全国计算机等级考试四级笔试试题一（下）
A) 相邻实体 B) 对等实体 C) 传输实体 D) 通信实体
(52) 在OSI参考模型中,两个(N)层实体之间交换的数据单元称之为(N)协议数据单元,记做(N)PDU。(N)PDU是由两部分组成:(N)PCI与 ____。
A) (N+1)IDU B) (N+1)SDU C) (N)SDU D) (N)IDU
(53) 一个数据源产生8bit的ASCII字符(含1bit校验位),通过一条64Kbps的线路进行数据传输。指出在以下数据传输方式中,哪一种方式的有效数据传输速率可以达到最高? ____。(2分)
A) 采用面向字符型传输协议,每个数据帧包括24B的控制字段与128B的信息字段
B) 除信息字段长度为256B外,其它条件同A)
C) 采用面向比特型传输协议,每个数据帧包括12B的控制字段与64B的信息字段
D) 除信息字段长度为128B外,其它条件同C)
(54) 在面向比特型数据链路层协议HDLC中,帧格式中的哪个域既可以用于流量控制,又可以实现对发送帧的捎带确认?____。（2分）
A) 无编号帧的M域 B) 信息帧的N(S)域
C) 监控帧的S域 D) 信息帧的N(R)、N(S)域
(55) IEEE802.5标准规定令牌环网采用 ____。
A) 多令牌协议
B) 单令牌协议
C) 随机访问协议
D) HDLC协议
(56) 在局域网中,以下哪种传输介质既可以用于物理层10BASE-T协议,又可以适用于100BASE-T协议? ____。
A) 同轴电缆 B) 3类非屏蔽双绞线
C) 5类非屏蔽双绞线 D) 光纤电缆
(57) 如果两个局域网LAN A与LAN B互连,它们的传输层协议不同,而其它层协议均相同, LAN A与LAN B的互连设备应该选择____。
A) repeater B) bridge C) router D) gateway
(58) CCITT推荐的用于多个X.25网络互连的协议为____。
A) X.400 B) X.75 C) X.121 D) X.21
(59) 城市地区网(MAN)主要使用的技术是交换多兆位数据服务SMDS、分布队列双总线DQDB和____。
A) FDDI B) CSMA/CD C) Token Bus D) Token Ring
(60) 在计算机集成制造系统(CIMS)中,存在着办 公自动化(OA)与生产过程控制(MC)两种环境,它们对网络通信的要求也不相同。在CIMS环境中,根据MAP/TOP协议选择局域网协议标准时，应采用以下哪种方案? ____。(2分)
A) 全部采用802.3协议标准
B) OA采用802.3协议标准,MC采用802.4协议标准
C) OA采用802.3协议标准,MC采用802.5协议标准
D) 全部采用HDLC协议标准
(61) An instrucion that uses indirect addressing must contain an address of memory where____．
A) data is stored B) another address is stored
C) a page fault is addressed D) a pepeline stall will be executed
(62) Let R be a binary relation on a set S such that for each x,y,z∈S, if xRy and xRz then y =z. Which of the following must be true? ____．(2分)
A) R is anti-symmetric B) R is transitive
C) R is an equivalence relation D) R is a function
(63) If p and q are Boolean variables, which of the following formulas is (are) tautological?____．
Ⅰ. (┐p→q)↔ (p∨q)
Ⅱ. ((p→q))∧(q→r))→(p→r))
A) none B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
(64) Which of the following statements is (are) true? ____．
Ⅰ. The number of cyclic subgroups of the additive group of integers is infinite.
Ⅱ. The number of cyclic subgroups of the additive group of real numbers is infinite.
A)&nb sp;Neither B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
Questions 65- 66 refer to the space requirements of different methods of storing graphs. The choices for these questions are combinations of the following statements.
Ⅰ. The space required depends on the number of vertices.
Ⅱ. The space required depends on the number of edges.
(65) When the adjacency matrix method is used to store a graph, which of the statements is (are) true? ____．
A) None B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
(66) When the adjacency list method is used to store a graph, which of the statements is (are) true?____．
A) None B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
Questions 67-68 are based on the following information,
A hash table with hash function
h1(k)=k mod 13
is shown below.
0 1 2 3 4 5 6 7 8 9 10 11 12
35 33 48 25
Collision is resolved using the hash function h2(k)=(k mod 11)+1.
(67) How many key comparisons occur in searching for key 35 in the given hash table?____． (2分)
A) 0 B) 1 C) 2 D) 3
(68)& If a new key 67 is inserted into the given hash table, what will be its address?____． (2分)
A) 3 B) 4 C) 5 D) 6
(69) Suppose the contents of the DOS IF1.BAT file on the hard disk is as follows.
@ECHO OFF
MEM>FILE1
SORTFILE2
DEL FILE1
@DATE
@TIME
IF EXIST %1 ECHO % IF FOUND
If all of the commands are successfully executed after IF1 FILE1 is
typed, then the screen displays?____．
A) None B) Date and time C) FILE1 IS FOUND D) FILE2 IS FOUND
(70) If the files in the current directory are
aac, abc, acb,acc, aca, ao, al, a2, ab, ac, aa,
and the command ls a?[bc] is executed, how many files will be listed?____． (2分)
A) 3 B) 4 C) 5 D) 6
(71) In order to append a standard output to an existing file, which of the following operators is used in the UNIX system? ____．
A) | B) & C) > D) >>
(72) Consider the following figure, where the shaded parts represent already assigned blocks of memory, and the unshaded parts represent free blocks. (2分) If there is a request for 40KB of memory and the best-fit algorithm is used, then the beginning address of memory that is allocated in response to the request is ____. A) 100KB B) 190KB C) 330KB D) 410KB
(73) On a certain disk, there are 200 tracks, numbered 0-199, the current position of the disk head is track 53. If the shortest-seek-time-first scheduling algorithm is used when the tracks
98, 183, 37, 122, 14, 124, 65, 67
are requested, then the head-moving sequence that results will be (2分)
A) 65, 67, 37, 14, 98, 122, 124, 183
B) 65, 67, 37, 98, 122, 124, 183, 14
C) 65, 67, 98, 122, 124, 183, 37, 14
D) 98, 183, 37, 122, 14, 124, 65, 67
(74) Whant operation on relations R and S produces the relation shown below?____.
{tuple│tuple∈R۸tuple∈\ S}
A) Union B) Difference C) Intersection D) Division
(75) When embedding SQL in a C language program, the prefix that should be added to all SQL statements in order to distinguish SQL statements from the host language statements is____.
A) ： B) EXEC C) EXEC SQL D) SQL
(76) In the ORACLE system,sets of SQL statements and control flow statements that have been named,compiled,and stored tn the database are referred to as stored____.
A) batches B) procedures C) triggers D) transactions
(77) Which of the following statements about object oriented databases is NOT correct? ____. (2分)
A) Each object has a unique object identity in the system.
B) Encapsulation and inheritance are two important features of object oriented databases.
C) A subclass can inherit the attributes and methods of all its superclasses.
D) A superclass includes the attributes and methods of all its subclasses.
(78) In the design phase of software engineering, decomposition of the program into modules should follow the principles of ____.
A) low cohesion with low corpling B) low cohesion with high coupling
C) high cohesion with low coupling D) high cohesion with high coupling
(79) Specifications for software should contain&nbs p;several components, e.g., specifications of
information flow,
user interface,
functional requirements, and
design constraints.
Two other important components are specifications of the____. (2分)
A) methods of testing and ways to obtain quality assurance
B) criteria for testing and ways to obtain quality assurance
C) methods of testing and criteria for function assurane
D) criteria for testing and methods of function assurance
(80) Which of the following statements about testing software with data is (are) true?____.
I. The primary purpose of such testing is to find errors.
II. Such testing can demonstrate the existence of errors but cannot
demonstrate the absence of errors.
A) Neither B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
(81) The type of testing done during software implementation and beforemodule integration is called ____.
A) unit testing B) beta testing
C) system testing D) acceptance testing
(82) Which of the following is (are) true about software portability? ____.
I. Using a high-level language that conforms to an ISO standardguarantees portability across the range of machines that support the language.
II. Portability is guaranteed across all machines that have the same instruction set and operating system. (2分)
A) Neither B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
(83) A memory-memory, machine instruction for a certain machine has the following format.
(Such an instruction is similar to a register-register instruction
except that the operands are displaced addresses in memory.)
opcode meml displ1 mem2 displ2
Which of the following could be an assembly lanuage instruction that would be translated into a memory-to-memory instruction for this machine? ____.
A) ADD 10(R1), 20(R2) B) ADD(10R1), (20R2)
C) ADD R1, 10(R2), 20 D) ADD R1, 10, 20(R2)
(84) In a certain cache system, the modified cache block is written to main memory only when the block is replaced. All of the following are used to describe this policy EXCEPT____.
A) store-in B) write-back C) copy-back D) write-through
(85) When an amount of memory is requested that is less than the size of a page, but a full page is allocated, the r esulting waste of memory is called ____.
A) external fragmentation B) internal fragmentation
C) inaccessible page faults D) inaccessible garbage
(86) The time that the CPU spends on a given program can be computed using all of the following expressions EXCEPT ____. (2分)
A) (CPU clock cycles for the program)*(clock cycle time)
B) CPU clock cycles for the program
clock rate
C) (Instruction count)*CPI
clock rate
D) (CPU clock cycles for the program)*CPI
clock rate
(87) The methods used in Asynchronous Transfer Mode (ATM) are switch technology and which of the following is used to describe this mode?____.
A) cell exchange B) packet exchange
C) message exchange D) information exchange
(88) In a data communication system, the transport media with the widest frequency band and best reliability is the ____.
A) telephone line B) coaxial cable
C) radio channel D) fiber optic cable
(89) Which of the following statements about the Internet is (are) true?____. I. It is possible to have multiple names corresponding to the same IP address. II. All host names must be registered with an Internet-wide central registry.
A) Neither B) Ⅰ only C) Ⅱ only D) Ⅰ and Ⅱ
(90) According to the principle of CRC calculation, given a frame-bit series M =11100111 and the multiple-term formula, frame-bit series generated by the CRC G =110011, then the CRC is ____.(2分)
A) 111101 B) 00011 C) 11010011 D) 1101001
二、论述题(两个论述题可任选其一,并只选其一,多选无效,满分30分。)
论述题 1
局域网是当前计算机网络研究与应用的一个热点,而符合IEEE 802.3标准的传统Ethenet(MAC层采用CSMA/CD方法,物理层采用 10BASE-T标准)应用最为广泛。随着网络应用的发展,以及大型信息系统与多媒体技术的应用,人们对局域网性能提出了越来越高的要求,出现了符合 100BASE-T标准的Fast Ethernet、交换局域网Switching LAN与ATM等高速局域网产品。尽管高速局域网技术发展十分迅速,但是Ethernet仍然会被广泛地使用。今后的网络应该是传统Ethernet、FastEthernet LAN与ATM共存的结构。因此,研究 Ethernet的基本工作原理、优点与缺点,讨论高速局域网络发展的趋势与特点,对我们学习和掌握局域网应用技术是十分重要的。
(1) 请用Ethernet发送与接收流程框图说明CSMA/CD介质访问控制方法的基本工作原理。(15分)
(2) 为什么说CSMA/CD属于共享介质、随机争用型的介质访问控制方法?这种方法主要缺点是什么? (5分)
(3) 你认为Fast Ethernet与ATM、Switching LAN是从哪两个方面改进了传统的Ethernet?它们各有什么优缺点? (10分)
论述题 2
进程通信就是进程之间进行信息交换。系统中各进程异步执行,但有些进程之间必须保持一定的联系,以便协调一致地完成指定任务。这种联系就是通过交换一定数量的信息来实现的。
消息缓冲通信技术是一种高级通信机制,由Hansen首先提出。其基本思想是:根据"生产者－消费者关系"原理,利用公共消息缓冲区实现进程之间的信息交换。
(1) 试叙述高级通信机制与低级通信机制P、V原语操作的主要区别。(5分)
(2) 试叙述解释消息缓冲通信技术的基本原理。 (10分)
(3) 消息缓冲通信机制中提供发送消息原语。Send(receiver,a)和接收消息原语Receive(a)。调用参数a分别表示发送消息的内存区首地址或接收进程的内存消息区首地址。试设计相应的数据结构,并用P、V操作原语实现Send和Receive原语。 (15分)