Columbia Computer Science Hw-1

Topics: Internet, OSI model, Internet Protocol Suite Pages: 8 (2462 words) Published: April 5, 2012
What is the difference between the process that is ready and the process that is waiting?

A process is ready when it is in a state to move on to the next level or it can continue its process A process that is waiting is when progress is currently delayed until some external events occur that needs completion for the process to move to the next level

What is the difference between main memory and virtual memory?

Main memory is also known as the Random Access Memory. Main memory is the immediate storage within the computer and to access any source of Information from the computer the information first has to be copied onto the main memory for the computer to read. In contrast virtual memory is when memory manager shuffles the data back and forth between the main memory and mass storage, to create imaginary memory space in the main memory so that large files can be viewed.

If a typist types 60 words per minute (where a word is considered 5 Characters) how much time would pass between typing each character? If a multiprogramming operating system allocated time slices in 20 Millisecond units we and we ignore the time required for process switches, how many time -slices could be allocated between characters being typed?

60 words per minute = 1 word per second.
5 characters in each word, which is which is 200 second per character At 20 millisecond per time slice, which is 200/20 = 10 time slices per character

Since each area in a computer monitor screen can be used by only one process at a time (otherwise the image on the screen would be unreadable) these areas are non-sharable resources that are allocated by the window manager. Which of the three conditions necessary for deadlock does the window manager remove in order to avoid deadlock?

The condition is mutual exclusion and the condition that can be used to remove the deadlock is by converting non-sharable resources into sharable ones. The operating system could make the non-sharable resource appear sharable by spooling, which would hold data for output for at a later but convenient time. The other condition could be through deadlock detection and correction scheme, where the window manager can manually detect the deadlock and release space for the process to move smoothly, since the computer monitor screen can be used by only one process at a time. A process that is waiting for time slice is said to suffer starvation if it is never given a time slice

a) The pavement in the middle of an intersection can be considered as a non-sharable resource for which car approaching the intersection compete. A traffic light rather than an operating system is used to control the allocation of the resource. If the light is able to sense the amount of the traffic arriving from each direction and is programmed to give the green light to the heavier traffic, the lighter traffic must suffer from starvation. How is starvation avoided?

To avoid starvation of the lighter traffic every time the lighter traffic does not get a time slice its priority increases. The time slice can then use the interrupt signal that can be send to the dispatcher, In this case the traffic light so that the lighter traffic gets an equally high priority. Alternating the priority between the high traffic and low traffic when it reaches high priority will keep the traffic moving both ways.

b) In what sense can a process starve if the dispatcher always assigns time slice according to a priority system in which the priority of each system remains fixed? How would you guess do many operating system avoid this problem?

If the priority of each system remains fixed than the lighter traffic will never be able to move until the heavier traffic has cleared. Therefore if the priority is fixed the lighter traffic has a high probability of suffering from starvation. I believe many operating systems can avoid starvation through FIFO and most operating systems consider job priority for example a...
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