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Now, let us discuss two related algorithms for deciding which pages to evict. The clock algorithm is one of the most popular choices. It works by keeping frames in a circular structure. (Note that this circle may be very large: a 32-bit machine with 4k pages can have up to 220 1 million frames.) When a page fault occurs, it checks the reference bit of the next frame. If that bit is zero, it evicts that page and sets its bit to 1; if the reference bit is 1, the algorithm sets the bit to 0 and advances the pointer to next frame.
An implementation which is often used in real operating systems is a segmented queue. This type of algorithm divides all existing pages into two sets of pages. The most-active one-third of all pages use a clock algorithm. After that, pages that are evicted out of the clock are moved to a "uncommon" linked list, in which we use exact LRU. This way, we approximate LRU for the frequently-referenced pages (1/3 of the page frames - fast clock algorithm), and at the same time use exact LRU on the infrequently accessed pages (2/3 of all page frames). Since the pages in the uncommon list are not accessed very frequently, it is okay if their accesses are a little slower due to some pointer manipulation.
Q. What is the use of system programs? Answer: System programs are able to be thought of as bundles of useful system calls. They provide fundamental functionality to users so
Q. We have stressed the require for an operating system to make efficient use of the computing hardware. When is it suitable for the operating system to forsake this principle and
How does an operating system make multiprogramming possible by using single processor?
What is independent process? A process is independent it cannot influence or be affected by the other processes implementing in the system. Any process does not share data with
A page fault causes the following sequence to occur. 1. Trap (shut in) to the operating system. 2. Save the process registers and process state. 3. Verify that the interr
Parent process P creates three child processes, C1, C2, and C3. Each child process executes a memory and CPU intensive application of your choice. Your choice should be such that
Q. Why page sizes always powers of 2? Answer: Recall that paging is executed by breaking up an address into a page and offset number. It is most competent to break the address
How do we keep track of where the free pieces of memory are? One idea is to maintain a set of linked-lists of free space; each linked-list will store free chunks of some given size
what is difference between file descriptor and file pointer?
case study:interprocess communication
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