Sdram has one notch. Depending upon the model of Sdram the number of pins it has can vary but a standard Sdram has 184 pins.
1 notch
one notch
DDR SDRAM has one notch and uses 184 pins.
168-pin SDRAM DIMM
Peripheral Wrong dumbo, it is a SERIAL BUS
SDRAM has 168 pins and two notches on the module.
No. SDRAM has two notches and DDR SDRAM has only one so besides all the electrical incompatibilities it won't physically fit.
The positions of two notches on a SDRAM DIMM identify the type of DIMM and the voltage requirement and also prevent the wrong type from being installed on a motherboard.
DIMM. Two types of DIMMs: a 168-pin SDRAM module (top) and a 184-pin DDR SDRAM module (bottom). Note that the SDRAM module has two notches (rectangular cuts or incisions) on the bottom edge, while the DDR1 SDRAM module has only one.
DDR SDRAM uses 184 pins.
2.66" 189-pin SO-DIMM contains DDR SDRAM 2.66" 189-pin SO-DIMM contains DDR2 SDRAM 2.66" 145-pin SO-DIMM contains SDRAM 2.35" 40-pin SO-DIMMs (outdated) 130-pin SO-RIMM (conatains Rambus memory and has two notches).
While I'm sure a destructive lunatic could force a DDR module into an older slot, they are not designed to be physically compatible. DDR modules have only a single notch, while SDR modules and slots are keyed with two notches and ridges.