DDR2

DDR2 - memory interface with Double Data Rate access mode. This technology is the next level of the classical DDR memory interface.

DDR2 allow twice higher memory speed and use lower power because of lowering voltage from 2.5V (DDR) to 1.8V (DDR2). In other aspects - DDR2 technology is similar to DDR specification. Laptop DDR2 come with 200 pins. The maximum bandwidth is 1066 Million data transfers per second, it is marked as PC2-8500(8600) and use 533 MHz frequency. The minimum bandwidth is marked as PC2-3200 and use 200 MHz with 400 Million data transfers per second.
Laptop DDR2 memory is labeled with additional S in abbreviation.

DDR2 has no capability with DDR memory. Therefore laptops that used DDR memory cannot use DDR2 memory and in other way - DDR2 mother board cannot use DDR memory.

But you can use different DDR2 memory sticks in the same Laptop computer. For example if PC2-3200 and PC2-8500 is installed in one Laptop computer, then memory slot with higher performance will be automatically switched to lower performance, that is equal to PC2-3200.