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Unformatted text preview: only the minimal facilities necessary for implementing
additional operating system services. The only services provided by the kernel in
this model are low-level device management, a limited amount of low-level
process management, and some memory management. All other operating system
services, such as file management, additional process and memory management
activities, and security are implemented as user-level server process. Each server
process has its lown address space and can be programmed separately.
Resident and Non-Resident Operating System Modules
With all the functionalities of an operating system implemented, it becomes a
large software. Obviously, all the functionalities of an operating system are not
needed all the time. As the main memory capacity of a system is limited, it is
customary to always keep in the system's memory only a very small part of the
operating system and to keep its remaining part on an on-line storage device such
as hard disk. Those modules of an operating system that are always kept in the
system's main memory are called resident modules and those that are kept onjlard
disk are called non-resident modules. The non-resident modules are loaded into
the memory on demand, that is, as and when they are needed for execution.
The system kernel should not be confused with the resident modules of the
operating system. The two are not necessarily the same. In fact, for most operating
systems they are different. The following two criteria normally determine whether
a particular operating system module should be resident:
1. Its frequency of use, and 2. Whether the system can operate at all without it.
For example, file directories can be maintained on disk and loaded into the
memory when required. Status information for inactive processes can similarly be
swapped out on disk. In fact, the resident part of an operating system is a subset of
OTHER RELATED CONCEPTS
Few other concepts related to operating systems are briefly described below. Real-time Operating Systems
For many applications, successful processing...
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- Spring '14