⭐ 題目出自考古題
選擇題 #
🌋1. A race condition ____. #
- (A). results when several threads try to access the same data concurrently
- (B). results when several threads try to access and modify ( 修改 ) the same data concurrently
- (C). will result only if the outcome of execution does not depend on the order in which instructions are executed
- (D). None of the above
💣答案 : (B)
⭐ Race Condition : 多個執行緒或行程同時存取並修改共享資源，結果會依執行順序不同而產生不一致結果的情況。
🌋2. A solution to ( 解決 ) the critical section problem does not have to satisfy ( 不必滿足 ) which of the following requirements? #
- (A). mutual exclusiony
- (B). atomicity ( 原子性 )
- (C). progress
- (D). bounded
💣答案 : (B)
🌋3. How many philosophers may eat simultaneously ( 同時用餐 ) in the Dining Philosophers problem ( 哲學家用餐問題 ) with 5 philosophers? #
- (A). 2
- (B). 3
- (C). 5
- (D). 1
💣答案 : (A)
🌋4. When using semaphores ( 號誌 ), a process invokes the wait() operation before accessing its critical section ( 臨界區之前 ), followed by the signal() operation upon completion of its critical section ( 臨界區工作後 ). Consider reversing the order of these two operations first calling signal(), then calling wait() ( 把順序顛倒過來 ). What would be a possible outcome of this? #
- (A).Starvation is possible.
- (B).Several processes could be active ( 多個行程進入臨界區段 ) in their critical sections at the same time ( 同時 ).
- (C). Deadlock is possible.
- (D).Mutual exclusion is still assured.
💣答案 : (B)
🌋5. A deadlocked ( 死結 ) state occurs ( 發生 ) whenever ____. #
- (A).every process in a set is waiting ( 等待 ) for an event that can only be caused by another process in the set ( 只能由該組中另一個行程」所觸發的事件 )
- (B).a process is unable to release its request for a resource after use
- (C).the system has no available free resources
- (D).a process is waiting for I/O to a device that does not exist
💣答案 : (A)
🌋6. Which of the following statements is true? #
- (A).A safe state may lead to a deadlocked state.
- (B).An unsafe state is necessarily, and by definition, always a deadlocked state.
- (C).An unsafe state ( 不安全狀態 ) may lead to a deadlocked state ( 死結 ).
- (D).A safe state is a deadlocked state.
💣答案 : (C)
🌋7. A _____ could be preempted ( 搶先 ) from a process. #
- (A).mutex lock
- (B).CPU
- (C).semaphore
- (D).file lock
💣答案 : (B)
🌋8. _____ is the method of binding ( 綁定 ) instructions and data to memory performed by most general-purpose operating systems. #
- (A).Load-time binding
- (B).Interrupt binding
- (C).Compile time binding
- (D).Execution time (執行時期) binding
💣答案 : (D)
🌋9. Suppose a program is operating with execution-time binding and the physical address ( 實體位址 ) generated is 300. The relocation register is set to 100. What is the corresponding logical address ( 邏輯位址 )? #
- (A).199
- (B).201
- (C).200
- (D).300
💣答案 : (C)
🚀解釋 :
- \[\text{實體位址 (Physical Address)} = \text{邏輯位址 (Logical Address)} + \text{重定位暫存器 (Relocation Register)}\]
- \[300 = \text{Logical Address} + 100\]
- \[\text{Logical Address} = 300 - 100 = \mathbf{200}\]
🌋10. Assume a system has a TLB hit ratio ( 命中率 ) of 90%. It requires 15 nanoseconds to access ( 存取 ) the TLB, and 85 nanoseconds to access main memory. What is the effective memory access time ( 有效記憶體存取時間 EMAT ) in nanoseconds for this system? #
- (A).176.5
- (B).108.5
- (C).22
- (D).100
💣答案 : (B)
🚀解釋 :
- 情況 1：運氣好 (TLB Hit)
- 過程：查 TLB (15ns) \(\rightarrow\) 找到了！直接去記憶體抓資料 (85ns)。
- 花費時間：\(15 + 85 = \mathbf{100 \text{ ns}}\)
- 情況 2：運氣不好 (TLB Miss)
- 過程： 查 TLB (15ns) \(\rightarrow\) 沒找到… \(\rightarrow\) 去記憶體查 Page Table (85ns) \(\rightarrow\) 拿到地址後，再去記憶體抓資料 (85ns)。
- 重點： Miss 的時候，你需要訪問記憶體 2次 (一次查表，一次抓資料)。
- 花費時間： \(15 + 85 + 85 = \mathbf{185 \text{ ns}}\)
\[EMAT = 0.9 \times (15 + 85) + 0.1 \times (15 + 85 + 85)\]
- Hit 部分：\(0.9 \times 100 = \mathbf{90}\)
- Miss 部分：\(0.1 \times 185 = \mathbf{18.5}\)
- 加總：\(90 + 18.5 = \mathbf{108.5 \text{ ns}}\)
🌋11. _____ is the algorithm implemented on most systems. #
- (A).Least frequently used
- (B).Most frequently used
- (C).LRU
- (D).FIFO
💣答案 : (C)
🌋12. Optimal page replacement ( 最佳頁面置換演算法 ) ____. #
- (A).can suffer from Belady’s anomaly
- (B).requires that the system keep track of previously used pages
- (C).is the page-replacement algorithm most often implemented
- (D).is used mostly for comparison with ( 比較 ) other page-replacement schemes
💣答案 : (D)
⭐ OPT ( Optimal page replacement )需要未來視，在現實世界是不可能做到的，但它是理論上的天花板，所以都是用來評估某個置換演算法。
🌋13. ________ allows the parent and child processes to initially share the same pages ( 相同的頁 ), but when either process modifies ( 修改 ) a page, a copy of the shared page is created. #
- (A).virtual memory fork
- (B).copy-on-write
- (C).zero-fill-on-demand
- (D).memory-mapped
💣答案 : (B)
🌋14. _____ occurs when a process spends more time paging than executing ( 執行 ). #
- (A).Thrashing
- (B).Demand paging
- (C).Memory-mapping
- (D).Swapping
💣答案 : (A)
🌋15. The _____ is an approximation of a program’s locality ( 程式區域性 ). #
- (A).working set
- (B).page fault frequency
- (C).page replacement algorithm
- (D).locality model
💣答案 : (A)