Confusing knowledge points of software designer examination

One 、 Computer composition and architecture
Easy to confuse 1： primary 、 back 、 The operation of complement
1、 Original code ： The highest bit is the sign bit , The remaining low bits represent the absolute value of the value （0 It means a positive number ,1 A negative number ）.
2、 Inverse code ： The inverse of a positive number is the same as the original , The inverse of a negative number is the bitwise negation of its absolute value （ The sign bits remain the same ）.
3、 Complement code ： The complement of a positive number is the same as the original code , The complement of a negative number is the last digit of its inverse plus 1（ The sign bits remain the same ）.
4、 Shift the code ： The sign bit of complement is reversed bit by bit .
Easy to confuse 2： Comparison of addressing modes
1、 Immediate addressing mode ： The operands are directly in the instruction , Poor flexibility , But the fastest .
2、 Direct addressing mode ： The instruction stores the address of the operands ,.
3、 Indirect addressing ： There is an address in the instruction , This address corresponds to the address of the operands .
4、 Register addressing mode ： Operands are stored in registers , Instruction specifies the register number .
5、 Register indirect addressing mode ： The address of the operands is stored in the register .
Easy to confuse 3： Data transmission mode
1、 Program control （ Inquire about ） The way ： It is divided into unconditional transmission and program query . Simple method , Low hardware overhead , but I/O The ability is not high , serious influence CPU Utilization ratio （ Not to CPU parallel ）.
2、 Program interrupt mode ： Compared with program control , Interrupt mode because CPU The response speed of transmission request is improved without waiting （ But with CPU parallel ）.
3、DMA The way ：DMA The method is to realize high-speed communication between main memory and peripherals 、 Set for batch data exchange ,DMA Mode is more efficient than program control mode and interrupt mode （ But with CPU parallel ）.
Easy to confuse 4： reliability 、 Usability 、 Maintainability
1、 Reliability can be used MTTF/（1+MTTF） To measure .
2、 Availability can be used MTBF/（1+MTBF） To measure .
3、 Maintainability can be used MTTR/（1+MTTR） To measure .
Easy to confuse 5：RISC and CISC

Two 、 data structure
Easy to confuse 1： Sequential storage and chain storage

Easy to confuse 2： Empty string and blank string
1、 Empty string ： The length is zero , Does not contain any characters .
2、 Space string ： A string of one or more spaces . Although a space is a white space character , But it's also a character , When calculating the length of the string, it should be taken into account .
Easy to confuse 3： Substrings and subsequences
1、 Substring ： A sequence of consecutive characters of any length in a string is called a substring . Strings containing substrings are called primary strings . The position of the substring in the main string refers to the first occurrence of the substring , The position of the first character of the substring in the main string . An empty string is a substring of any string .
2、 Subsequence ： A string of “ Subsequence ” Is to extract some characters from this string to get a new string , And do not change their relative position relationship .
Substrings are required to be continuous , The subsequence requires that the relative position is not changed , for example ：ABC The substring of is AB,BC, The subsequence can be AC.

Easy to confuse 2： Summary of common algorithm features

Four 、 Fundamentals of programming language and language processing program
Easy to confuse 1： Compilation and interpretation

Easy to confuse 2： Value passing and address calling

5、 ... and 、 Software Engineering
Easy to confuse 1： Cohesion

Easy to confuse 2： Coupling

Easy to confuse 3： General design and detailed design
1、 Outline design ： Refers to the design of the entire architecture , Design between modules , The corresponding is the integration test of the test .
2、 Detailed design ： It is the internal design of the module , Corresponding to the unit test of the test .
Easy to confuse 4： Software maintenance type
1、 Corrective maintenance ： It refers to correcting the errors that have occurred in the system development stage but have not been found in the system testing stage （ Emphasize correcting mistakes ）.
2、 Adaptive maintenance ： Adaptive maintenance refers to the modification of application software to adapt to the changes of information technology and management requirements （ Emphasize adapting to the environment ）.
3、 Integrity maintenance ： This is a modification to expand functionality and improve performance , It mainly refers to adding some functions and performance features not specified in the system analysis and design stage to the existing software system （ Emphasize perfect functions ）.
4、 Preventive maintenance ： In order to improve the reliability and maintainability of application software , In order to adapt to the future soft / Hardware changes , Preventive new functions should be actively added （ Emphasize prevention in advance ）
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