Resource allocation allocating resources to multiple

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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. Protection – ensuring that all access to system resources is controlled.
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SUSHMA RAWAL 31 System Calls System calls provide the interface between a running program and the operating system. Generally available as assembly-language instructions. Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++) Three general methods are used to pass parameters between a running program and the operating system. Pass parameters in registers . Store the parameters in a table in memory, and the table address is passed as a parameter in a register. Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.
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SUSHMA RAWAL 32 Passing of Parameters As A Table
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SUSHMA RAWAL 33 Types of System Calls Process control File management Device management Information maintenance • Communications
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SUSHMA RAWAL 34 System Programs System programs provide a convenient environment for program development and execution. The can be divided into: File manipulation Status information File modification Programming language support Program loading and execution – Communications Application programs Most users’ view of the operation system is defined by system programs, not the actual system calls.
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SUSHMA RAWAL 35 UNIX System Structure UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts. – Systems programs – The kernel Consists of everything below the system-call interface and above the physical hardware Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.
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SUSHMA RAWAL 36 UNIX System Structure
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SUSHMA RAWAL 37 Layered Approach The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.
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SUSHMA RAWAL 38 An Operating System Layer
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SUSHMA RAWAL 39 Microkernel System Structure Moves as much from the kernel into “ user ” space. Communication takes place between user modules using message passing. Benefits: - easier to extend a microkernel - easier to port the operating system to new architectures - more reliable (less code is running in kernel mode) - more secure
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