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CHAPTER 3 OPERATING SYSTEM ORGANIZATION
TOPICS:
i. Factors in Operating System design
ii. Basics OS function in computer
iii. Basic Implementation
consideration
Learning Objectives:OS design factors Essential and basic function for most
operating system available Implementation consideration for
developing OSLearning Outcomes Student know the factors that should be
consider for OS design and its necessity.
OS mechanisms
To enable process to create and destroy other process.
To request and release resources To use resources To coordinate its own operation with
the operations of related processes.
Factors in OS Design
Performance Protection & security Correctness Maintainability Commercial factors Standards and open systems
Application Integration
Interoperability
Portability
Strategies for open systemStrategies Explanation
Portability Application programs could be build so that they can be moved easily from one type of hardware to another
Application integrated All application programs could be built so that they present a common interface to users
Interoperability Facilities could be provide in a network environment to standardize access to remote facilities
Basic Functions
The OS provides mechanism for supporting an abstraction for computation for the process and for managing resources used by the community of processes.
4 categories OS functions: i. Device Management ii. Process and resource management iii. Memory Management iv. File Management
Device Management Refer to the way these generic
devices are handled.
Process and Resource Management
Processes basic unit computation ,and resources are the elements of the computing environment needed by a process to execute.
Most OS combine process and resource into a single module and define program execution
Memory Management Memory manager administers the allocation and use primary memory
resource. Every process request and uses memory according to the its program definition.
Modern primary memory managers provide virtual memory.
File are an abstract resource of storage devices.
Information stored in the main memory will be overwritten as soon as the memory is deallocated from a process. Information must be copied to a storage device.eg. Disk.,magenetic disk
File Management
Basic System Operating Organization
This section explains how the basic functions are combined to satisfy the requirements for an OS. Figure above shows the general organization for the basic OS modules (the lines between modules indicate interactions). This interaction is the basic rationale for a monolithic kernel OS design.
Basic Implementation Consideration
1. Processor Modes. - The mode bit it used to distinguish
between execution on behalf of an OS and execution on behalf of a user.
2. Kernels -. The kernel is designed as a
trusted software module that supports the correct operation of all over other software.
3 basic implementation mechanisms are used in every contemporary OS design:
Supervisor modeUser
mode
3. Method of requesting system device
This issue is concerned with the way user processes request services from the operating system: by calling a system function or message passing to a system.
i.Processor Mode
2 types of mode in processor: i. Supervisor mode: processor execute
every instruction in hardware ii. User Mode: execute only a subset of
the instructions. Supervisor mode also called supervisor,
priviledged, protected The mode bit is set by the user mode
trap instruction, also called supervisor call instruction
Supervisor and User Memory
ii.Kernels
The critical part of the system software that executes in supervisor mode.
All application program execute in user mode.
Kernels=Nucleus. Operated as trusted software, means
implement protection mechanisms that could not be changed actions of untrusted software executing in user mode.
iii. Requesting Services from the OS 2 techniques by which a program
executing in user mode can request the kernel’s services:
i. System call- a program that request a service from kernel and provide the interface between process and OS.
ii.Message passing
Procedure Call & Message Passing Operating Systems