Finally we have the differences at the physical level. You buy memory chips already soldered on a printed circuit board called “memory module”. Memory modules for each DDR generation are physically different and you won’t be able to install a DDR2 module on a DDR3 socket, for example. Unless your motherboard supports both DDR2 and DDR3 sockets (only a few do) you cannot upgrade from DDR2 to DDR3 without replacing the motherboard and eventually the CPU (if in your system the memory controller is embedded in the CPU, like it happens with all processors from AMD and Core i7 from Intel). The same thing is valid with DDR and DDR2: unless for a few are rare exceptions, you cannot replace DDR memories with DDR2. DDR2 and DDR3 modules have the same number of pins, however the key notch is placed on a different position.

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Figure 7: Difference in edge contacts between DDR and DDR2.

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Figure 8: Difference in edge contacts between DDR2 and DDR3.

All DDR2 and DDR3 chips use BGA (Ball Grid Array) packaging, while DDR chips almost always use TSOP (Thin Small-Outline Package) packaging. There are a few DDR chips with BGA packaging on the market (like the ones from Kingmax), but they are not so common. On Figure 9 you can see how a TSOP chip on a DDR module looks like while on Figure 10 you can see how a BGA chip on a DDR2 looks like.

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Figure 9: DDR chips almost always use TSOP packaging.

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Figure 10: DDR2 and DDR3 chips use BGA packaging.