Aditya Abeysinghe OS

Multiprocessing is the use of two or more processors to share system resources. Multiprocessing enhances a system's performance by increasing reliability and enhancing faster processing. For example, consider a simple set of jobs as follows: When the execution is done using a single processor, only one job could be executed at a time. The other jobs have to wait until the job which is being currently executed runs to completion or preempted. This seriously degrades system performance since the waiting queues increase over time and the throughput is decreased. Some jobs may even lead to starvation (more about these concepts in the blog post on deadlocks and starvation). However, when the execution is done using multiple processors, many jobs can execute at the same time. This does not eliminate waiting queues or aging, but generally reduce them. Moreover the throughput is increased while decreasing the turnaround time. However, with every new concept comes a n

What is the Windows NT logon process? Windows NT process is the process by which the operating systems belonging to the Windows NT family start up. The logon process for operating systems introduced by Microsoft since Windows Vista uses a slightly different architecture (methodical steps), but many steps in the windows NT process have been repeated There are many steps involved with the Windows NT logon process but this blog post summarizes the most important steps and definitions. The basic architecture of this process can be summarized as follows: A simplified Windows NT logon process Now let us understand what each section of the above flow diagram does in the Windows NT logon process. Main sections of the logon process- Security reference monitor- The security reference monitor is used to ensure which subjects have authorization to which objects. Thus, it uses the access control policy used in the operating system for its basic functioning. A security refere

What are they? First-fit and Best-fit are memory allocation schemes that were typically used in dynamic and fixed partition memory allocation schemes to allocate memory. To simplify what they are, consider the following list of jobs and the available resources. The above figure shows a list of jobs and the resources to which these jobs could be allocated.  Here to allocate the jobs, we use either the first-fit memory allocation scheme or the best-fit memory allocation scheme. The first-fit memory allocation scheme allocates on the basis of the first partition fitting the requirements.  The best-fit memory allocation scheme allocates on the basis of the best partition (one with the least memory wastage) fitting the requirements. Let us allocate the jobs first on the basis of first-fit memory allocation and then on the basis of best-fit memory allocation to understand how jobs are allocated and the pros and cons of the two schemes. Allocating using First-fit memor