3.4. System software
A subsection of Computer Science, 9608, through 3. Advanced Theory
Listing 10 of 52 questions
A number of processes are being executed in a computer. Explain the difference between a program and a process. A process can be in one of three states: running, ready or blocked. For each of the following, the process is moved from the first state to the second state. Describe the conditions that cause each of the following changes of the state of a process: From running to ready From ready to running From running to blocked Explain why a process cannot be moved from the blocked state to the running state. Explain the role of the high-level scheduler in a multiprogramming operating system.
9608_w15_qp_31
THEORY
2015
Paper 3, Variant 1
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A number of processes are being executed in a computer. A process can be in one of three states: running, ready or blocked. For each of the following, the process is moved from the first state to the second state. Describe the conditions that cause each of the following changes of state of a process: From blocked to ready From running to ready Explain why a process cannot move directly from the ready state to the blocked state. A process in the running state can change its state to something which is neither the ready state nor the blocked state. Name this state. Identify when a process would enter this state. Explain the role of the low-level scheduler in a multiprogramming operating system.
9608_w15_qp_32
THEORY
2015
Paper 3, Variant 2
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A number of processes are being executed in a computer. Explain the difference between a program and a process. A process can be in one of three states: running, ready or blocked. For each of the following, the process is moved from the first state to the second state. Describe the conditions that cause each of the following changes of the state of a process: From running to ready From ready to running From running to blocked Explain why a process cannot be moved from the blocked state to the running state. Explain the role of the high-level scheduler in a multiprogramming operating system.
9608_w15_qp_33
THEORY
2015
Paper 3, Variant 3
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A computer operating system (OS) uses paging for memory management. In paging: • main memory is divided into equal-size blocks, called page frames • each process that is executed is divided into blocks of the same size, called pages • each process has a page table that is used to manage the pages of this process The following table is the incomplete page table for a process X. Page Presence flag Page frame address Additional data When a particular page of the process is currently in main memory, the Presence flag entry in the page table is set to 1. If the page is not currently present in memory, the Presence flag is set to 0. The page frame address entry for Page 2 is 245. State what the value 245 could represent. Process X executes until the next instruction is the first instruction in Page 4. Page 4 is not currently in main memory. State a hardware device that could be storing this page. When an instruction to be accessed is not present in main memory, its page must be loaded into a page frame. If all page frames are currently in use, the contents of a page frame will be overwritten with this new page. The page that is to be replaced is determined by a page replacement algorithm. One possible algorithm is to replace the page that has been resident in main memory for the longest time. Give the additional data that would need to be stored in the page table. Complete the table entries below to show what happens when Page 4 is swapped into main memory. Assume that Page 5 is the one to be replaced. In the final column, give an example of the data you have identified in part . Page Presence flag Page frame address Additional data An alternative algorithm is to replace the page that has been used least. Give the different additional data that the page table would now need to store. In the following table, complete the missing data to show what happens when Page 3 is swapped into main memory. Assume that Page 1 is the one to be replaced. In the final column, give an example of the data you have identified in part . Page Presence flag Page frame address Additional data Explain why the algorithms given in part may not be the best choice for efficient memory management. Longest resident Least used
9608_w16_qp_31
THEORY
2016
Paper 3, Variant 1
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A computer operating system (OS) uses paging for memory management. In paging: • main memory is divided into equal-size blocks, called page frames • each process that is executed is divided into blocks of the same size, called pages • each process has a page table that is used to manage the pages of this process The following table is the incomplete page table for a process, Y. Page Presence flag Page frame address Additional data State two facts about Page 5. Process Y executes the last instruction in Page 5. This instruction is not a branch instruction. Explain the problem that now arises in the continued execution of process Y. Explain how interrupts help to solve the problem that you explained in part . When the next instruction is not present in main memory, the OS must load its page into a page frame. If all page frames are currently in use, the OS overwrites the contents of a page frame with the required page. The page that is to be replaced is determined by a page replacement algorithm. One possible algorithm is to replace the page which has been in memory the shortest amount of time. Give the additional data that would need to be stored in the page table. Complete the table entry below to show what happens when Page 6 is swapped into main memory. Include the data you have identified in part in the final column. Assume that Page 1 is the one to be replaced. In the final column, give an example of the data you have identified in part . Page Presence flag Page frame address Additional data …………. ……… …… …………………….…… Process Y contains instructions that result in the execution of a loop, a very large number of times. All instructions within the loop are in Page 1. The loop contains a call to a procedure whose instructions are all in Page 3. All page frames are currently in use. Page 1 is the page that has been in memory for the shortest time. Explain what happens to Page 1 and Page 3, each time the loop is executed. Name the condition described in part .
9608_w16_qp_32
THEORY
2016
Paper 3, Variant 2
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A computer operating system (OS) uses paging for memory management. In paging: • main memory is divided into equal-size blocks, called page frames • each process that is executed is divided into blocks of the same size, called pages • each process has a page table that is used to manage the pages of this process The following table is the incomplete page table for a process X. Page Presence flag Page frame address Additional data When a particular page of the process is currently in main memory, the Presence flag entry in the page table is set to 1. If the page is not currently present in memory, the Presence flag is set to 0. The page frame address entry for Page 2 is 245. State what the value 245 could represent. Process X executes until the next instruction is the first instruction in Page 4. Page 4 is not currently in main memory. State a hardware device that could be storing this page. When an instruction to be accessed is not present in main memory, its page must be loaded into a page frame. If all page frames are currently in use, the contents of a page frame will be overwritten with this new page. The page that is to be replaced is determined by a page replacement algorithm. One possible algorithm is to replace the page that has been resident in main memory for the longest time. Give the additional data that would need to be stored in the page table. Complete the table entries below to show what happens when Page 4 is swapped into main memory. Assume that Page 5 is the one to be replaced. In the final column, give an example of the data you have identified in part . Page Presence flag Page frame address Additional data An alternative algorithm is to replace the page that has been used least. Give the different additional data that the page table would now need to store. In the following table, complete the missing data to show what happens when Page 3 is swapped into main memory. Assume that Page 1 is the one to be replaced. In the final column, give an example of the data you have identified in part . Page Presence flag Page frame address Additional data Explain why the algorithms given in part may not be the best choice for efficient memory management. Longest resident Least used
9608_w16_qp_33
THEORY
2016
Paper 3, Variant 3
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A computer process can be in one of three states: running, ready or blocked. Explain how the processes are affected when the following events take place. The running process needs to read a file from a disk. The running process uses up its time slice. State the conditions that are necessary for a process to move from the ready to the running state. State the conditions that are necessary for a process to move from the blocked to the ready state. Give three reasons why process scheduling is needed.
9608_w18_qp_31
THEORY
2018
Paper 3, Variant 1
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A computer process can be in one of three states: running, ready or blocked. Explain how the processes are affected when the following events take place. The running process needs to read a file from a disk. The running process uses up its time slice. State the conditions that are necessary for a process to move from the ready to the running state. State the conditions that are necessary for a process to move from the blocked to the ready state. Give three reasons why process scheduling is needed.
9608_w18_qp_33
THEORY
2018
Paper 3, Variant 3
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An operating system (OS) uses a memory management technique called paging. Explain what is meant by the following terms. Page Page frame Page table Explain why an operating system needs to use scheduling algorithms. State what is meant by an interrupt. For a computer system using multi-programming, the low-level scheduler decides which process will get next use of the processor. One algorithm could be a round-robin, which means every process gets use of the processor in sequence for a fixed amount of time (time-slice). For a round-robin algorithm, five processes are currently loaded and get the use of the processor in the sequence: JOB21 – JOBSS – JOBPT – JOB32 – JOB42, then return to JOB21 Process JOB32 has just completed its time-slice. The following paragraph describes what happens next. Complete the paragraph by inserting the missing processes. Interrupt received from the low-level scheduler. Save all register contents for . Copy the saved registers for to the CPU. The processor will now process .
9608_w19_qp_31
THEORY
2019
Paper 3, Variant 1
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Questions Discovered
52