ClearPath OS 2200 Series Release 13.2 Software Planning and ...

Appendix D
BDI Allocation
A bank descriptor index (BDI) is the hardware name for a bank within the OS 2200
addressing architecture. It is a numerical index that points to a specific bank.
BDI allocation is a concern only at the application level of the OS 2200 address tree.
Banks at the application level are also known as application level banks, common banks,
or shared banks. These terms are all synonymous for code and data that is potentially
accessible from all runs, programs, and activities running within the system.
D.1. BDI Types
There are two types of BDIs: fixed and dynamic.
D.1.1. Fixed BDI
Fixed BDIs are permanently allocated to particular banks and products. This allocation is
globally defined and applies to all OS 2200 systems worldwide. In this way, programs
that need access to services provided by these common banks can be created with the
assurance that the targeted bank has the same index or name on any system.
D.1.2. Dynamic BDI
Dynamic BDIs are allocated to banks of object module subsystems (also known as
extended mode subsystems). These banks are loaded when a subsystem is activated, or
they are dynamically created during execution. Object module subsystems employ a
single fixed BDI, which points to a fixed gate bank. A gate bank contains one gate per
entry point into the subsystem. Gates are dynamically created and contain the acquired
BDIs for the other banks of the subsystem. The gate bank is built at the time the
subsystem is loaded, and it is updated when a bank is dynamically acquired. In this way,
all of the banks of the object module subsystem can be dynamically assigned BDIs,
rather than depend on fixed assignments. When the subsystem is deactivated, the BDIs
can be reused.
7831 0349–043 D–1