Chapter 3 Operating-System Structures

1. System Calls

1.1. System calls provide the interface between a running program and the operating system.

1.2. Three general methods are used to pass parameters between a running program and the operating system.

1.2.1. -Pass the parameters in registers. -Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register. -Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system.

1.3. Types of System Calls

1.3.1. Process control File management Device management Information maintenance Communications Protection

2. Layer Approach

2.1. Advantage -Simplicity of construction and debugging Disadvantages -The careful definition and interaction of the layers -Less efficient

3. Microkernel

3.1. Small operating system core Contains only essential core operating systems functions Many services traditionally included in the operating system are now external subsystems o Device drivers o File systems o Virtual memory manager o Windowing system o Security services

4. Benefits of a Microkernel Organization

4.1. Reliability -Modular design -Small microkernel can be rigorously tested Portability -Changes needed to port the system to a new processor is changed in the microkernel - not in the other services

5. Operating System Design Goals

5.1. User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast. System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient.

6. Operating System Services User interface - Almost all operating systems have a user interface (UI) Program execution – The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error). I/O operations – Since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. File-system manipulation – Program capabilities to read and write files and directories, create and delete them, search them, list file Information, permission management. Communications – Processes may exchange information, on the same computer or between computers over a network Error detection – Ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.

7. Additional Operating System Functions Resource allocation – allocating resources to multiple users or multiple jobs running at the same time. Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics.

8. Operating System Design

8.1. Design and Implementation of OS not “solvable”, but some approaches have proven successful. Start by defining goals and specifications The design of the system will be affected by the choice of hardware and the type of system: batch, time shared, single user, multiuser, distributed, real time or general purpose.