Reg Data fields in DSO

Hello SAP Guru's!!!!

I have some doubt on maximum number of data fields in DSO. I gone through so many threads on SCN, but could not clarify my doubt.

The max no of key fields in DSO is -- 16

Max no of data fields in DSO is --749.

But i read in some of the scn documents  a table can have maximum 256 columns .

DSO is also like a two dimensional table which can also have the same properties of a two dimensional table.

if the above statement of mine is correct.. the number of columns in a DSO is 256 columns = 16(primary key)+240 (data fields--non key fields)

but how come 749 data fields (max) will be there ? if it is so ... the max no of  fields will be  749+16 = 765.

I need some clarification on this ....

Awaiting for your responses!!!!

regards,

vamshi