CompTIA A+® Certification All-In-One For Dummies®, 2nd Edition

3.6. Single Sided Versus Double Sided

Memory modules are either single-sided or double-sided memory modules, but this characteristic does not mean that the memory chips exist on only one side of the memory card or both sides of the memory card (which is what most people think).

For single-sided memory, all the memory on the memory module is accessed at once by the system and is treated as a single "bank" of memory. It is important to note that the memory chips on a single-sided memory module may exist on both sides of the memory board.

For double-sided memory, the memory module (or memory board) is divided into two discrete chunks of memory (banks). The system can access only one bank at a time. Original double-sided memory modules were created by taking two single-sided memory modules and connecting them.