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.