5. What is the cause of thrashing? How does the system detect thrashing? Once it

Question

5. What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

1.. Calculate the total head movements for the following queues using C-LOOK (head starts at 53)

46, 73, 11, 20, 151, 115, 130, 49

2.. In what ways is using a nameserver better than using static host tables? What problems or complications are associated with name servers? What methods could you use to decrease the amount of traffic nameservers generate to satisfy translation requests?

3. What is the purpose of system calls?

Explanation / Answer

Thrashing:

Performance of systems has not always met expectations because it depends on many factors, paged memory inefficiency causes some lagging in performance. Thrashing is nothing but caused by under allocation of the minimum number of pages than required by a process. Causes to continuously page fault. The system can detect thrashing by evaluating CPU utilization by comparing multiprogramming. It result in severe performance problems.

If the level of assigning multi programming greater than the CPU capacity.As the degree of multiprogramming increases, CPU utilization also increases.If the degree of multiprogramming is increased, thrashing increases and causes systems to work slowly.

To prevent or limit thrashing, several techniques are used.
The Working of Set Model: It shows how many frames a process using and then defines the locality model. Locality Model states that as a process executes, it then moves from locality to locality. A locality is nothing but a set of pages that are actively used together.

2)Name server is nothing but a category of a server on the internet specialized in handling queries about the location of a particular domain name’s various services.Name servers are sub parts of the Domain Name System (DNS). They allows requests based on domains instead of IP addresses. Name servers define your domain’s current DNS provider. Most domain name registrars contains DNS services.

Suppose when a user enters a URL www.youtube.com, the request not directly sent to the youtube servers. First the request goes to a DNS server, contains a look-up table to determine and divide as several pieces of information ,then forwards this request to the proper servers.

Benefits:

Name servers allow Internet users to use Internet resources without having to remember port numbers and IP addresses. This allows users to memorize simple URL addresses but not as difficult IP addresses. This also allows users to made be freely available even they don’t know their IP address.

Disadvantages:

Requests that are generated through DNS are vulnerable to fake requests from a spoofed IP address, the spoofed IP address can get harmed by the number of DNS results it receives and be unable to serve regular Internet traffic. Based on this draw back, third party Network administrators who detect these requests may block IP addresses.

3)System calls:

The main purpose of system callls is,they provides an interface to the operating system services.System calls allow users to request services of the operating system. Developers often do not have direct access to the system calls, but can access them through an API.For example, if we want to perform the activity of read and write in a file ,then system requires input or output from storage,such system call operations are able to provide users as system calls or APIs - read(), write(). There are several types of system calls like process management,device management, file management, information management and communication.

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