operating systems. definition an operating system is a collection of programs that manage the...
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Operating Systems
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Definition
An operating system is a collection of programs that manage the resources of the system, and provides a interface between the user, the hardware, and the applications.
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Types of Operating Systems
Simple device control embedded on a ROM chip
Complex Windows NT Unix, Etc.
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Complex Operating Systems
Consist of multiple programs
The Kernel is the core of the operating systems.
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Kernel
The kernel is responsible for:
Device control Memory management Scheduling Inter-process communication Processing of interrupts and exceptions.
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Single vs. Multiple Processor
Single Processor can only run one instruction at a time.
It gives the appearance of multi-tasking with switching.
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2 Types of Switching
Co-Operative Switching
Pre-Emptive Switching
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Co-Operative Switching
In co-operative switching the task which is currently running must voluntarily give up the processor for the next process to run.
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Problem with Co-Operative Switching
If first process “hangs up” and does not give up control the computer freezes. No other task can run.
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Pre-Emptive Switching
In pre-emptive switching the task that is currently running is forced to give up control after a certain period of time. If a task “hangs” it does not stop subsequent task from running.
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Pre-Emptive Switching is“Better” than Co-Operative Switching
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16-Bit vs. 32-bit
32-bit programs use pre-emptive switching.
16-bit program use co-operative switching and are more susceptible to “freezing”.
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Context Switching
The process of switching from one task to another is called “Context Switching”.
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Scheduling
Scheduling is the process of deciding which task should run next.
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Time Slice
The amount of time that a process runs before giving up control is called time slice or quantum period.
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Co-Operative Processing
In co-operative processing the processes are generally arranged such that as the top process is completed each task moves up one place.
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Pre-Emptive Scheduling Pre-emptive scheduling uses a real-
time clock, which generates interrupts at regular intervals. Each time an interrupt occurs the processor is switched to another task.
Generally tasked are assigned a priority in pre-emptive scheduling.
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Multiprocessor vs. Multiprocessing
A multi-processor computer is a computer with more than one processor.
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Categories of Multi-Processor Computers
Shared memory multi-processor
Distributed memory multi-processor
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Shared Memory Multi-processor
Shared memory multi-processors have multiply CPUs, and they all share the same memory.
Communication between the processors is easy to implement, but care must be taken to synchronize memory access.
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Distributed Memory Multi-Processors Also has multiple CPUs, but each
CPU has its own memory. In distributed memory multi-
processor memory synchronization is not a problem,
but communication between the processors is often slow and complicated.
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Related to Multi-Processors
Networked Systems
Distributed Systems
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Networked Systems
Networked systems consist of multiple computers, networked together. Users are aware of the different computers that make up the system.
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Distributed Systems
Distributed systems also consist of multiple computer but unlike the networked system the various computers are transparent to the user.
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Operating System A computer is a set of resources for
the movement, storage, and processing of data.
The operating system is responsible for managing these resources scheduling the other programs and providing the user interface.