sdram-dimm or edo dimm

my board no 1 tells me i can eighter use 3x128mb sdram or 3x 256 edo. i have only 3x168pin-dimm-slots.
my second board says: 3×128(8Mx8) or 3×256 16mx4 registered. is there a tools telling me if my existing modules are the right ones?
all must beunbuffered. is buffered inferior? is registered superior or does it depend on the machine?

the order does only matter for optimum ma time. how do i know them?