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Operating systems exams - multiple choice questions (MCQ) and answers
Operating
Systems MCQ questions and answers – Set 18
1. A memory management unit (MMU) is
responsible for:
(a) Translating a process’
memory addresses to physical addresses
(b) Allocating kernel
memory
(c) Allocating system
memory to processes
(d) All of the above
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Ans : (a)
Answer: (a)
Translating a process’
memory addresses to physical addresses
The MMU is hardware that is part of the microprocessor. It
translates from logical to physical memory locations.
More
on MMU
A
memory management unit translates addresses between the CPU and physical
memory. This translation process is often known as memory mapping because addresses are mapped from a logical space
into a physical space.
The
memory management unit accepts logical addresses from the CPU. Logical
addresses refer to the program's abstract address space but do not correspond
to actual RAM locations. The MMU translates them from tables to physical
addresses that do correspond to RAM.
The
memory management unit (MMU) and associated page tables manage the
translation between code, data, and heap process memory to the underlying
physical memory.
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2. A system uses 32-bit logical
addresses, a 16K byte (214) page size, and 36-bit physical addresses
(64 GB memory). What is the size of the page table?
(a) 218 page
table entries
(b) 222 page
table entries
(c) 214 page
table entries
(d) 24 page
table entries
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Ans : (a)
Answer: (a) 218
entries
Given,
Logical
address = 32 bits
Page
size = 16 KB = 214 bytes
Therefore,
number of bits required for page offset = 14
[Or,
Page offset = log2(page size in bytes) = log2(214) = 14]
Number of bits
in a page = Logical Address - Page Offset = 32
– 14 = 18 bits
Page
table entries = 218 page table entries.
The
physical memory address size does not required here.
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3. During a context switch, the operating
system ______
(a) Modifies some page
table entries for the new process to reflect its memory map
(b)
Switches a page table’s register to select a different page table
(c) Modifies the access
permissions within the page table for the new process
(d) Leaves the page table
untouched since it is a system-wide resource
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Ans : (b)
Answer: (b) Switches a
page table register to select a different page table
Each
process has its own page table.
During
a context switch, the operating system sets the page table base register to the page table for that process.
A
context switch between processes has nothing to do with swapping memory pages
in and out. It simply sets the new process's CPU register context and sets
the page directory to refer to the new process's page tables. The virtual
memory manager is responsible for deciding when to swap pages in and out and
updating the process's page tables to reflect that.
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4. Which one of the following is an
example of a hardware solution to the critical section problem?
(a) Banker’s algorithm
(b) Compare and Shop
(c) Test and Set
(d) Peterson’s algorithm
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Ans : (c)
Answer: (c) Test and Set
Test
and set is a hardware solution to the critical section problem.
- Test
and set is a hardware implementation for testing for the lock and resetting
it to locked. If test shows unlocked, the process may proceed.
- It
acts as an atomic operation
- It
permits Busy waits, Spinning, and Spinlocks.
The other hardware solution is “compare and swap operation”.
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5. When a process is created using the
classical fork() system call, which of the following is NOT inherited by the
child process?
(a) Process address space
(b) Process ID
(c) Open files
(d) Signal handlers
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Ans : (b)
Answer: (b) Process ID
Child
process has its own unique process ID. It will not inherit the process ID of
parent.
What
does the child process inherit from parent?
Environment
settings, open file descriptors, signal handling settings, group IDs, memory
mapped segments, current working directory, resource limits, controlling
terminal, root directory etc.
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