Final answer:
The access to central storage in a System z architecture is synchronous, which allows for tightly timed exchanges between the CPU and memory for high-speed processing.
Step-by-step explanation:
The question you've asked pertains to a System z architecture, which is a family of mainframe computers designed by IBM. These systems categorize their physical storage into two main types: central storage and auxiliary storage. When speaking about the access to central storage on these mainframes, it is important to recognize that the data access is designed to be highly efficient and tightly integrated with the CPU operations. Therefore, the correct answer to your question is: Access to central storage is C. synchronous.
In computing, synchronous access is when the CPU and memory exchanges are tightly timed and coordinated, which is essential for high-speed processing in mainframe environments. As such, System z architectures are built to handle large volumes of transactions and operations that require quick and synchronized access to central storage. This contrasts with asynchronous access, where data exchanges between the CPU and storage can occur at irregular intervals, and duplexed, which refers to a fault-tolerant design involving two components.