7.16 - daily question - 408

One sentence per day ： Feet on the ground , March forward courageously , The way you walked , Every step counts ！

data structure
1. Two way circular list with leading node L The condition for an empty table is ________( Anhui University 2014 year )
A. L->next = L
B. L = NULL
C. L->next->prior = NULL
D. L->prior = NULL

answer ：A
analysis ： Bidirectional circular linked list L The structure of an empty table is shown in the following figure ,L Of next and prior All point to itself , Only A Options meet conditions .

expand ：
1、 Double linked list is also called double linked list , It's a kind of linked list , It has two pointers in each data node , Direct successor and direct precursor respectively . therefore , Starting from any node in the double linked list , Can easily access its predecessor and successor nodes . In general, we construct a bidirectional circular list .

2、 Circular list is another form of chain storage structure . Its characteristic is that the pointer field of the last node in the table points to the head node , The whole list forms a ring .

computer network
2. The following is true __________( Peking University, 2019 year )
A. Each user of frequency division multiplexing can always occupy all the channel bandwidth
B. Each user of time division multiplexing can always occupy all channel bandwidth
C. Code division multiplexing each user can always occupy all the channel bandwidth
D. Each user of code division multiplexing cannot occupy all channel bandwidth all the time

answer ：C

analysis ：
All users of frequency division multiplexing occupy different bandwidth at the same time ( Frequency bandwidth ) resources .
Time division multiplexing divides time into equal length time division multiplexing frames (TDM frame ). Every time division multiplexing user in every TDM The slot occupying a fixed number in the frame , All users occupy the channel in turn .
Code division multiplexing each user can use the same channel for communication at the same time , Because each user uses different code types specially selected , So there is no interference between users .

operating system
3. About the critical zone , The correct statement is ________( Beijing Jiaotong University 2009 year )
A. Two processes accessing different critical resources do not need to enter the critical area mutually exclusive
B. A critical area is a data area containing critical resources
C. Critical section is a mechanism for process synchronization
D. A critical area is a process or thread that accesses critical resources

answer ：A
analysis ： Two processes that access different critical areas , It is not required to enter the critical zone mutually exclusive .B in , The critical area is the program that accesses critical resources , Not one that contains critical resources - Segment data area ,D Also obviously wrong .C Obviously, the critical zone is not a mechanism for process synchronization .
expand ：
A critical area refers to an access shared resource （ for example ： Shared devices or shared memory ） Of Program fragment , And these shared resources can not be accessed by multiple threads at the same time . When a thread enters a critical section , Other threads or processes must wait （ for example ：bounded waiting Waiting method ）, Some synchronization mechanisms must be implemented at the entry and exit points of critical sections , To ensure that these shared resources are mutually exclusive .

The principle of computer organization
4… The word length of a machine is 32 position , Memory is addressed in half word , After each instruction is taken PC The value of is automatically +2, The instruction length is ______( Beijing university of aeronautics and astronautics 2018 year )
A.16 position
B.32 position
C.64 position
D.128 position

answer ：B
analysis ： Because the memory is addressed by half word , That is, the storage word length is 16 position , And because every time you take out an instruction PC The value of is automatically +2, It indicates that the instruction word length is equal to twice the storage word length , namely 32 position .

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