2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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Ques!on 1 (4 points)
Ques!on 2 (4 points)

Which of the following virtual memory implementa!ons does NOT suffer from
external fragmenta!on if a tradi!onally laid-out address space is used?
(Tradi!onally laid out, i.e., how OS/161 has a code, data, and stack segment).
Select all that apply.

dynamic reloca!on
segmenta!on
single-level paging
mul!-level paging
segmenta!on with paging
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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Ques!on 3 (4 points)
Which of the following statements are true about on-demand paging.
Select all that apply.
A system uses mul!-level paging with 2^12 byte pages and 2^4 byte PTEs. The
system uses 64 bit virtual and physical addresses.
How many bits are used for the page offset?
How many PTEs fit on a page?
Give your answer in the form 2^X.
How many bits are needed for the
page number? How many levels
are needed?
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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Ques!on 4 (4 points)
The performance of on-demand paging is on par with address space
preloading.
Page faults are costly because they require a fetch from physical memory.
Page faults are costly because they require a fetch from secondary storage.
LRU is not prac!cal to implement.
The op!mal page replacement algorithm requires knowledge of the future,
and is hence impossible to implement at this point in !me.
The clock algorithm es!mates LRU.
The clock algorithm may loop forever.
Page replacement algorithms could be used for TLB evic!ons or other cache
evic!ons.
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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Ques!on 5 (1 point)
Ques!on 6 (1 point)

On a context switch between processes, the MMU must be updated and the
TLB must be cleared.
True
False

The addrspace structure contains informa!on for the physical and virtual start
addresses along with the size in pages for each of the code, data, and stack
segments.
True
False
A system uses 32 bit virtual and physical addresses. It uses segmenta!on and
has 4 segments in the address space.
How many bits are used for the segment number?
How many bits are used for the
segment offset?
What segment is the following address in?
0xA5A5 A5A5
What is the segment offset (write
your answer in the format 0xDDDDDDDD).
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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PTEs only contain the frame number.
True
False

The bootstrapping problem is solved by the architecture.
True
False

The number of levels in a mul!-level page table depends on the size of virtual
memory, the number of PTEs that fit on a page and the size of physical memory.
True
False

If every entry in a page table is invalid, then it will not be present in the mul!-
level table.
True
False

The use bit is used to determine if a page has been used since the last page
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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fault.
True
False

In a modern opera!ng system, it is feasible that one could change the size of a
segment via a system call.
True
False

If the segment offset is equal to the segment limit, the MMU should throw an
excep!on.
True
False

load_elf is the name of the func!on used to populate an address space in
OS/161.
True
False

In OS/161, the stack segment posi!on and size is fixed.
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True
False

kseg2 is extra space to be used by the kernel, should kseg0 fill up.
True
False

LRU is not directly used in prac!ce.
True
False

On modern computer systems, it is impossible to know the future.
True
False

On-demand paging is always slower than address space preloading.
True
False
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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In dynamic reloca!on or segmenta!on, if the virtual address (or offset) is less
than or equal to the corresponding limit, then the address is valid.
True
False

Segmenta!on solves the external fragmenta!on problem that dynamic
reloca!on suffers from.
True
False

Many opera!ng systems solve the sharing problem by dividing the virtual
address range into two blocks---one for the user, and the other for the kernel.
That way, kernel and user addresses are easily dis!nguishable.
True
False

With a con!guously allocated address space (all segments together), dynamic
reloca!on suffers from internal fragmenta!on.
True
False
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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Dynamic reloca!on is very efficient.
True
False

kseg1 is used in OS/161 for devices. This means that the code used to interact
with things like printers and keyboards lives in kseg1.
True
False

In single-level paging, the number of bits in a page number is the log of the
number of pages in the address space.
True
False

Only leaf nodes of a mul!-level page table contain page-to-frame mappings.
True
False

If an MMU supports segmenta!on via per-segment registers, the minimum
2020-07-19, 7)47 AMQuiz - CS 350 - Spring 2020 - University of Waterloo
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Ques!on 29 (1 point)
number of registers required per segment is 2.
True
False

There are three goals for a virtual memory implementa!on: isola!on, efficiency,
and abstrac!on.
True
False
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