What is multiprogramming?Multiprogramming is a rudimentary form of parallel processing in which several programs run at the same time on a uniprocessor system. However, because there is only one processor, there is no true simultaneous execution of different programs. Instead, the operating system (OS) executes part of one program, then part of another, and so on. In this sense, multiprogramming can be thought of as pseudo-parallelism. To the user, it appears that multiple programs are executing at the same time, but that is not what is happening. Show
Prior to the introduction of multiprogramming, single processor computers could run only one program at a time. Once the program was launched, it ran to completion, unless it was interrupted or the application ceded control. Only after the first program finished running could the processor execute the next program in the queue. This meant that the CPU sat idle during I/O operations, even if other programs were waiting, resulting in application delays and underutilized processor resources. Multiprogramming addresses this issue by allowing multiple programs to load into memory and run each one in rotation as CPU resources become available. For example, when Program A starts, the operating system assigns CPU resources to that program until the program launches into its I/O operations. Then, the OS assigns CPU resources to Program B, which is already loaded into memory. If Program B launches into I/O operations and Program A is still running its I/O operations, the OS will assign CPU resources to Program C; otherwise, it will assign them back to Program A. The operating system is responsible for ensuring that CPU resources are properly allocated and reallocated to each program as resources become available, working around the various program's I/O operations. To achieve this, the OS uses a technique called context switching, which ensures that a program's state is preserved in memory and can be readily accessed as the OS switches between programs and CPU assignments. The purpose of multiprogramming is to maximize CPU time.Types of multiprogrammingMultiprogramming is implemented in one of two ways: cooperative multiprogramming or preemptive multiprogramming. Cooperative multiprogramming is the older of the two models and is seldom used today. With cooperative multiprogramming, context switching is initiated by the programs themselves rather than the OS. Processor resources are reassigned only when a program releases control of those resources. The operating system has no choice but to execute a program with the expectation, but not the certainty, that the program will eventually return control to the OS. The problem with this approach is that a program can monopolize CPU resources for an inordinate amount of time, keeping other programs waiting. Even worse, a buggy or malicious program might launch an infinite loop and never give up control of the CPU, resulting in a locked system or system crash. Not only does this disrupt user and application workflows, but it can be difficult to debug because it might not be obvious which of several programs is at fault. With preemptive multiprogramming, the OS has complete control over context switching. It allocates CPU resources based on queued programs and their I/O operations, while limiting the time each program can run. So, if there is a problem with one of the programs, it cannot interfere with operations indefinitely. Today, most computers use preemptive multiprogramming.
See also: multiprocessing This was last updated in May 2022 Continue Reading About multiprogramming
1. Multi programming –In a modern computing system, there are usually several concurrent application processes which want to execute. Now it is the responsibility of the Operating System to manage all the processes effectively and efficiently. One of the most important aspects of an Operating System is to multi program. In a computer system, there are multiple processes waiting to be executed, i.e. they are waiting when the CPU will be allocated to them and they begin their execution. These processes are also known as jobs. Now the main memory is too small to accommodate all of these processes or jobs into it. Thus, these processes are initially kept in an area called job pool. This job pool consists of all those processes awaiting allocation of main memory and CPU. CPU selects one job out of all these waiting jobs, brings it from the job pool to main memory and starts executing it. The processor executes one job until it is interrupted by some external factor or it goes for an I/O task. Non-multi programmed system’s working –
The main idea of multi programming is to maximize the CPU time. Multi programmed system’s working –
In the image below, program A runs for some time and then goes to waiting state. In the mean time program B begins its execution. So the CPU does not waste its resources and gives program B an opportunity to run. 2. Multiprocessing –In a uni-processor system, only one process executes at a time. Multiprocessing is the use of two or more CPUs (processors) within a single Computer system. The term also refers to the ability of a system to support more than one processor within a single computer system. Now since there are multiple processors available, multiple processes can be executed at a time. These multi processors share the computer bus, sometimes the clock, memory and peripheral devices also. Multi processing system’s working –
Why use multi processing –
Multiprocessing refers to the hardware (i.e., the CPU units) rather than the software (i.e., running processes). If the underlying hardware provides more than one processor then that is multiprocessing. It is the ability of the system to leverage multiple processors’ computing power. Difference between Multi programming and Multi processing –
3. Multitasking –As the name itself suggests, multi tasking refers to execution of multiple tasks (say processes, programs, threads etc.) at a time. In the modern operating systems, we are able to play MP3 music, edit documents in Microsoft Word, surf the Google Chrome all simultaneously, this is accomplished by means of multi tasking. Multitasking is a logical extension of multi programming. The major way in which multitasking differs from multi programming is that multi programming works solely on the concept of context switching whereas multitasking is based on time sharing alongside the concept of context switching. Multi tasking system’s working –
In a more general sense, multitasking refers to having multiple programs, processes, tasks, threads running at the same time. This term is used in modern operating systems when multiple tasks share a common processing resource (e.g., CPU and Memory).
4. Multi threading –A thread is a basic unit of CPU utilization. Multi threading is an execution model that allows a single process to have multiple code segments (i.e., threads) running concurrently within the “context” of that process. e.g. VLC media player, where one thread is used for opening the VLC media player, one thread for playing a particular song and another thread for adding new songs to the playlist. Multi threading is the ability of a process to manage its use by more than one user at a time and to manage multiple requests by the same user without having to have multiple copies of the program. Multi threading system’s working – Example 1 –
Example 2 –
The image below completely describes the VLC player example: Advantages of Multi threading –
What is responsible for multitasking on computer?Multitasking is used to keep all of a computer's resources at work as much of the time as possible. It is controlled by the operating system, which loads programs into the computer for processing and oversees their execution until they are finished.
What are the types of multitasking?There are two types of multitasking:. Preemptive multitasking. In preemptive multitasking, the operating system decides how to allocate CPU time slices to each program. ... . Cooperative multitasking. In cooperative multitasking, each program controls how much CPU time it needs.. In which multitasking model does the operating system manage the coordination of multiple tasks?Preemptive multitasking
It also allows the system to deal rapidly with important external events like incoming data, which might require the immediate attention of one or another process. Operating systems were developed to take advantage of these hardware capabilities and run multiple processes preemptively.
What are the two types of multitasking operating system?There are mainly two types of multitasking. These are as follows: Preemptive Multitasking. Cooperative Multitasking.
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