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Intro to Operating Systems - Exam 2

Terms in this set (42)

Optimal page replacement __.
is used mostly for comparison with other page-replacement schemes
touch
changes the timestamp of a file (or creates a file if given filename does not exist)
mv
moves a file to a new location
cp
copies a file
rm
deletes a file
chmod
changes the permission on a file or directory
mkdir
creates a subdirectory
find
searches a directory and its sub directories for a given file name
TF if a resource-allocation graph has a cycle, the system must be in a deadlocked state.
False
TF The value of a binary semaphore can range only between 0 and 1
True
TF Invoking a synchronized method in Java does not require owing the object lock.
False
TF Race conditions are prevented by requiring that critical regions be protected by locks
True
TF Reentrant code can be shared
True
TF without a mechanism such as an address-space identifier, the TLB must be flushed during a context switch.
True
TF Fragmentation does not occur in a paging system
False
TF There is a 1:1 correspondence between the number of entries in the T:B and the number of entries in the page table
False
What is priority inversion? Name and describe a solution to priority inversion.
Priority inversion: scheduling problem when lower priority processes hold resources needed by a higher priority process

Solution: priority ceiling protocols - a high priority task can be blocked at most once during its execution by lower priority tasks
Explain what fragmentation is in the context of computer memory systems. What is the difference between internal fragmentation and external fragmentation?
Fragmentation: occurs when memory is allocated and returned to system; free memory is broken up into small chunks that are often too small to be useful

External fragmentation: occurs when there is sufficient total free memory to satisfy a memory request, yet memory is not contiguous so it can't be assigned

Internal fragmentation: occurs when a process is assigned more memory than requested and the wasted memory fragment is internal to a process.
Tell whether or not a deadlock exists in the following resource allocation graph. Explain your reasoning.
No because there is circular waiting and p4 can release r2 and then .....
An MMU in a virtual memory system uses a 64-entry, fully associative Translation Lookaside Buffer. If the main memory access time is 13 ns and the T:L lookup time is 3 ns, and the hit Ratio of the TLB is 98%, what is the average time required for a (non-page-faulting) reference to main memory location?
.......
Suppose a process has the following reference string (sequence of page accesses): 1 2 3 4 1 3 4 2 2 4 1 3 1 2. The process of referencing this sequence of pages has a fixed allocation of three page frames. How many page faults would occur under each of the following replacement policies:
A) FIFO B) LRU C) optimal
...............
A given memory system has page size of a 4 KB. If a process reference memory location 6537, calculate the page number and the offset within the page.
........................
A race condition _.
results when several threads try to access the same data concurrently
An instruction that executes atomically _.
executes as a single, uninterruptible unit
Suppose a process using semaphores does a release() operation before executing its critical And an acquire() operation afterward, instead of the other way around. What may happen due to this error?
Multiple processes could be in their critical sections simultaneously
A spinlock _.
does not require a context switch when a process must wait on a lock
_ occurs when a process spends more time paging than executing
Thrashing
A solution to the critical section problem does not have to satisfy which of the following requirements?
atomicity
A(n) _ refers to where a process is accessing/updating shared dATA
critical section
What is the purpose of the mutex semaphore in the implementation of the bounded-buffer problem using semaphores?
It ensure mutual exclusion to the shared buffer.
A calling java thread becomes the owner of a lock when )
It enters a synchronized method
Belady's Anomaly is the observation that ______.
for some PRAs, the page fault rate may increase as the number of allocated frames increases
A deadlocked state occurs whenever __.
every process in a set is waiting for an event that can only be caused by another process in the set
In a system resource-allocation graph, __.
a directed edge from a process to a resource is called a request edge
One necessary condition for deadlock is ______, which states that a process must be holding one resource and waiting to acquire additional resources
hold and wait
To handle deadlocks, operation systems most often __.
pretend that deadlocks never occur
An address generated by a CPU is referred to as a ____.
logical address
Suppose a program is operating with execution-time binding and the physical address generated is 550. The relocation register is set to 250. What is the corresponding logical address?
300
__ is the dynamic storage-allocation algorithm which results in the smallest leftover hole in memory.
Best fit
A(n) __ page table has one page entry for each physical frame of memory.
inverted
Consider a logical address with a page size of 16 KM. How many bits must be used to represent the page offset in the logical address?
14
A(n) __ matches the process with each entry in the TLB
address-space identifier
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