Difference between SD RAM and DDR RAM

I just want the know what are the difference between DDR and SD RAM. The only thing that I know is DDR is running at 226,333 and 400mhz compared to SD RAM which is running at 133mhz.

What are the benefits of DDR RAM ? How much performance increase if I use DDR RAM ? Is it 100 % because it is running at higher speed ?

Is it worth it if I use DDR RAM for my PC.
I use my PC for mainly gaming, surfing, music, typing work and CD-burning.

Theoretically 266Mhz memory is 100% faster than 133Mhz memory is. In real life, the performance gain is much lower. If the change is worth it totally depends on the software you use.

For your purpose, the only thing that’ll really run faster are games. Not all games by the way, only those ones that use the higher memory bandwith. A good example is Quake 3, using faster memory on that one will give it a performance boost.

Another important factor is your CPU. Any AMD processor will surely benefit from the higher memory bandwith, a P4 will suffer from this bandwith (P4->Rambus is ideal). A P3 will run about as fast with DDR as it will do with SDR.

Does that means using Athlon XP with SD RAM is like Michael Schumacher driving a Minardi or David Beckham playing with a Third Division Club ?

Looks like DDR is good for games.