Postgraduate entrance exam 408 includes data structure, computer network, computer composition principle and operating system four subjects, each of which is the content that programmers should focus on understanding and mastering.

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The exercises come from @Wangdao Weibo

Analysis is my own writing, if there are questions or mistakes please comment to inform, hope to point a big praise 💗

The data structure

If S=’software’, the number of substrings is ___ (Xidian University 2001)

A. 8
B. 37
C. 36
D. 9
Copy the code

Answer and analysis

Answer: B

The substring of 🔊 string is a contiguous segment of the string. If S has 8 characters, there are 9 interval positions. We select 2 of them as the start and end positions of the string, then (where +1 is an empty string) :


C 9 2 = n ∗ ( n – 1 ) 2 + 1 = 9 ∗ 8 2 + 1 = 37 {C} _9 ^ 2 = \ frac {n * (n – 1)} {2} + 1 = \ frac 9 * {8} {2} + 1 = 37

Computer network

TCP/IP ARP belongs to ___ (Zhejiang University 2012)

A. Physical layer B. Network interface layer C. Internet layer D. Transport layerCopy the code

Answer and analysis

Answer: B

🔊 In the TCP/IP model, ARP belongs to the network layer. ARP packets are encapsulated by Ethernet frames rather than IP packets.

Computer composition principle

In virtual memory, address mapping is done by ___ while the program is executing.

A. programmer B. compiler C. loader D. operating systemCopy the code

Answer and analysis

Answer: D

🔊 This question is very simple, but still say the procedure to run the steps:

  1. Compilation: the compiler compiles the user source program to form several target modules
  2. Link: the link program links together a set of compiled target modules and their required library functions to form a complete load module
  3. Load: Loads the load module into memory by the loader. So at runtime, it’s compiled and loaded, and the address mapping is left to the operating system and is transparent to the programmer.

The operating system

(University of Chinese Academy of Sciences, 2013)

A. Increase the CPU interrupt frequency B. Ease the mismatch between CPU and I/O device speeds C. Improve parallelism between CPU and I/O devices D. Relax the limit on interrupt response timeCopy the code

Answer and analysis

Answer: A,

🔊 The main reasons for introducing buffering include:

  • Ease the mismatch between CPU and I/O device speeds
  • Relax the interrupt time limit based on the interrupt frequency to the CPU
  • Improved parallelism between CPU and I/O devices

The buffer technology can reduce the number of interrupts to the CPU and improve the system efficiency.