Address Space

Enhanced Definition

A virtual storage area assigned to a program or task, providing isolation between different executing programs. Each address space has its own private virtual storage and can contain multiple tasks, enabling multiprogramming on z/OS. An address space in z/OS is a range of virtual storage addresses that is uniquely available to a single job, started task, or TSO user. It provides an isolated, private execution environment where programs can access instructions and data using virtual addresses, which are then translated to real storage by the operating system and hardware.

Key Characteristics

- Up to 2GB virtual storage in 31-bit addressing
- Up to 16EB (exabytes) in 64-bit addressing
- Private and common storage areas
- Protected from other address spaces
- Managed by z/OS memory management
Address Space Structure:
- Private Area: Unique to each address space, contains user programs and data
- Common Area: Shared across all address spaces, contains system code and data
- System Area: Contains z/OS nucleus and control blocks
- Extended Private: Storage above 16MB line (EPVT)
- 64-bit Regions: Storage above 2GB bar
Address Space Types:
- User Address Spaces: Run application programs (batch jobs, TSO users)
- System Address Spaces: Run z/OS components (JES2, VTAM, RACF)
- Subsystem Address Spaces: Run subsystems (CICS, DB2, IMS)
- Started Tasks: System services and middleware
Memory Management:
- Virtual-to-real address translation via DAT
- Paging between real and auxiliary storage
- Storage protection keys prevent unauthorized access
- Swapping for memory optimization

Use Cases

- Isolating applications for security and stability
- Running multiple batch jobs concurrently
- Supporting online transaction processing systems
- Providing dedicated environments for subsystems
- Managing memory resources efficiently