOS] SPD Logical and Physical Banks

Hello,
Can someone please explain to me the difference between Logical and  
Physical Banks on SDRAM? I am looking for a quick and dirty way to  
determine if the SDRAM module is single sided or double sided through  
SPD. Would I use the Logical (SPD Byte 17) or Physical (SPD Byte 5)  
Bank for that?

Thanks - Joe