Computer Science Previous Year Questions (page 5)

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Referential integrity requires every foreign key value in the referencing relation to appear as a key value in the referenced relation.

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All three statements are true properties of a binary search tree, so none of them is false.

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Y = AB + BC + AC is a sum (OR) of product (AND) terms, so it is in sum-of-products (SOP) form.

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The canonical forms are sum of minterms (SOM, or canonical SOP) and product of maxterms (POM, or canonical POS).

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The circuit gives A + B from the OR gate, then three AND gates in turn multiply it by C, D and E. So Y = C(A + B)DE, with E not inverted.

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Boolean algebra is used in designing digital computers, in building logic symbols and gates, and in switching circuit theory, so more than one option applies.

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The control unit generates control signals that direct the ALU, memory and I/O units.

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Digital clocks at stations show digits on seven-segment displays, which are driven by seven-segment (BCD-to-7-segment) decoders.

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Optical fiber carries data as light, so it is immune to electromagnetic interference. Twisted pair and coaxial cable carry electrical signals that interference can affect.

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In a star topology every device is connected to a central hub or switch, which controls the communication.

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The World Wide Web is the collection of hypertext documents (web pages) on the Internet that are linked by hyperlinks.

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When an IPv6 header is translated to IPv4, the flow label is ignored. Using it is not part of the procedure, whereas extracting the rightmost 32 bits and dropping the priority are.

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Giving every user full access rights lets anyone change or delete data, which breaks integrity. Locks and anti-theft devices protect the system.

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The MAC sublayer handles functions that depend on the medium, such as framing and access control for Ethernet or Wi-Fi. LLC is independent of the medium.

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Peer-to-peer is a network architecture (model), not a topology. Ring and bus are physical topologies.

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When a mail server sends mail to another mail server, it acts as an SMTP client and the receiving server acts as the SMTP server.

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An IPv6 address is 128 bits long. None of the listed sizes (32, 64, 256) is right; 32 bits is IPv4.

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ios::trunc discards the contents of an existing file when it is opened, cutting its length to zero.

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The TCP/IP host-to-host (transport) layer matches the OSI transport layer and provides TCP and UDP.

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Official BPSC final answer key: (D). Note: by the usual reading only statements 2 and 3 are correct, i.e. option (B).

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Ping (Packet InterNet Groper) uses ICMP echo messages to report packet loss and round-trip time. It does not check ports.

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The function takes a float* and a char** and returns an int**, so the correct declaration is int **fun(float *, char **).

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Each party keeps its own private key secret. In public-key encryption, the receiver decrypts with the private key that only the receiver holds.

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factorial(a + 1) makes the argument grow (3, 4, 5, ...), so a > 1 is never false. The recursion never ends, the stack overflows, and the program crashes with a segmentation fault.

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A pure object-oriented language must support encapsulation, inheritance and polymorphism (along with abstraction and objects), so all three are required.

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Both (B) and (C) are valid: class derived : access base { }; and, without an access specifier, class derived : base { }; where the default is private for classes.

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std::is_array<T> (in <type_traits>) checks whether a given type is an array type, returning true or false.

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A class is a blueprint, and an object is an instance of its class. The reverse statement is wrong.

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A class becomes abstract when it has at least one pure virtual function, for example virtual void f() = 0;. Such a class cannot be instantiated.

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All three statements are true. C++ does static type checking at compile time and dynamic checking with RTTI and dynamic_cast, and member functions can be declared const.

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Data hidden inside the classes shows encapsulation, and topper deriving from student with public shows inheritance. There is no overloading or overriding, so polymorphism is not shown.

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Computer chips are made mainly from silicon, a semiconductor used for transistors and integrated circuits.

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The CPU is called the brain of the computer because it carries out all instructions, performs calculations in the ALU and controls every other unit through the control unit.

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Intel 8085 (1976) is an 8-bit microprocessor. 8-bit chips such as the 8008, 8080 and 8085 make up the second generation, after the 4-bit 4004 of the first generation.

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The third generation consists of 16-bit processors such as the Intel 80286. Its 24 address lines can address 2²⁴ bytes, which is 16 MB of memory.

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A microprocessor is a complete CPU (ALU, control unit and registers) on one integrated circuit. A microcontroller is different because it also puts memory and I/O on the chip.

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A microcontroller puts a CPU, RAM, ROM and I/O ports on a single chip, so it is a complete computer on one chip. A microprocessor holds only the CPU.

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A joystick is a lever that can move in any direction, and it is the standard input device for playing video games. Mice and trackballs are general pointing devices.

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ROM is non-volatile and read-only, so it stores fixed software such as firmware and the BIOS that is not normally updated. SRAM and DRAM are volatile working memory.

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A CD drive reads and writes the disc with a laser beam, which is why it is an optical drive. A hard disk uses magnetic heads, and RAM is electronic.

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An assembler translates assembly-language mnemonics into the equivalent machine code. A compiler works on high-level languages, and a linker joins object files together.

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A compiler translates the whole high-level program into machine code (object code) in one go. An assembler handles assembly language, and a loader loads programs into memory.

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An interpreter translates and executes a high-level program one statement at a time. A compiler, by contrast, translates the whole program at once.

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Oracle is a database management system (RDBMS), not an operating system. Linux and Windows are operating systems.

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An operating system runs directly on the hardware, manages its resources and provides the platform on which other software runs. System software is a wider category that also includes utilities and translators.

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Scandisk (which checks a disk) and Format (which prepares a disk) are system tools or utilities. A folder is only a container for organising files.

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Shift + Delete deletes a file permanently and skips the Recycle Bin. Delete on its own moves the file to the Recycle Bin.

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A digital computer has three main parts: the CPU for processing, memory for storage, and I/O devices for input and output. The ALU is part of the CPU, so option (B) is not right.

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FFFF in hex is 65535, so the addresses run from 0000 to FFFF. That is 65536 = 2¹⁶ locations, which is 64K.