cs143a quiz 4 homework questions

minimum number of page faults that a program incurs to update all elements

1. bytes per row = # of columns * size of element

2. pages per row = bytes per row / page size in bytes

3. pages = pages per row * # of rows

virtual to physical address formula

Physical address = Segment base + offset

Can offset be greater than length of a segment

No it is an illegal reference

True or False: the first-fit memory allocation algorithm must traverse the entire list of available holes before making an allocation decision?

False, it allocates the first hole that is big enough

In the copy-on-write scheme, can both parent and child processes write to the same shared address space?

False, they get separate writable instances

True or False. two processes can access the same physical memory with different virtual addresses?

True

True or False non-contiguous partitions of physical memory can never be allocated to a single process

False, they can be allocated in systems using paging or segmentation.

page offset bits

page offset bits = log(page size)

number of bits used to represent the page number

Page number bits = total address bits - page offset bits

True or False when paging is used, there is external fragmentation?

true

what is the virtual address space divided into?

Pages

Virtual Address

addresses used by the CPU when accessing memory

What is compaction used for?

Reducing external fragmentation.

Frames

the fixed sized blocks in physical memory used to implement paging

Which of the following is true about segmented paged memory?

Segments are divided into fixed-sized pages

What is a key characteristic of inverted page tables?

They take more time to search the table when a page reference occurs

What is the purpose of the Translation Lookaside Buffer?

To cache translations of virtual addresses to corresponding physical addresses

What is the segment table base register?

A register in MMU that points to the segment table's location in memory

Internal fragmentation

when the memory allocated to a process is larger than the requested memory

Translation

the process of converting virtual addresses to physical addresses

Execute bit

a bit in a page table entry that indicates whether that page's contents can be executed

What is a major advantage of the page buffering algorithm?

It avoids the need to wait for a page to be swapped out by keeping a pool of free frames

What is the concept of thrashing in operating systems?

Excessive page swapping between main memory and disk that leads to a significant decrease in CPU utilization

Why does thrashing occur in an operating system?

the system's physical memory is insufficient to accommodate the working set of all active processes

What best describes the concept of the "working set" of a process?

an approximation of the locality of a process

Which method can be used to measure the working set size of a program?

Checking the reference bits in the page table at fixed intervals

What is a potential disadvantage of using huge page sizes in virtual memory?

Increased wasted space (internal fragmentation) within each allocated memory page

Demand paging

the kernel loads pages of a process into memory only when they are needed

minimum number of page faults that a program incurs to update all elements

1. bytes per row = # of columns * size of element

2. pages per row = bytes per row / page size in bytes

3. pages = pages per row * # of rows

Which performance criterion is used to determine whether a page replacement algorithm is effective?

Page fault rate during program execution

Locality or Working Set

the overall set of pages in a given time frame

Which page table entry bit does the OS use to keep track of pages that have been written to?

Modify bit

Thrashing in a graph

the utilization plummets in high multiprogramming regions

Belady's Anomaly

allocating more frames does not result in less page faults

Step 1 of 80386 Multi-Level Address Translation: How do you parse the raw virtual address?

Convert the address to binary and split it into four 2-bit fields: Segment, Page Directory, Page Table, and Displacement