If the motherboard supports both DDR and SDR RAM, it is almost always a better idea to go with DDR RAM
Yes they are definitely different as DDR stands for Double Data Ram & SDR stands for Single Data Ram and further explanation can be found here http://en.wikipedia.org/wiki/DDR_SDRAM
yes
No.
DDR, DDR2, SDR, DDR3, DDR4. SO-dimm are for laptops
No.
No.
512 SDR. DDR2 is better, but more the memory better it is for your PC, irrespective of the memory technology. You have a point there but considering the current trends, i will prefer the DDR because sdram is being replaced with ddr. Especially if you planning to buy a new mother board, most MoBo's nowadays are of ddr. But speed and capability is better than having plenty of ram. It is with the speed of access not only the space. Besides, it's better to consider efficiency, right?
No. SDR SDRAM and DDR SDRAM modules are not interchangeable.
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.
yes, you can. Make sure they're all the right speed and type of RAM though. If you're putting older sticks of SD RAM in a newer computer that uses DDR RAM, you'll either get errors or just lacking performance.
Motherboards of that era would have had a either a combination of the older SDR SDRAM (PC100 or PC133 RAM) and DDR SDRAM, or just DDR SDRAM.For best performance, you would want to use the DDR slots.
PC133 Ram and PC333 ram are generally incompatible. PC133 RAM is SDR Ram where as PC333 is DDR RAM. Some motherboards support using either SDR or DDR but this is not usual. PC133 will not fit in the same slot as PC333.