There are several architectures proposed for building parallel DBMSs. Three main architectures include shared memory, shared disk, and shared nothing. As the name suggests, in the shared memory architecture, a global memory is shared. The shared-memory architecture is said to be closer to a conventional machine and easy to program, and the overhead is low. On the other hand, it leads to a bottleneck problem and might be a bit expensive to build.
The shared-disk architecture shares a global disk. It has similar benefits to the shared-memory architecture. In the shared-nothing architecture, each node has its own memory as well as storage, and nothing is shared between the nodes.