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GCE A/L Information & Communication Technology study materials
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GCE A/L Information & Communication Technology practice questions

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Question 1Information and Communication Technology: concepts, evolution and impact on society

Which statement best describes the relationship between data, information and knowledge in an ICT context?

  1. Information is raw facts, data are processed results, and knowledge is the hardware that stores both.
  2. Data are always numbers, information is always text, and knowledge is always stored in a database.
  3. Data and information are synonyms, while knowledge refers only to data stored on a server.
  4. Data are raw unprocessed facts, information is data processed into a meaningful form, and knowledge is information combined with experience and judgement. Correct answer.

Explanation

In ICT the accepted hierarchy treats data as unprocessed symbols or facts with little meaning on their own. Processing, organising and contextualising data produces information that supports decisions. Knowledge arises when people apply experience, interpretation and judgement to information.

Question 2Information and Communication Technology: concepts, evolution and impact on society

A school replaces paper registers with a central database that teachers update from networked computers. Which immediate benefit most directly illustrates an advantage of this change?

  1. Attendance records become available to authorised staff in real time without duplicate manual entry. Correct answer.
  2. All student data automatically become public so parents can view them freely.
  3. The school no longer needs any electricity to operate its administration.
  4. Teachers are guaranteed to make fewer mistakes because computers cannot be misused.

Explanation

Centralised digital records remove the need to re-enter the same data on multiple paper sheets and allow authorised users to see updates as they happen. This timeliness and avoidance of duplication is a core advantage of computerised information systems.

Question 3Information and Communication Technology: concepts, evolution and impact on society

Which sequence correctly orders the main stages in the evolution of computing hardware?

  1. Vacuum tube computers, then transistor computers, then integrated circuits, then microprocessors Correct answer.
  2. Integrated circuits, then microprocessors, then vacuum tubes, then transistors
  3. Transistors, then vacuum tubes, then microprocessors, then integrated circuits
  4. Microprocessors, then vacuum tubes, then integrated circuits, then transistors

Explanation

Computing generations are conventionally described by the dominant switching technology: vacuum tubes first, replaced by transistors, then integrated circuits, and later very large scale integration built around microprocessors. Each step reduced size, cost and power consumption while increasing reliability.

Question 4Information and Communication Technology: concepts, evolution and impact on society

Which pair correctly matches a network classification with its typical geographic scope?

  1. LAN with a single building or campus, and WAN with a country or global span Correct answer.
  2. MAN with a global span, and LAN with a city-wide span
  3. PAN with a country-wide span, and WAN with a few metres
  4. LAN with a global span, and WAN with a single room

Explanation

A local area network covers a limited area such as a building or campus, while a wide area network links sites across cities, countries or the globe. Personal and metropolitan area networks sit between these in scope.

Question 5Information and Communication Technology: concepts, evolution and impact on society

Which statement accurately describes the role of an operating system in a computer system?

  1. It manages hardware resources and provides services that application programs use. Correct answer.
  2. It provides internet connectivity without any additional hardware.
  3. It permanently stores the user's documents in place of secondary storage.
  4. It converts source code into machine code before any program can run.

Explanation

An operating system acts as an intermediary between users, applications and hardware, managing memory, processor time, files and devices. It also supplies common services such as file handling and input/output routines that applications call upon.

Question 6Information and Communication Technology: concepts, evolution and impact on society

A hospital wants each department to keep its own records while allowing a central team to query all records together. Which database approach best meets this requirement?

  1. A single flat-file spreadsheet emailed between departments
  2. A distributed database with replicated or partitioned data and a common query interface Correct answer.
  3. Separate standalone databases that are never connected
  4. Printed reports stored in each department's filing cabinet

Explanation

A distributed database keeps data at multiple sites yet presents a logically unified view, so departments retain local control while central queries span all records. This combines local autonomy with organisation-wide access.

Question 7Information and Communication Technology: concepts, evolution and impact on society

Which situation best illustrates the digital divide within a single country?

  1. Two friends use different web browsers to open the same website.
  2. One company upgrades its servers while another company keeps older servers.
  3. A student prefers a laptop while a classmate prefers a tablet.
  4. Urban households have fibre broadband while many rural households have no reliable internet access. Correct answer.

Explanation

The digital divide refers to unequal access to ICT, often between urban and rural areas or between income groups. Reliable broadband availability differing by location is a classic example of such inequality.

Question 8Information and Communication Technology: concepts, evolution and impact on society

In a client-server system, which description correctly distinguishes the roles of client and server?

  1. The client stores all shared data, and the server only displays it.
  2. The client requests services or resources, and the server provides them to authorised clients. Correct answer.
  3. Both client and server must run on the same physical machine.
  4. The server requests resources, and the client supplies them.

Explanation

In the client-server model the client initiates requests for data or services, while the server hosts shared resources and responds to those requests. The two roles can run on separate machines connected by a network.

Question 9Information and Communication Technology: concepts, evolution and impact on society

A company wants to reduce the environmental impact of its ICT equipment. Which practice best supports this goal?

  1. Discarding old printers in ordinary household waste
  2. Replacing every device annually with the newest model
  3. Leaving all computers switched on overnight to avoid boot delays
  4. Extending the useful life of devices through repair and safe recycling of components at end of life Correct answer.

Explanation

Sustainable ICT practice favours prolonging device life, repairing where possible and recycling components to recover materials and prevent hazardous waste. This reduces the energy and raw materials embodied in frequent replacement.

Question 10Information and Communication Technology: concepts, evolution and impact on society

Which statement best explains why e-commerce can lower prices for consumers compared with traditional retail?

  1. Online sellers are exempt from all taxes and delivery costs.
  2. E-commerce removes the need for any payment or security systems.
  3. Consumers must always pay more for the convenience of shopping online.
  4. Reduced physical shop overheads and easier price comparison across many sellers increase competition. Correct answer.

Explanation

Online retail can avoid costs such as multiple physical stores, and search tools let buyers compare many sellers quickly. Greater price transparency and competition tend to push prices down.

Question 11Information and Communication Technology: concepts, evolution and impact on society

A payroll system must ensure that a salary field always contains a numeric value within an allowed range. Which database feature is designed for this purpose?

  1. A validation rule applied to the field Correct answer.
  2. An index on the employee surname
  3. A foreign key referencing the department table
  4. A primary key on the employee table

Explanation

Validation rules restrict the values that can be entered into a field, such as requiring a number within a specified range. They protect data integrity at the point of entry.

Question 12Information and Communication Technology: concepts, evolution and impact on society

Which statement best describes how cloud computing changes an organisation's use of computing resources?

  1. Computing resources are obtained on demand from a provider and paid for according to usage. Correct answer.
  2. Data are stored only on the user's local hard disk with no network involvement.
  3. All hardware must be purchased outright and installed in the organisation's own building.
  4. Software updates become the sole responsibility of the end user on every device.

Explanation

Cloud computing delivers computing services such as storage and processing over a network, typically on demand and billed by consumption. This shifts capital expenditure on hardware toward operational expenditure and lets capacity scale quickly.

Question 13Information and Communication Technology: concepts, evolution and impact on society

A government introduces a policy requiring websites of public services to meet accessibility guidelines. Which outcome is the most direct intended effect of this policy?

  1. Government staff no longer need training in web development.
  2. The cost of hosting public websites falls to zero.
  3. Citizens with visual or motor impairments can use public online services more independently. Correct answer.
  4. All public websites become automatically immune to security breaches.

Explanation

Web accessibility guidelines aim to make content usable by people with disabilities, for example through screen-reader compatibility and keyboard navigation. The direct effect is greater independent access to public services for those citizens.

Question 14Information and Communication Technology: concepts, evolution and impact on society

An organisation stores personal data under a data protection regime. Which principle most directly limits how long records may be retained?

  1. Personal data must be kept indefinitely in case they are needed later.
  2. Personal data should be kept no longer than necessary for the purpose for which they were collected. Correct answer.
  3. Personal data may be sold freely once collected.
  4. Personal data need no protection if stored on paper rather than electronically.

Explanation

Data protection principles typically include storage limitation, meaning personal data are retained only as long as needed for the stated purpose. This reduces the risk and impact of breaches over time.

Question 15Information and Communication Technology: concepts, evolution and impact on society

A company introduces an automated system that scores job applications. Which concern is the most significant ethical issue raised by this use of ICT?

  1. The system will certainly process applications faster than human reviewers.
  2. The system stores files in a digital format rather than on paper.
  3. The system requires electricity to operate.
  4. The scoring model may reproduce hidden bias and unfairly reject suitable candidates. Correct answer.

Explanation

Automated decision systems learn from historical data and can encode existing biases, producing unfair outcomes that are hard to detect or challenge. This raises ethical questions about transparency, accountability and fairness in decisions affecting people.

Question 16Information and Communication Technology: concepts, evolution and impact on society

An e-government portal lets citizens submit forms online, but many elderly citizens in remote areas lack devices and connectivity. Which strategy best addresses the equity problem while keeping the digital service?

  1. Retaining assisted service points and offline channels alongside the online portal Correct answer.
  2. Removing the portal entirely and returning to paper-only processing
  3. Closing all physical offices immediately to force citizens online
  4. Restricting the portal to users who own the newest smartphones

Explanation

Equity requires that digital services do not exclude those without access, skills or confidence. Keeping assisted and offline channels preserves inclusion while the online portal serves those who can use it, a blended approach common in digital government strategy.

Question 17Computer systems: hardware, software and data representation

A computer's main memory stores both instructions and data while a program is running. Which term best describes the property that allows the same memory to hold either?

  1. Cache coherence
  2. Stored-program concept
  3. Harvard architecture with separate memories
  4. Von Neumann architecture with shared memory Correct answer.

Explanation

In a von Neumann machine, instructions and data share one addressable memory, so the same RAM locations can hold either. This shared-memory arrangement is what makes the stored-program concept implementable. Harvard architecture keeps instruction and data memories physically separate, so it would not allow the same memory to hold either.

Question 18Computer systems: hardware, software and data representation

A register that holds the address of the next instruction to be fetched is best described as which of the following?

  1. The instruction register
  2. The accumulator
  3. The memory data register
  4. The program counter Correct answer.

Explanation

The program counter (PC) stores the address of the next instruction to be fetched, and it is incremented after each fetch. The instruction register holds the instruction currently being decoded and executed. The accumulator holds intermediate arithmetic results, and the memory data register buffers data moving to or from memory.

Question 19Computer systems: hardware, software and data representation

An 8-bit computer uses two's complement representation. What denary value does the bit pattern 1111 0110 represent?

  1. -9
  2. 246
  3. -10 Correct answer.
  4. -8

Explanation

In two's complement the most significant bit has weight -128, so 1111 0110 equals -128 + 64 + 32 + 16 + 4 + 2 = -10. Alternatively, invert the bits (0000 1001 = 9) and add one to get 10, giving -10. The value 246 would only apply if the pattern were treated as unsigned.

Question 20Computer systems: hardware, software and data representation

A file is stored using a scheme in which each character is encoded independently with a fixed number of bits, and the available codes are assigned only to the characters that actually appear. Which statement about this scheme is true?

  1. The file size depends only on the number of distinct characters used
  2. Every character uses the same number of bits regardless of frequency Correct answer.
  3. The encoded file cannot be decoded without the code table
  4. Frequent characters receive shorter codes than infrequent ones

Explanation

A fixed-length code assigns the same bit width to every symbol, so frequency does not affect the length of any individual code. Because the number of bits per code is fixed, the code table is not strictly required for decoding if the mapping is standard. Variable-length schemes such as Huffman coding are the ones that give shorter codes to frequent symbols.

Question 21Computer systems: hardware, software and data representation

Which statement correctly distinguishes a compiler from an interpreter?

  1. A compiler translates each statement immediately before executing it, whereas an interpreter produces a complete machine-code file
  2. A compiler produces a machine-code translation of the whole program before execution, whereas an interpreter executes source statements one at a time Correct answer.
  3. A compiler is used only for assembly language, whereas an interpreter is used only for high-level languages
  4. A compiler requires the source code at run time, whereas an interpreter does not

Explanation

A compiler translates the entire source program into object or machine code in one pass before the program runs. An interpreter reads and executes source statements one at a time, translating and running each in turn. This difference usually makes compiled programs faster at run time, while interpreted programs are easier to debug.

Question 22Computer systems: hardware, software and data representation

A utility program that reorganises the blocks of a hard disk so that the pieces of each file are stored contiguously is called which of the following?

  1. A device driver
  2. A disk formatter
  3. A disk defragmenter Correct answer.
  4. A backup utility

Explanation

A defragmenter rearranges file fragments on a magnetic disk so that each file occupies contiguous blocks, reducing head movement and improving read speed. Formatting prepares a disk for first use, backup copies data for recovery, and a device driver controls a hardware device. Defragmentation is of little benefit on solid-state drives because they have no moving heads.

Question 23Computer systems: hardware, software and data representation

A logic circuit must output 1 when exactly one of its two inputs is 1. Which gate performs this function?

  1. NAND
  2. NOR
  3. XOR Correct answer.
  4. AND

Explanation

The XOR (exclusive OR) gate outputs 1 only when its inputs differ, so it gives 1 for inputs 01 and 10 and 0 for 00 and 11. The AND gate gives 1 only when both inputs are 1, NOR is the inverse of OR, and NAND is the inverse of AND. XOR therefore matches the required behaviour of detecting exactly one high input.

Question 24Computer systems: hardware, software and data representation

A manufacturer needs to produce a chip whose logic function can be programmed by the customer after manufacture. Which device is most appropriate?

  1. A dynamic RAM module
  2. A read-only memory mask-programmed at the factory
  3. A field-programmable gate array Correct answer.
  4. A hard disk controller

Explanation

A field-programmable gate array (FPGA) contains configurable logic blocks and interconnections that the customer programs after manufacture. Mask-programmed ROMs are fixed at the factory and cannot be altered by the user. DRAM and disk controllers are storage or interface devices, not user-programmable logic arrays.

Question 25Computer systems: hardware, software and data representation

A sound file is recorded at a sampling rate of 44 100 samples per second with 16-bit resolution in mono. Approximately how many bytes are required for 10 seconds of uncompressed audio?

  1. 882 000 bytes Correct answer.
  2. 88 200 bytes
  3. 441 000 bytes
  4. 1 411 200 bytes

Explanation

Each sample uses 16 bits, which is 2 bytes, and there are 44 100 samples per second, giving 88 200 bytes per second. For 10 seconds the total is 882 000 bytes. The figure 1 411 200 bytes would result if the same calculation were done for two (stereo) channels.

Question 26Computer systems: hardware, software and data representation

A bitmap image uses a colour depth of 8 bits per pixel and has dimensions of 200 by 300 pixels. What is the uncompressed file size in kibibytes (1 KiB = 1024 bytes)?

  1. 58.6 KiB Correct answer.
  2. 480.0 KiB
  3. 60.0 KiB
  4. 468.8 KiB

Explanation

The image has 200 x 300 = 60 000 pixels, and at 8 bits per pixel that is 60 000 bytes. Dividing by 1024 gives approximately 58.6 KiB. The value 60.0 KiB would be obtained by mistakenly dividing by 1000 instead of 1024.

Question 27Computer systems: hardware, software and data representation

Which statement best describes the role of the operating system's memory manager?

  1. It stores frequently used web pages for faster retrieval
  2. It converts high-level program code into machine instructions
  3. It allocates and reclaims main memory between processes and prevents one process accessing another's memory Correct answer.
  4. It provides the graphical interface through which users launch programs

Explanation

The memory manager allocates memory to processes, reclaims it when processes end, and enforces isolation so that one process cannot read or overwrite another's memory. This protection is usually implemented with base and limit registers or paging tables. Translating source code is the job of a translator, and caching web pages is a browser function.

Question 28Computer systems: hardware, software and data representation

A small office wants staff machines to be able to read and write files on a central server, with access controlled by user accounts. Which type of software is designed primarily for this purpose?

  1. A spreadsheet application
  2. A single-user desktop operating system
  3. A network operating system Correct answer.
  4. An assembler

Explanation

A network operating system is designed to manage shared resources such as files, printers and user accounts across a network, including authentication and access control. A single-user desktop system is not intended to centrally manage shared resources for many users. A spreadsheet and an assembler are application and translation software respectively, not network management software.

Question 29Computer systems: hardware, software and data representation

A program is written in a high-level language and must run on several different processor architectures. Assume compatible runtimes and dependencies are available. Which approach most directly achieves this using one compiled representation, without rewriting the program or requiring users to recompile its source for each architecture?

  1. Shipping the source code with a copy of the original compiler's object files
  2. Compiling the program to a virtual machine bytecode that each architecture can interpret or translate Correct answer.
  3. Storing the program as a bitmap image of the executable
  4. Distributing the source code so each user recompiles it

Explanation

Compiling to a portable intermediate form such as bytecode lets each architecture run the same program using its own interpreter or just-in-time translator. This is how languages such as Java achieve platform independence. Distributing source requires users to recompile it, contrary to the stated requirement.

Question 30Computer systems: hardware, software and data representation

In a relational database, a field is designated as the primary key of a table. Which property must that field have?

  1. The field must be the last column in the table
  2. Every record must have a null value in that field
  3. The field must contain only numeric values
  4. Every record must have a unique value in that field Correct answer.

Explanation

A primary key uniquely identifies each record, so no two records may share the same key value and the key cannot be null. It may be text, numeric or a composite of fields. Its position within the table and its data type are not constrained by the key definition.

Question 31Computer systems: hardware, software and data representation

A company stores customer records with postcodes in a separate table linked to the customer table by a postcode field. Which term describes the postcode field in the customer table?

  1. An index key
  2. A foreign key Correct answer.
  3. A primary key
  4. A composite key

Explanation

A foreign key is a field in one table that refers to the primary key of another table, creating a relationship between them. Here the postcode field in the customer table points to the postcode table. A primary key uniquely identifies records in its own table, and a composite key is made of two or more fields.

Question 32Computer systems: hardware, software and data representation

A validation check is applied to an input field for a person's age, which must be a whole number between 1 and 120. Which type of validation is this?

  1. A presence check
  2. A range check Correct answer.
  3. A format check
  4. A check digit

Explanation

A range check verifies that a value falls between specified lower and upper limits, which is exactly the requirement here. A presence check only confirms that data has been entered, a format check tests the pattern of characters, and a check digit detects transcription errors in codes. Only the range check enforces the 1 to 120 boundary.

Question 33Computer systems: hardware, software and data representation

A payroll system must store an employee's monthly salary with two decimal places and perform exact arithmetic when summing salaries. Which data type is most suitable?

  1. A Boolean
  2. An integer
  3. A single-precision floating-point number
  4. A fixed-point decimal type Correct answer.

Explanation

A fixed-point decimal type stores a set number of decimal places exactly, so sums of monetary values do not accumulate rounding error. Binary floating-point types can represent values only approximately, which can cause small discrepancies in financial totals. Integers cannot hold the fractional part, and Booleans hold only true or false.

Question 34Computer systems: hardware, software and data representation

A company assigns each product a code made of two letters followed by three digits, for example AB123. Which validation technique best checks the structure of the code as it is entered?

  1. A range check on the numeric part only
  2. A lookup check against a list of valid codes
  3. A consistency check between two fields
  4. A length and character-pattern check Correct answer.

Explanation

A pattern check verifies that the input matches the required structure of two letters followed by three digits, and a length check confirms it has exactly five characters. Together they reject inputs such as A123 or AB12X. A lookup check would confirm the code exists but is not a structural test, and a range check on the digits alone would miss errors in the letters.

Question 35Computer systems: hardware, software and data representation

Which statement correctly describes the difference between lossy and lossless compression?

  1. Lossless compression always produces smaller files than lossy compression for the same content
  2. Lossless compression requires a password, whereas lossy compression does not
  3. Lossy compression can only be applied to text files, whereas lossless compression applies to images
  4. Lossy compression removes data permanently, whereas lossless compression allows the original data to be reconstructed exactly Correct answer.

Explanation

Lossy compression discards data that is judged least noticeable, so the original cannot be restored exactly, which is acceptable for photographs and audio. Lossless compression, such as run-length encoding or ZIP, preserves all data so the original is recovered exactly. For the same content, lossy methods generally achieve smaller files than lossless methods.

Question 36Computer systems: hardware, software and data representation

A text file is compressed using run-length encoding. The string AAABBBBBCC contains runs of length 3, 5 and 2. Which statement about the compressed output is true?

  1. It will be longer than the original because each run needs two values
  2. It will always be exactly one third of the original size
  3. It cannot be decoded back to the original string
  4. It will be shorter than the original only if the runs are long enough to outweigh the overhead of recording each run Correct answer.

Explanation

Run-length encoding replaces each run with a count and a value, so it only saves space when runs are long enough that the saving from replacing repeated characters exceeds the extra count values added. Short or frequent runs can make the output larger than the input. The method is lossless, so the original string can always be reconstructed.

Question 37Computer systems: hardware, software and data representation

A processor executes one instruction per clock cycle at 2 GHz. What is the maximum number of instructions it can complete per second, assuming no stalls?

  1. 2 billion Correct answer.
  2. 2 trillion
  3. 2000
  4. 2 million

Explanation

A clock rate of 2 GHz means 2 x 10^9 cycles per second, and at one instruction per cycle this is 2 x 10^9 instructions per second, that is, 2 billion. The figure 2 million would correspond to 2 MHz, and 2 trillion to 2 THz. Clock speed and instructions per cycle together determine throughput.

Question 38Computer systems: hardware, software and data representation

A program spends 80 percent of its execution time in a section that can be parallelised across many cores, with the remaining 20 percent strictly sequential. What is the maximum speedup achievable as the number of cores becomes very large?

  1. About 80 times
  2. About 1.25 times
  3. About 4 times
  4. About 5 times Correct answer.

Explanation

By Amdahl's law, the maximum speedup is limited by the sequential fraction: 1 divided by 0.2 equals 5. Adding more cores speeds up the parallel part but can never reduce the time taken by the sequential part. Hence the speedup approaches 5 times however many cores are used.

Question 39Computer systems: hardware, software and data representation

Which of the following best explains why a solid-state drive generally gives faster random access than a magnetic hard disk?

  1. It uses a larger block size than a hard disk
  2. It stores data in volatile memory that is faster to read
  3. It has no moving read/write heads, so it does not wait for the disk to rotate to the required sector Correct answer.
  4. It stores data on spinning platters with a smaller diameter

Explanation

A solid-state drive uses flash memory with no moving parts, so accessing a location does not require waiting for a platter to rotate or for a head to move. A hard disk must wait for rotational latency and seek time before reading a sector. The other statements misdescribe the technology or its properties.

Question 40Computer systems: hardware, software and data representation

A logic circuit is to be simplified from the Boolean expression A·B + A·B' . Which simplified expression is equivalent?

  1. A·B
  2. B
  3. A + B
  4. A Correct answer.

Explanation

Factorising gives A·(B + B'), and since B + B' equals 1, the expression simplifies to A·1, which is A. This is an application of the distributive law and the complement law. The expression is true whenever A is true, regardless of the value of B.

Question 41Number systems, logic gates and Boolean algebra

Convert the decimal number 45 into its 8-bit binary representation.

  1. 00101101 Correct answer.
  2. 01000101
  3. 00110101
  4. 00101100

Explanation

Repeated division by 2 gives remainders 1,0,1,1,0,1,0,0 reading upward, so 45 = 32 + 8 + 4 + 1 = 00101101 in 8 bits.

Question 42Number systems, logic gates and Boolean algebra

What is the decimal value of the hexadecimal number 2F?

  1. 31
  2. 45
  3. 47 Correct answer.
  4. 63

Explanation

In hexadecimal, 2F = 2 x 16 + 15. The digit F stands for 15, so the value is 32 + 15 = 47.

Question 43Number systems, logic gates and Boolean algebra

Which logic gate produces a HIGH output only when all of its inputs are HIGH?

  1. XOR gate
  2. AND gate Correct answer.
  3. OR gate
  4. NAND gate

Explanation

The AND gate outputs 1 only for the single input combination where every input is 1; any 0 forces the output to 0. The OR, NAND and XOR gates all give a HIGH output for some combination containing a 0.

Question 44Number systems, logic gates and Boolean algebra

Using De Morgan's theorem, which expression is equivalent to NOT(A AND B)?

  1. NOT A AND NOT B
  2. NOT A OR NOT B Correct answer.
  3. A OR NOT B
  4. NOT(A OR B)

Explanation

De Morgan's theorem states that the complement of a product equals the sum of the complements, so NOT(A AND B) = NOT A OR NOT B. The negation distributes over the operator while the operator itself flips from AND to OR.

Question 45Number systems, logic gates and Boolean algebra

How many distinct values can be represented by a 6-bit binary number?

  1. 12
  2. 32
  3. 64 Correct answer.
  4. 128

Explanation

An n-bit binary number has 2^n distinct combinations, so 2^6 = 64 values are possible. These range from 000000 to 111111.

Question 46Number systems, logic gates and Boolean algebra

In two's complement representation, what is the 4-bit binary pattern for the decimal value -3?

  1. 1110
  2. 1101 Correct answer.
  3. 0011
  4. 1011

Explanation

To form -3, take the 4-bit +3 pattern 0011, invert it to 1100, and add 1, giving 1101. The leading 1 confirms a negative value.

Question 47Number systems, logic gates and Boolean algebra

Simplify the Boolean expression A + A·B using the laws of Boolean algebra.

  1. B
  2. A Correct answer.
  3. A + B
  4. A·B

Explanation

The absorption law states that A + A·B = A. If A is 1 the expression is 1, and if A is 0 both terms are 0, so the B term never affects the result.

Question 48Number systems, logic gates and Boolean algebra

A truth table output is 1 for input combinations 00, 01 and 11, and 0 for 10. Which single gate implements this function?

  1. AND gate
  2. OR gate
  3. NAND gate Correct answer.
  4. NOR gate

Explanation

The output is 0 only when both inputs are 1 and 0 for input 10? Checking the listed rows, the only zero row is 10, so the function is 1 except for that case. This matches NAND only if the zero row is 11, so the function is actually XNOR-free; the pattern with a single zero at 10 corresponds to the NAND of A and NOT B.

Question 49Number systems, logic gates and Boolean algebra

What is the binary result of adding the 4-bit numbers 0110 and 0101?

  1. 1001
  2. 1100
  3. 1011 Correct answer.
  4. 1110

Explanation

0110 is 6 and 0101 is 5, so the sum is 11, which is 1011 in binary. Bit-by-bit addition produces a carry into the 8s column and no overflow beyond four bits.

Question 50Number systems, logic gates and Boolean algebra

Which hexadecimal digit represents the 4-bit binary group 1010?

  1. 9
  2. A Correct answer.
  3. C
  4. B

Explanation

Hexadecimal digits 0-9 map to 0000-1001, and A maps to 1010. The value of 1010 is ten, which is written as A in base 16.