What defines a one-tier architecture in database systems?

A one-tier architecture in database systems is defined by having all components, including the database and the processing logic, located on a single CPU. This setup means that the client and server functionalities are combined, allowing for direct interaction with the database without the need for intermediary layers or servers. Such an architecture is typically simpler and easier to implement in smaller applications or for development environments where performance needs can be easily met by a single machine.

In this architecture, the client applications can directly access the database, enabling straightforward communication. This contrasts with multi-tier architectures where different components might be distributed across multiple servers, thereby increasing complexity and potentially improving scalability and performance but requiring more sophisticated management.

The other options describe characteristics associated with different architectures or environments. For example, placing multiple components on different servers indicates a multi-tier architecture, while complex tiered access management is tied to systems where multiple layers and components must interact securely. Similarly, cloud environments can utilize any architecture tier but aren't specific to the definition of one-tier systems.