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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Analysis is my own writing, if there are questions or mistakes please comment to inform, hope to point a big praise 💗
The data structure
To design a recursive function press n! = n * (n – 1)! To calculate n! , its time complexity is ___ (Nankai University 2013)
A. O(log2n)
B. O(n)
C. O(n^2)
D. O(n!)
Copy the codeAnswer and analysis
Answer: B
🔊 The recursive function decreases in size by 1 each time, and the result is linear.
Computer network
The network is responsible for error control and flow control in which of the following transport modes are used, and the packets are delivered in sequence.
A. circuit switching B. packet switching C. virtual circuit packet switching D. datagram packet switchingCopy the codeAnswer and analysis
Answer: C
🔊 Among the four types of switching, only the virtual circuit can provide reliable transmission, because the virtual circuit needs to establish a logical path in advance to ensure the correct and orderly arrival of packets.
Computer composition principle
Periodic appropriation is often used in ___ (Beihang University 2017)
A. I/O of program query B. I/O of program interrupt C. I/O of DMA D. Channel mode input and outputCopy the codeAnswer and analysis
Answer: C
🔊 Because DMA I/O devices communicate with memory without passing through the CPU, memory is accessed simultaneously. To use memory efficiently, periodic appropriation is used.
In DMA mode, the I/O device has a higher priority than the CPU, because data may be lost if data is not accessed immediately. In this case, the I/O device appropriates one or more cycles.
The operating system
The two most important features of an operating system are __
A. concurrency and virtuality B. parallel distribution and sharing C. sharing and asynchro D. Sharing and virtualityCopy the codeAnswer and analysis
Answer: B
🔊 remember.