Operating Systems. Definition An operating system is a collection of programs that manage the...
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Transcript of Operating Systems. Definition An operating system is a collection of programs that manage the...
Operating Systems
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.
Types of Operating Systems
Simple device control embedded on a ROM chip
Complex Windows NT Unix, Etc.
Complex Operating Systems
Consist of multiple programs
The Kernel is the core of the operating systems.
Kernel
The kernel is responsible for:
Device control Memory management Scheduling Inter-process communication Processing of interrupts and exceptions.
Single vs. Multiple Processor
Single Processor can only run one instruction at a time.
It gives the appearance of multi-tasking with switching.
2 Types of Switching
Co-Operative Switching
Pre-Emptive Switching
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.
Problem with Co-Operative Switching
If first process “hangs up” and does not give up control the computer freezes. No other task can run.
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.
Pre-Emptive Switching is“Better” than Co-Operative Switching
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”.
Context Switching
The process of switching from one task to another is called “Context Switching”.
Scheduling
Scheduling is the process of deciding which task should run next.
Time Slice
The amount of time that a process runs before giving up control is called time slice or quantum period.
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.
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.
Multiprocessor vs. Multiprocessing
A multi-processor computer is a computer with more than one processor.
Categories of Multi-Processor Computers
Shared memory multi-processor
Distributed memory multi-processor
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.
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.
Related to Multi-Processors
Networked Systems
Distributed Systems
Networked Systems
Networked systems consist of multiple computers, networked together. Users are aware of the different computers that make up the system.
Distributed Systems
Distributed systems also consist of multiple computer but unlike the networked system the various computers are transparent to the user.
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.