Novell NETWARE 6-DOCUMENTATION Manual page 2924

Protected Address Spaces
Protected Address Spaces and Logical Memory Addressing
12
Server Memory Administration Guide
Portions of the logical address space are set aside for protected address spaces
(sometimes called user address spaces or ring 3). This protected address space
is a portion of the logical address space that has carefully controlled
interaction with the server operating system. All protected address spaces use
virtual memory. For general information about virtual memory, see
Memory" on page 14.
A key benefit is that you can use protected address spaces to take advantage
of virtual memory or to run untried or troublesome applications. Because any
modules loaded into a protected address space can't corrupt the operating
system or cause server abends, the protected address space provides a safe
place to run applications.
The operating system address space (ring 0) is sometimes called the OS
address space or the kernel address space. The memory protection marshalling
layer, in conjunction with the memory protection subsystem, prevents
modules in a protected address space from having direct access to anything
outside the address space. In particular, the memory protection marshalling
layer serves as the interface between the protected address spaces and the
server operating system. These layers prevent NLM programs in protected
spaces from making calls or passing parameters to the operating system that
would corrupt or fault the core operating system.
You can load modules into a protected address space, unload modules from a
space, delete a space, or kill a space. See
on page 34 and "Loading Protected Address Spaces" on page
Each protected address space has its own set of page translations to provide
logical memory addressing. The memory management subsystem ensures that
the page translations of each protected address space refers to a different set
of physical memory addresses.
Only one set of translations is visible in the memory management subsystem
at a time. When there is more than one protected address space, the memory
management subsystem loads one set of page translations for a specified time
and then replaces it with another.
"Using Protected Address Spaces"
"Virtual
35.