The document discusses IBM's memory management for Java applications. Memory management allocates discrete regions of unused memory to applications and reclaims memory when it is no longer being used. On IBM systems, memory management uses temporary dynamic memory like single-level storage and teraspace, as well as undefined memory mapped files for extended memory. Teraspace provides 1 terabyte address spaces for processes using separately allocated storage areas that can have addressability holes. Memory mapped files map storage areas to undefined files in the file system, redirecting memory access to file access.

1. IBM FILE SYSTEM

2. Memory management
The memory management component is responsible for the
efficient use of system memory by a java application.
Java programs run in a managed execution environment.
When a java program requires storage, the memory
management component allocates the application a discrete
region of unused memory. After the application no longer
refers to the storage, the memory management component
must recognize that the storage is unused and reclaim the
memory for subsequent reuse by the application or return it
to the operating system.

3. • Memory management on IBM i is based on
temporary, dynamic memory. Both single-level
storage (SLS) and teraspace are used. In
addition, for extended memory the so called
undefined memory mapped files (including
memory protection) are used. The memory
type is implemented in the same way as for
UNIX.

4. • In the single-level storage concept main
memory and auxiliary storage (for
example, disk storage) are considered as
a single large address space, whose
linearly addressable areas can grow to a
maximum size of 16 MB.

5. • A teraspace is temporary dynamic storage, that
provides an address space of 1 terabyte for
each process (that is, IBM i job). A teraspace
can consist of a number of separately allocated
and deallocated storage areas. Between these
areas, "addressability holes" can exist, that
is, storage areas that are not allocated. Although
teraspace is also based on single-level
storage, it is completely transparent to the
processes (IBM i jobs). This memory type is
used for the so called roll area.

6. • For memory mapped files, the storage
area with a given size is mapped to a
undefined file of a given size in the file
system. All commands that access the
memory space are redirected to file
access by the operating system. Memory
protection is achieved by explicit attach
and detach instructions to the extended
memory when activating and deactivating
a user context.

7. • IBM i means implementing proven
solutions on a platform you can trust. By
choosing the latest Power® platform, IBM i
applications get world class performance
plus dynamic infrastructure flexibility, with
the opportunity to lower monthly
operations costs.

8. • IBM i integrates a trusted combination of relational
database, security, Web services, networking and
storage management capabilities. It provides a broad
and highly stable database and middleware
foundation for efficiently deploying business
processing applications, with support for over 5,000
solutions from over 2,500 ISVs. i solutions are offered
through an extensive, highly skilled worldwide network
of IBM Business Partners that is backed by IBM’s
trusted services and support infrastructure.

9. • IBM develops, fully tests and preloads the core
middleware components of i together upfront, whereas
on other platforms, operating system, database and
middleware integration is done in the data center. The
preintegration and testing of i is a key factor in
enabling companies to deploy applications faster and
maintain them with fewer staff. Virtualization and
workload management are also built into i to enable
you to run multiple applications and components
together on the same system, driving up system
utilization and delivering a better return on IT
investments.