CS 4348 - Exam 2 - Chapter 8

Mix & Match. A. Small Page Size B. Large Page Size 1. increases the page table size 2. increases the likelihood of page faults 3. reduces internal fragmentation 4. more efficient for data transfers

(A,1,3),(B,2,4) Small Page Size Pros: - reduces internal fragmentation - good memory utilization Cons: - more pages per process - increases the page table size Large Page Size Pros: - more efficient for data transfers Cons: - increases the likelihood of page faults

Mix & Match. A. Page Table B. Inverted Page Table 1. Uses one page table entry per virtual page 2. Uses one page table entry per memory frame 3. Can be very large 4. Typically reduces the size of the page table 5. Each process has its own page table 6. All processes are supported by one page table

(A,1,3,5),(B,2,4,6) Page Table 1. Uses one page table entry per virtual page 3. Can be very large 5. Each process has its own page table Inverted Page Table 2. Uses one page table entry per memory frame 4. Typically reduces the size of the page table 6. All processes are supported by one page table

Mix & Match. A. Main Memory B. Virtual Memory 1. Real Memory 2. Program's logical view of memory 3. Can make real memory appear larger 4. Is limited to what is available on the machine

(A,1,4),(B,2,3) Main Memory - Real Memory - Physical Memory on the machine - Limited to whatever memory is available Virtual Memory - Program's logical view of memory - Can be very large, larger than Main Memory - Makes use of disk drive to augment main memory - Can make main memory appear larger than it is

Mix & Match. A. Optimal B. LRU C. FIFO D. Clock 1. Replaces page that has not been referenced for the longest time. 2. Select page whose time to next reference is the longest. 3. Replaces page that has been in memory the longest. 4. Uses circular buffer of frames to find candidates for replacement.

(A,2),(B,1),(C,3),(D,4) Optimal Select page whose time to next reference is the longest. Least Recently Used (LRU) Replaces page that has not been referenced for the longest time. First In First Out (FIFO) Replaces page that has been in memory the longest. Clock Policy Uses circular buffer of frames to find candidates for replacement.

Suppose performance is based on the number of page faults per many references given an increase of frame allocation. Order the following from best to worst. "Best" = less faults "Worst" = more faults A. FIFO B. CLOCK C. LRU D. OPTIMAL

1. Optimal 2. LRU 3. CLOCK 4. FIFO Chapter 8 Slide 50

Describe the process of translating a virtual address to a physical address in a combined segmentation and physical system.

A virtual address maintains Segment Number, Page Number, and an offset. The segment number is added to a segment table pointer and used to index the segment table, fetching the address of a page table for that segment. The page number is then added to the page table address and this is used to index the page table to get the frame number. The frame number is then combined with the virtual address' offset to form the physical address where memory can be accessed. See Chapter 8 Slide 35

Describe the process of translating a virtual address to a physical address in a segmentation system.

A virtual address maintains a virtual segment number and an offset number of bits. The segment number is added to the segment table pointer, to find the location of the base address for that segment from the segment table. The base address of the segment is then added to the offset bits of the virtual address, which forms the physical address of the segment in main memory. See Chapter 8 Slide 33

Which of the following does NOT describe clock policy? A. Attempts to implement FIFO with low overhead B. Sets the use bit to 1 on the first load of page and each time a page is referenced C. Goes through the pages in a circular buffer looking for pages set to 0 to replace D. As it searches, each page with a 1 is set to 0. If all are 1, then all are set to 0.

A. Attempts to implement FIFO with low overhead Clock Policy implements LRU with low overhead

The ___________ determines when a page should be loaded into memory. A. Fetch Policy B. Replacement Policy C. Load Policy D. Placement Policy

A. Fetch Policy

Which replacement scope strategy does NOT make sense? Select all that apply. A. Fixed Allocation, Global Scope B. Variable Allocation, Global Scope C. Fixed Allocation, Local Scope D. Variable Allocation, Local Scope

A. Fixed Allocation, Global Scope This does NOT make sense because it must always replace its own page to keep its fixed allocation size from changing.

With respect to replacement scope strategy, ________ chooses among a process' own resident pages to replace. A. Local replacement B. Global replacement C. Inner replacement D. Outer replacement

A. Local replacement

In adjusting the size of the resident set, ________________ gives a process pages as it runs, possibly according to page fault rates. A. Variable-Allocation B. Dynamic-Allocation C. Static-Allocation D. Fixed-Allocation

A. Variable-Allocation

_________ is the ability of the processor to interrogate simultaneously a number of TLB entries to find a match all at once. A. Blast Mapping B. Associative Mapping C. Direct Mapping D. Brute Force Mapping

B. Associative Mapping

__________ only brings in a page when it is referenced, resulting in high page faults at first, but lower once most needed pages are loaded due to locality. A. Punch Paging B. Demand Paging C. Load Paging D. Prepaging

B. Demand Paging

With respect to replacement scope strategy, ________ chooses among any process' resident pages to replace. A. Local replacement B. Global replacement C. Inner replacement D. Outer replacement

B. Global replacement

All of the following are candidate processes to be suspended to reduce the degree of multiprogramming EXCEPT? A. Lowest Priority B. Highest Priority C. Faulting Process D. Last Process Activated E. Smallest Resident Set F. Largest Process G. Process with the longest remaining execution window

B. Highest Priority

The ___________ replaces the page that is least likely to be referenced in the near future. A. Fetch Policy B. Replacement Policy C. FIFO Policy D. Placement Policy

B. Replacement Policy

Which of the following is NOT true about Page Buffering? A. A replaced page is not lost but reassigned to a free page list or a modified page list. B. The page is physically removed from memory after replacing it. C. The free and modified page lists act as a cache of pages D. Page Buffering reduces the impact of poor replacement

B. The page is physically removed from memory after replacing it. The page is NOT physically removed from memory

_________ occurs when the CPU is spending too much time loading and unloading parts of processes rather than running them. A. Headbanging B. Thrashing C. Race Condition D. Preemption

B. Thrashing

In __________ modified pages are written out to secondary storage ONLY when they are chosen for replacement. A. Demand Writing B. Prewriting C. Demand Cleaning D. Precleaning

C. Demand Cleaning

Which of the following is NOT considered a characteristic of paging and segmentation? A. All memory references are logical addresses that are translated at runtime into physical addresses B. A process may be broken up into many pieces and those pieces need not be contiguous C. It is necessary that all pages or segments of a program be in main memory at the same time

C. It is necessary that all pages or segments of a program be in main memory at the same time It is NOT necessary that this is the case. It is ONLY necessary to have the pieces in memory that are needed.

Which approach to fetch policy will result in efficient use of the disk drive when reading a page? A. Read Paging B. Demand Paging C. Prepaging D. DePaging

C. Prepaging

The principle of locality says _______________. A. Memory can be augmented through disk B. if a cluster of needed segments is in memory, then the program can fetch those segments easier cause they are near each other C. if a cluster of needed pages is in memory, then the program can run for a while without needing more pages loaded

C. if a cluster of needed pages is in memory, then the program can run for a while without needing more pages loaded

Refer to Chapter 8 Slide 49. With respect to the CLOCK illustration, when the subsequence 2 4 5 is introduced, why does the frame pointer go seemingly unshifted?

CLOCK uses circular buffer of frames to find candidates for replacement. 1. It sets the use bit to 1 on the first load of page and each time a page is referenced. 2. It goes through the pages in a circular buffer looking for pages set to 0 to replace. 3. As it searches, each page with a 1 is set to 0. If all are 1, then all are set to 0. In the illustration per Chapter 8 Slide 49, prior to the subsequence 2 4 5 being processed, the frame allocation contains 5*, 3, and 1, and the frame pointer points to the location of page 3. Since page 3 is unset, this page is replaced by 2, which then sets its use bit to 1, shown by 2*. Making the frame allocation contain 5*, 2*, 1. The frame pointer is then shifted to the next unset bit, the location of page 1. When page 4 is being processed from the stream, since the frame pointer has located an unused bit, page 1 is replaced by 4. Making the frame allocation contain 5*, 2*, 4*. The frame pointer is then shifted again, circularly, pointing at the top, at location of page 5. The next page from the stream is 5, but 5 is already located in the frame allocation, hence no fault occurs, and it is simply referenced, thus setting the use bit to 1 again.

Which of the following IS TRUE about the Translation Lookaside Buffer (TLB)? A. Acts as a high-speed cache for process segment tables B. Prioritizes the oldest page table entries C. Caches the pages themselves D. Caches the page table entries

D. Caches the page table entries Translation Lookaside Buffer (TLB) 1. High-speed cache for page tables 2. Contains the page table entries that have been most recently used 3. Does not cache the pages themselves 4. Does cache the page table entries

Which of the following is NOT true about LRU? A. Replaces the page that has not been reference for longest time B. Performs almost as well as the optimal policy due to locality C. Needs a time-stamp for each page on every memory reference D. Easy to implement

D. Easy to implement LRU is HARD TO IMPLEMENT due to the need for time-stamping each page on every memory reference.

In adjusting the size of the resident set, ________________ gives a process a set number of pages within which to operate. A. Variable-Allocation B. Known-Allocation C. Static-Allocation D. Fixed-Allocation

D. Fixed-Allocation

LRU and CLOCK are superior to FIFO, but FIFO can be improved through ______________. A. Frame Locking B. Index Freeing C. Preemption D. Page Buffering

D. Page Buffering

A virtual address in a paging system contains the _______ and offset. A. Frame Number B. Base Address C. Length D. Page Number

D. Page Number

The ___________ determines where a page should be put in memory. A. Fetch Policy B. Replacement Policy C. Put Policy D. Placement Policy

D. Placement Policy

In __________ modified pages are written out to secondary storage BEFORE it is chosen for replacement so that the pages may be written out in batches. A. Demand Writing B. Batch writing C. Batch Cleaning D. Precleaning

D. Precleaning

__________ brings in more pages than the actual page that was referenced due to locality. A. Dynamic Paging B. Demand Paging C. Load Paging D. Prepaging

D. Prepaging

__________ is the portion of a process in main memory at a given time. A. Partition B. Thread C. Ready Set D. Resident Set

D. Resident Set

A virtual address in a segmentation system contains the ______ and offset. A. Length B. Segment Base C. Control Bits D. Segment Number

D. Segment Number

If a combined segmentation and paging scheme is used, the virtual address will contain the ______, ________, and offset. A. Length, Segment Base B. Frame Number, Segment Base C. Segment Number, Frame Number D. Segment Number, Page Number

D. Segment Number, Page Number

The performance of any particular set of paging or combined policies in use depend on all of the following except? A. Memory Size B. Relative Speed of Main & Physical Memory C. Size of Processes D. Number of Processes E. Execution Behavior of Programs F. None of the above

F. None of the above

Refer to Chapter 8 Slide 49. With respect to the FIFO illustration, when the page address 5 is introduced, why does it replace the position of 2?

FIFO = First In First Out FIFO replaces page that has been in memory the longest. In the given page address stream, per Chapter 8 Slide 49, 2 is referenced first, followed by 3, followed by 2 again, followed by 1, before 5 is introduced. Since page 2 has been in memory the longest - being introduced first, then later referenced third - FIFO replacement policy states that it should be replaced. Thus, 5 replaces 2.

True or False? For an inverted page table, a hash function is used to map the frame number of the virtual address onto the inverted page table entry.

False For an inverted page table, a hash function is used to map the PAGE NUMBER of the virtual address onto an inverted page table entry.

True or False? Placement Policy is more restrictive when there are free frames.

False If there are free frames, then it doesn't matter since all frames are the same. LESS restrictive.

True or False? Replacement algorithms aim to replace locked frames.

False Replacement algorithms should NOT attempt to replace a locked frame.

True or False? The fewer the pages, the less processes can be loaded.

False The fewer the pages, the MORE processes can be loaded

True or False? The optimal replacement algorithm can be implemented, but is really inefficient ironically.

False The optimal replacement algorithm CANNOT be implemented.

True or False? Today most operating systems use virtual memory with segmentation.

False Today most operating systems use virtual memory with PAGING or COMBINED APPROACH. SEGMENTATION IS RARELY USED

True or False? A cache hit requires an address to be retrieved from main memory.

False Cache hit => address returned to CPU Cache miss =>address retrieved from Main Memory

True or False? In a Fixed Allocation Local Scope strategy, the working set of pages is considered.

False In a VARIABLE ALLOCATION LOCAL SCOPE strategy, the working set of pages is considered.

True or False? Most issues of paging or segmentation with paging depend on the relative speed of main and physical memory.

False Most issues with paging / combined, depend on PAGING ALGORITHMS and POLICIES in use.

True or False? Pages and segments are determined by the operating system.

False Pages => Determined by the OS Segments => Determined by the programmer

Refer to Chapter 8 Slide 47. Assume that frame 4 and 5 have their use bits set to 1. What would the next frame be to replace?

Frame 8 The clock policy shifts its next frame pointer around seeking for the frame with a use bit of 0. Once it is found, it replaces that frame's page and sets its use bit to 1. For each use bit that is already 1, as the frame pointer rotates, their use bits will become 0. Under the assumption that frames 4 & 5 have their use bits set to 1, then by the illustration on Chapter 8 Slide 47, the frames: 2,3,4,5,6,7 will all be traversed and their use bits flipped to 0. Then the only 0 that remains is in frame 8, this will be the frame whose page is replaced.

Describe the process of translating a virtual address to a physical address in a paging system.

In a paging system, the virtual address has a page number and an offset. The page number acts as an index to the page table where it finds the frame number, and the offset is then added to that frame number to create the physical address. See Chapter 8 Slide 13

Describe the process of translating a virtual address to a physical address in a two-level paging system.

In a two-level paging system, a 32-bit virtual address is maintained. The 1st 10-bits are added to the root page table pointer to get the portion of the root page table necessary. The 2nd 10-bits are added to the returned page location from the root page table to find the location of the page number in the page table. The remaining 12-bits are then added to the frame number to create the address. See Chapter 8 Slide 17

Refer to Chapter 8 Slide 49. With respect to the LRU illustration, when the page address 5 is introduced, why does it replace the position of 3?

LRU = Least Recently Used LRU replaces the page that has not been referenced for the longest time. In the given page address stream, per Chapter 8 Slide 49, 2 is referenced first, followed by 3, followed by 2 again, followed by 1, before 5 is introduced. When 5 is introduced, there is no more space to place it somewhere, so a fault occurs initially, then it takes over the position of 3. 5 takes over the position of 3, because 3 was the page that had not been referenced the longest; since there are only three frames available and 2, 1, 5 was the most recent reference stream.

Refer to Chapter 8 Slide 57. With respect to the second occurrence of the page reference 24, why are the columns with window size of 4 and 5 blank?

The working set strategy keeps the set of pages that have been referenced in the previous delta units. In the illustration, per Chapter 8 Slide 57, see that the columns with the window size (delta = 2, 3, 4, 5) corresponds to the number of page references that can be kept in that window. So, in the case of the second reference to 24, in the columns with the window sizes of 4 and 5, see that 24 is already referenced in the previous 4 and 5 units respectively. Since this is the case, 24's reference in the working set is replaced with the new reference at the end of the window. As seen when inserting 17, see that 24 appears to its left for window sizes 4 & 5.

True or False? An implication of loading only part of a program into memory is that a process can be much larger than main memory and still be run.

True

True or False? If a process tries to access memory outside of its resident set, a fault will occur interrupting the process.

True

True or False? Too few pages results in high page faults

True

True or False? Too few processes running at a time, means that the CPU may not be utilized enough.

True

True or False? Too many pages reduces the number of processes and doesn't reduce page faults noticeably.

True

True or False? Too many processes running at a time, means that the Thrashing may occur due to too few pages per process in memory.

True

True or False? The page fault rate depends on the size of the page and the number of frames allocated to a process.

True As page size grows, locality is weakened, more faults will occur until the page size begins to approach the size of the entire process. If the whole process is in memory, then page faults will be zero. But if only one page is in memory and new page requests are made, there will be page faults for each request. See Chapter 8 Slide 30-31