Processing modes

The processing modes follow. Code always runs in one or more of these modes. For example, code running in task or service request block (SRB) mode can also be either locally locked or physically disabled.

Task mode is the most common processing mode. All programs given control by ATTACH, ATTACHX, LINK, LINKX, XCTL, and XCTLX macros run in task mode.
SRB mode is code that runs from one of the service request block (SRB) queues.
Physically disabled mode is reserved for high-priority system code that manipulates critical system queues and data areas. This mode is usually combined with supervisor state and key 0 in the PSW. The combination ensures that the routine can complete its function before losing control. The mode is restricted to just a few modules in the system, for example, interrupt handlers, the dispatcher, and programs that are holding a global spin lock.
Locked mode is for code that runs in the system while holding a lock.
Cross memory mode. Cross memory mode is defined by:
- Primary address space: Address space identifier (ASID) in control register 3
- Secondary address space: ASID in control register 4
- Home address space: Address of the address space control block (ASCB) in the PSAAOLD field
- PSW S-bit (bit 16 of the PSW): Indicator of current addressability:
  - S-bit=0 - To the primary address space
  - S-bit=1 - To the secondary address space
  When primary addressability and secondary addressability are to the home address space and the S-bit=0, the work is not in cross memory mode.
Access register (AR) mode, where a program can use the full set of assembler instructions (except MVCP and MVCS) to manipulate data in another address space or in a data space. Unlike cross memory, access registers allow full access to data in many address spaces or data spaces.