IGX - Cross-memory prefix

Privileged Operation: Requires the invoking program to be in supervisor state, APF-authorized, or have specific authorization to utilize cross-memory services.
Address Space Isolation: While enabling access, it maintains the integrity and isolation of individual address spaces, preventing unauthorized or accidental interference.
Performance Optimization: Facilitates efficient data transfer and program invocation between address spaces by avoiding the overhead of traditional task switching.
System-Level Control: Managed by the z/OS kernel and associated services, not directly manipulated by application-level code.
Integral to PC Services: Forms the foundation for Program Call (PC) services, which allow a program to branch to an entry point in another address space.
Security Mechanism: Includes checks to validate the authorization of the caller and the accessibility of the target resource, ensuring system integrity.

Enhanced Definition

In z/OS, the "cross -memory prefix" refers to the internal mechanisms and control blocks used by cross -memory services to manage and secure inter-address space communication. It enables a program in one address space to access resources or invoke code in another address space under strict authorization and control, without a full context switch.

- Subsystem Communication: Critical for major z/OS subsystems like CICS, DB2, and IMS to communicate with each other, system services, or specialized server address spaces.
- Data Sharing: Allows an authorized program in one address space to read or write data directly into the storage of another address space for high-performance data exchange.
- Program Call (PC) Invocation: Used when an application or system component needs to invoke a specific routine or service residing in a different address space.
- System Monitoring and Debugging: Tools that need to inspect or interact with the internal state of other address spaces often leverage cross-memory services.
- High-Performance Data Access: Enables specialized data servers to provide very fast access to shared data structures