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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.
what is file?explain the file access methods?
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What are the advantages of Contiguous allocation? The advantages are a. Supports direct access b. Supports sequential access c. Number of disk seeks is minimal.
how is it possible
What is a reference string? An algorithm is evaluated by running it on a particular string of memory references and computing the number of page faults. The string of memory re
Explain the Types of System Calls The major types of system calls are like this: a. Process Control: These types of system calls are employed to control the processes.
Logical File System Responsible for providing the before discussed interface to the user including: File access. Directory operations. Security and protection.
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