To reference the data in a data space, the program must be in access register (AR) mode. Assembler instructions (such as load, store, add, and move character) move data in and out of a data space and manipulate data within it. Assembler instructions can also perform arithmetic operations on the data.
When a program uses the DSPSERV macro to create a data space, the system returns a STOKEN that uniquely identifies the data space. (Data spaces do not have ASIDs.) The program then gains access to the data space: it uses the ALESERV macro to add an entry to an access list and obtain an access list entry token (ALET). The entry on the access list identifies the newly created data space and the ALET indexes the entry.
The process of giving the STOKEN to ALESERV, adding an entry to an access list, and receiving an ALET is called establishing addressability to the data space. The access list can be one of two types:
- A dispatchable unit access list (DU-AL) — the access list that is associated with a TCB or SRB
- A primary address space access list (PASN-AL) — the access list that is associated with an address space
