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

The input sequence of a stack is ABCD, and the following four sequences that cannot be its output sequence are ____ (Beihang University 2000)

A. acbd
B. bcda
C. cdba
D. dcab
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Answer and analysis

Answer: D

🔊 stack feature is the first out, we eliminate one by one.

D) ABC has been added to the stack. A cannot be removed from the stack before B.

Computer network

Traditional Ethernet sends data using Manchester encoding, the bandwidth occupied ____.

A. the same as the original baseband signal b. half as the original baseband signal C. twice as much as the original baseband signal D. Four times the original baseband signalCopy the code

Answer and analysis

Answer: C

🔊 Manchester code: in the middle of each element level jump, a jump in the middle of the both as the clock signal, and as the data signal, because the Manchester coding each element of the middle time appear a level conversion, can see from Manchester coding waveform figure other band width of the baseband signal is the original two times, so choose C.

For example, the binary number 10011010 can be expressed as follows. In the figure, the code element is divided into two equal intervals, with the first high and the second low being 1 and the opposite being 0:

Computer composition principle

In the common centralized bus arbitration mode, the most sensitive mode to circuit is ____ (Beihang University 2015)

A. chain query B. counter timed query C. independent request D. terminal queryCopy the code

Answer and analysis

Answer: A,

🔊 can be seen from the name, chain query, once the chain is broken, there will be A fault, the circuit is the most sensitive.

The operating system

In a uniprocessor system, if there are 12 processes at the same time, the maximum number of processes in the ready queue is ____ (University of Electronic Science and Technology of China 2012)

A. 1
B. 9
C. 10
D. 11
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Answer and analysis

Answer: D

🔊 In a uniprocessor system, as long as there are processes on the ready queue, there must be one process in the execution queue that has obtained processor resources. Therefore, the ready queue is 12-1=11 at most, so choose D.