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IB Digital Society SL practice questions

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Question 1Digital systems

In a digital system, a single byte is made up of eight bits. How many distinct bit patterns can one byte hold?

  1. 128
  2. 512
  3. 64
  4. 256 Correct answer.

Explanation

Each additional bit doubles the number of possible patterns, so eight bits give 2^8 = 256 patterns, running from 00000000 to 11111111. This follows from binary positional representation and does not depend on what the byte is used to store.

Question 2Digital systems

A washing machine contains a microcontroller running a fixed control loop for its wash cycle, with no facility for users to install other software. Which term best describes this microcontroller?

  1. A virtual machine
  2. A distributed database
  3. A general-purpose desktop processor
  4. An embedded system Correct answer.

Explanation

An embedded system combines hardware and software dedicated to a specific function inside a larger device, often with real-time constraints and limited memory or processing power. Because it runs a fixed control program rather than arbitrary user applications, it is not a general-purpose computer.

Question 3Digital systems

In a peer-to-peer file-sharing network, which statement describes how data is exchanged?

  1. A single central server stores and distributes every file to all clients.
  2. Clients request files only from an authoritative database administrator.
  3. All nodes share one virtual machine image hosted in a public cloud.
  4. Each node can both request files and serve them to other nodes. Correct answer.

Explanation

In a peer-to-peer architecture each participating device can act as both client and server, requesting content while also supplying it to others. This removes the need for a central server to carry all the file traffic, although a separate service may still help nodes discover each other.

Question 4Digital systems

What is the primary function of a hypervisor in a virtualised digital system?

  1. It allocates physical hardware resources among multiple guest operating systems. Correct answer.
  2. It converts analogue sensor signals into digital values.
  3. It compiles source code into machine code for the host processor.
  4. It encrypts traffic travelling between the host and the internet.

Explanation

A hypervisor creates and runs virtual machines, mediating access to the physical CPU, memory and input/output devices so several guest operating systems can share one host. A type 1 hypervisor runs directly on the hardware, while a type 2 hypervisor runs on top of a host operating system.

Question 5Digital systems

A school rents virtual machines and storage from a cloud provider, then installs and patches its own operating system and applications on them. Which cloud service model is this?

  1. Infrastructure as a Service (IaaS) Correct answer.
  2. Function as a Service (FaaS)
  3. Platform as a Service (PaaS)
  4. Software as a Service (SaaS)

Explanation

IaaS supplies raw compute, storage and networking resources, leaving the customer responsible for the operating system, middleware and applications above that layer. The school's need to patch its own operating system is the detail that distinguishes this from managed platform or software offerings.

Question 6Digital systems

A computer with limited RAM runs several large applications at once. Which operating-system technique lets each process use more memory than is physically installed?

  1. Virtual memory with paging Correct answer.
  2. Interrupt polling
  3. Instruction pipelining
  4. Disk defragmentation

Explanation

Virtual memory gives each process its own address space and maps virtual addresses to physical frames, moving pages that are not currently needed out to secondary storage. When a required page is absent from RAM, a page fault brings it back, so the total apparent memory can exceed the installed RAM.

Question 7Digital systems

A live video call can tolerate occasional lost frames but needs very low delay. Which transport protocol behaviour best suits this requirement?

  1. TCP, because it encrypts all packets by default
  2. UDP, because it guarantees ordered delivery of all packets
  3. UDP, because it avoids retransmission and connection setup delays Correct answer.
  4. TCP, because it retransmits every lost segment before delivering later data

Explanation

UDP is connectionless: it does not guarantee delivery or ordering and does not retransmit lost datagrams, so a late frame is simply discarded rather than delaying later ones. Real-time media therefore usually prefers UDP, accepting minor loss in exchange for lower latency, while TCP's reliability mechanisms can cause head-of-line delays.

Question 8Digital systems

A weather app displays forecasts by calling a remote service that returns JSON data. What is the main role of the API in this system?

  1. It defines a request interface that hides the service's internal implementation. Correct answer.
  2. It compiles the app's source code for the mobile processor.
  3. It stores a copy of the forecast on the phone's local storage.
  4. It physically hosts the remote servers that compute and store the forecast data.

Explanation

An API is a defined contract specifying which requests a client may make, what format the responses take and which errors can occur. It lets the app obtain data without knowing how the service stores or computes it, so the provider can change its internals without breaking the app.

Question 9Digital systems

An environmental sensor outputs a continuously changing voltage. A microcontroller records the voltage every 100 ms and stores each reading as an 8-bit value. Which pair of processes does the system perform?

  1. Digital-to-analogue conversion and sampling at 10 Hz
  2. Digital-to-analogue conversion and sampling at 100 Hz
  3. Analogue-to-digital conversion and sampling at 100 Hz
  4. Analogue-to-digital conversion and sampling at 10 Hz Correct answer.

Explanation

Replacing a continuously varying voltage with discrete numeric values is analogue-to-digital conversion, which includes quantising each reading into a fixed number of bits. Readings taken every 100 ms occur ten times per second, so the sampling rate is 10 Hz.

Question 10Digital systems

A system's CPU is idle about 70% of the time while waiting for disk reads, and the disk is busy almost constantly. Which change is most likely to improve overall throughput?

  1. Increasing the memory installed in the office printer
  2. Upgrading the CPU to a model with a higher clock speed
  3. Moving frequently read data to a faster cache or SSD Correct answer.
  4. Increasing the bandwidth of the server's internet connection

Explanation

Throughput is limited by the slowest component, so when the CPU is mostly idle waiting on storage the disk is the bottleneck. Reducing storage latency through caching or a faster device attacks that constraint directly, whereas speeding up an already idle resource leaves overall throughput largely unchanged.

Question 11Digital systems

A digital circuit uses a two-input AND gate. What is the output when input A is 1 and input B is 0?

  1. 0 Correct answer.
  2. 1
  3. High impedance
  4. Undefined

Explanation

An AND gate outputs 1 only when every input is 1. With A=1 and B=0, that condition is not met, so the output is 0. A standard logic gate produces a defined logic level for valid logic inputs.

Question 12Digital systems

During the fetch–decode–execute cycle, what happens immediately after an instruction is fetched from memory?

  1. It is decoded. Correct answer.
  2. It is sent to the printer.
  3. It is permanently stored in ROM.
  4. It is written to secondary storage.

Explanation

The cycle first retrieves the instruction from memory, then decodes it to identify the operation and operands. Execution follows decoding, and any result storage happens later. The fetched instruction is not written to secondary storage or ROM during this step.

Question 13Digital systems

A photographer needs to reduce image file sizes for a website but must be able to restore every original pixel value exactly. Which approach meets this requirement?

  1. Lossless compression, which preserves all original data Correct answer.
  2. No compression, because compression always changes pixel values
  3. Lossy compression, because it discards detail the eye cannot see
  4. Encryption, because it reduces file size while protecting the image

Explanation

Lossless compression encodes data so that decompression restores the exact original bit pattern, including every pixel value. Lossy compression permanently discards some information and therefore changes pixel values. Encryption protects confidentiality but does not normally reduce file size.

Question 14Digital systems

A CPU repeatedly accesses the same small set of instructions. Which component is designed to reduce average access time by holding recently used instructions close to the processor?

  1. The RAM module
  2. The cache memory Correct answer.
  3. The hard disk controller
  4. The arithmetic logic unit

Explanation

Cache is a small, fast memory close to the CPU that holds recently or frequently used instructions and data. It reduces average memory access time compared with fetching from RAM. The ALU performs arithmetic and logic operations, while disk controllers manage secondary storage.

Question 15Digital systems

A user types a domain name into a browser. Which system translates that human-readable name into an IP address?

  1. NAT
  2. DHCP
  3. DNS Correct answer.
  4. HTTP

Explanation

The Domain Name System resolves human-readable domain names into IP addresses so clients can reach the correct server. DHCP assigns network configuration, NAT translates private and public addresses, and HTTP transfers web content.

Question 16Digital systems

A server stores its data on a RAID 1 array with two disks. If one disk fails, what remains true?

  1. The failed disk is rebuilt from parity on the remaining disk.
  2. The data remains available from the mirrored disk. Correct answer.
  3. All data on the array is lost until the failed disk is replaced.
  4. The array continues with doubled storage capacity.

Explanation

RAID 1 mirrors identical data across two disks, so either disk can serve the data if the other fails. There is no parity reconstruction in RAID 1, and a single disk failure does not destroy the data. Usable capacity is half the raw capacity, not doubled.

Question 17Digital systems

A website uses HTTPS. Which key does the browser use to encrypt the session key so that only the server can decrypt it?

  1. The browser's private key
  2. A shared password sent in plain text
  3. The server's public key Correct answer.
  4. The server's private key

Explanation

In TLS, the browser encrypts a session key with the server's public key, and only the matching server private key can decrypt it. The session key then protects the connection. The browser's private key is not shared with the server, and a plain-text password would not provide confidentiality.

Question 18Digital systems

A company adopts software released under an open-source licence. Which characteristic is granted by such a licence?

  1. The software must be free of charge.
  2. The software cannot contain security vulnerabilities.
  3. The original developer must provide 24-hour support.
  4. The source code can be inspected and modified. Correct answer.

Explanation

An open-source licence grants permission to inspect, modify, and redistribute source code, subject to conditions such as attribution or copyleft. It does not guarantee zero cost, absence of bugs, or vendor support. These matters depend on the specific licence and on separate service agreements.

Question 19Digital systems

A network uses the subnet mask 255.255.255.192. How many usable host addresses does each subnet provide?

  1. 126
  2. 30
  3. 64
  4. 62 Correct answer.

Explanation

A /26 subnet mask leaves 6 host bits because 32 − 26 = 6. That gives 2^6 = 64 total addresses, and subtracting the network and broadcast addresses leaves 62 usable host addresses.

Question 20Digital systems

A banking system transfers money between two accounts. Which transaction property ensures that the debit and the credit are both applied or neither is applied?

  1. Atomicity Correct answer.
  2. Consistency
  3. Isolation
  4. Durability

Explanation

Atomicity guarantees that a transaction is treated as a single unit: either all its operations commit or none do. In a transfer, a debit without a matching credit would violate atomicity. Durability concerns persistence after commit, isolation concerns concurrent transactions, and consistency concerns valid state transitions.

Question 21Digital systems

A digital circuit combines two sensor signals with an XOR gate. If input A is 1 and input B is 1, what is the output?

  1. 0, because the inputs are both 1 Correct answer.
  2. 0, because both inputs are 0
  3. 1, because the inputs are both 1
  4. 1, because the inputs are different

Explanation

An XOR gate outputs 1 only when its two inputs differ. With A = 1 and B = 1 the inputs are the same, so the output is 0. This differs from an OR gate, which would output 1 for the same inputs.

Question 22Digital systems

A laptop specification lists a solid-state drive instead of a magnetic hard disk. Which property most directly explains why the SSD usually starts up faster?

  1. It reads data using a laser and optical pits.
  2. It compresses every stored file automatically.
  3. It keeps all data permanently in the CPU cache.
  4. It has no moving mechanical parts. Correct answer.

Explanation

An SSD stores data in flash memory and has no spinning platters or moving read/write heads. Avoiding mechanical movement makes random access and startup much faster than on a magnetic hard disk. Compression, CPU cache, and optical reading do not describe an SSD.

Question 23Digital systems

A home network connects a laptop, phone, and smart TV to the internet. Which device forwards packets between this local network and the internet based on IP addresses?

  1. A router Correct answer.
  2. A solid-state drive
  3. A USB hub
  4. An uninterruptible power supply

Explanation

A router forwards packets between networks and uses IP addresses to choose the next hop. A hub only repeats signals within a local segment and does not route between the home network and the internet. The other devices provide storage or power, not network routing.

Question 24Digital systems

An operating system must share one CPU among several interactive users so that no single process monopolises the processor. Which scheduling approach best matches this requirement?

  1. Suspending processes when a key is pressed
  2. First-come, first-served to completion
  3. Round-robin with fixed time slices Correct answer.
  4. Prioritising the process using most memory

Explanation

Round-robin scheduling gives each ready process a turn on the CPU for a fixed time slice. This prevents one interactive process from monopolising the processor and provides fair sharing. Running processes to completion or suspending all work for a key press would harm responsiveness.

Question 25Digital systems

A video call sends digitised voice as small packets across the internet. Which statement describes packet switching in this situation?

  1. A dedicated physical circuit stays open for the whole call.
  2. Packets may take different routes and are reassembled. Correct answer.
  3. The network sends the entire call as one continuous file.
  4. All packets follow one fixed route and arrive in order.

Explanation

Packet switching breaks data into packets that can travel independently over shared networks. Packets may follow different routes and are reassembled in the correct order at the destination. A dedicated circuit and one continuous file describe circuit switching or file transfer, not packet switching.

Question 26Digital systems

A development team wants to deploy code without installing or patching the underlying operating system or runtime. Which cloud service model provides this managed environment?

  1. Software as a Service (SaaS)
  2. Platform as a Service (PaaS) Correct answer.
  3. Infrastructure as a Service (IaaS)
  4. Desktop as a Service (DaaS)

Explanation

PaaS supplies a managed platform, including the runtime and operating system, so developers can deploy code without patching servers themselves. IaaS would require the team to manage the operating system, and SaaS provides finished applications rather than a deployment platform.

Question 27Digital systems

A download page publishes a SHA-256 hash next to a software installer. A user computes the hash of the downloaded file and compares it with the published value. What does a match primarily confirm?

  1. The file is free of all malware.
  2. The file has not changed since the hash was published. Correct answer.
  3. The file was downloaded from an official server.
  4. The file will run on every operating system.

Explanation

A cryptographic hash acts as a fingerprint of the file contents. If the computed hash matches the published value, the file has not changed since that hash was created. Hashing alone does not prove the server was official, guarantee malware freedom, or show operating-system compatibility.

Question 28Digital systems

While a computer is running a spreadsheet calculation, a printer signals that it has finished a print job. Which mechanism allows the processor to respond without constantly checking the printer?

  1. Direct memory access ignoring the CPU
  2. A cold reboot of the system
  3. An interrupt request sent to the CPU Correct answer.
  4. A page fault in virtual memory

Explanation

An interrupt is a signal that tells the CPU to pause its current work and handle an event, such as a printer completing a job. This avoids wasteful polling in which the processor repeatedly checks the device. Direct memory access, rebooting, and page faults serve different purposes.

Question 29Digital systems

An 8-bit signed integer is stored using two's complement. Which range of decimal values can it represent?

  1. 0 to 255
  2. -127 to +127
  3. -128 to +127 Correct answer.
  4. -255 to +255

Explanation

In 8-bit two's complement, one pattern represents zero, 127 patterns represent positive values, and 128 patterns represent negative values. The range is therefore -128 to +127. Unsigned 8-bit values instead span 0 to 255.

Question 30Digital systems

Computer A has a higher clock speed than Computer B, yet Computer B completes a video-rendering task faster. Which explanation is most plausible?

  1. Computer A must have a larger hard disk.
  2. Computer B has a lower-resolution monitor.
  3. Clock speed alone always determines processing speed.
  4. Computer B does more work per clock cycle. Correct answer.

Explanation

Clock speed is only one factor in performance; instructions per cycle, core count, cache, and memory speed also matter. A lower-clocked CPU can finish faster if it does more useful work per cycle or exploits parallelism better. Disk size and monitor resolution do not determine rendering speed in this way.

Question 31Digital systems

A school wants students to use email and document editing through a web browser while the provider maintains all servers, runtimes, and updates. Which cloud service model delivers this complete application experience?

  1. Software as a Service (SaaS) Correct answer.
  2. Platform as a Service (PaaS)
  3. Infrastructure as a Service (IaaS)
  4. Function as a Service (FaaS)

Explanation

SaaS provides fully managed applications over the internet, so users access software through a browser while the provider handles servers, runtime, storage, and updates. IaaS supplies virtualised infrastructure, PaaS supplies a deployment platform, and FaaS runs event-triggered functions rather than complete office applications.

Question 32Digital systems

A smart greenhouse uses soil-moisture sensors connected to a controller. When moisture falls below a threshold, the controller sends a signal that opens a water valve. Which term describes the valve in this system?

  1. Actuator Correct answer.
  2. Sensor
  3. Microcontroller
  4. Gateway

Explanation

An actuator converts a control signal into a physical action, such as opening or closing a valve. Sensors measure conditions, gateways connect networks, and microcontrollers process logic and issue control signals.

Question 33Digital systems

A washing machine contains a dedicated processor running fixed firmware to control its motor, water valves, and display. Which term best describes this processor within the washing machine?

  1. Graphics processing unit
  2. Embedded system Correct answer.
  3. General-purpose CPU
  4. Mainframe

Explanation

An embedded system is a dedicated computer built into a larger device to perform a specific control task, often with fixed firmware. General-purpose CPUs, mainframes, and GPUs are not defined by this dedicated, device-integrated role.

Question 34Digital systems

A file-sharing application lets each user's computer request files from and supply files to other users, with no central server storing the shared files. Which architecture does this describe?

  1. Star topology
  2. Thin-client
  3. Peer-to-peer Correct answer.
  4. Client–server

Explanation

In a peer-to-peer architecture each node can act as both client and server, so files are exchanged directly among users. Client–server relies on a central server, thin-client describes local devices depending on a server, and star topology describes a network layout.

Question 35Digital systems

A single physical server runs several isolated operating systems, each unaware of the others and each receiving a share of CPU, memory, and storage. Which component creates and allocates resources to these isolated operating systems?

  1. Compiler
  2. Bootloader
  3. Hypervisor Correct answer.
  4. Device driver

Explanation

A hypervisor, also called a virtual machine monitor, creates and runs virtual machines and allocates physical resources among them. A compiler translates code, a bootloader starts an operating system, and a device driver controls specific hardware.

Question 36Digital systems

An autonomous vehicle must brake within milliseconds, and sending sensor data to a distant cloud data centre would add delay. Which approach reduces latency by processing data close to the vehicle?

  1. Cloud bursting
  2. Batch processing
  3. Edge computing Correct answer.
  4. Grid computing

Explanation

Edge computing processes data near where it is generated, reducing the distance and delay before a response. Grid computing and cloud bursting distribute work across remote resources, while batch processing collects work into groups for later handling.

Question 37Digital systems

A system is trained on thousands of X-ray images that have already been marked by radiologists as either "fracture" or "no fracture". It then predicts a label for new images. Which type of machine learning is being used?

  1. Unsupervised learning
  2. Supervised learning Correct answer.
  3. Reinforcement learning
  4. Rule-based expert system

Explanation

Supervised learning trains a model on examples with known labels so that it can predict labels for new data. Unsupervised learning finds patterns without labels, reinforcement learning learns from rewards, and expert systems rely on hand-coded rules.

Question 38Digital systems

A weather app sends requests to a remote service using a documented set of endpoints and receives forecast data as JSON. The app does not access the service's database or internal code. Which term describes this documented interface?

  1. Integrated development environment (IDE)
  2. Software development kit (SDK)
  3. Application programming interface (API) Correct answer.
  4. Command-line interface (CLI)

Explanation

An API defines a contract that lets one program request services or data from another without exposing internal implementation details. An SDK bundles development tools, an IDE is a coding environment, and a CLI accepts typed commands from a user.

Question 39Digital systems

As data moves down the TCP/IP stack, each layer adds its own header so that the receiving layer can interpret the message correctly. What is this process called?

  1. Fragmentation
  2. Encapsulation Correct answer.
  3. Routing
  4. Multiplexing

Explanation

Encapsulation adds protocol headers, and sometimes trailers, as data passes down the layers so each layer can process its own information independently. Multiplexing shares a connection, routing chooses paths between networks, and fragmentation splits packets that are too large.

Question 40Digital systems

An online game responds slowly to player actions even though the same connection downloads large files quickly. Which network characteristic best explains the delayed responses?

  1. Latency Correct answer.
  2. Storage capacity
  3. Bandwidth
  4. Compression ratio

Explanation

Latency is the delay between sending a request and receiving a response, so high latency causes lag even when bandwidth is high. Bandwidth measures data volume per second, while compression ratio and storage capacity do not describe transmission delay.

Question 41Digital systems

Which description best characterises von Neumann architecture?

  1. The CPU reads each instruction directly from secondary storage at the moment it is needed.
  2. Program instructions and data are kept in physically separate memories that the CPU accesses independently.
  3. Instructions are stored permanently inside the CPU while data is kept only on the hard disk.
  4. Instructions and data are held in the same main memory and fetched by the CPU for execution. Correct answer.

Explanation

Von Neumann architecture is defined by the stored-program concept: both machine instructions and data reside in the same addressable main memory. The CPU fetches instructions and operands from that memory during the fetch-decode-execute cycle, so a single memory is shared rather than divided by content.

Question 42Digital systems

A student is editing a document in a word processor when the laptop battery fails and the machine powers off. Which property of RAM explains why unsaved edits are lost?

  1. RAM is volatile, so its contents are cleared when power is removed. Correct answer.
  2. RAM is read-only, so new edits cannot be written to it.
  3. RAM stores data magnetically, so a power loss erases the magnetic fields.
  4. RAM is non-volatile, so it keeps data only until the next restart.

Explanation

RAM is volatile semiconductor memory: it holds the programs and data currently in use, but it needs continuous power to maintain those values. When power is cut, the charge in its memory cells drains and unsaved edits held only in RAM disappear.

Question 43Digital systems

A user types a website's domain name into a browser. Which service translates that human-readable name into the numeric IP address needed to reach the server?

  1. FTP
  2. SMTP
  3. DHCP
  4. DNS Correct answer.

Explanation

The Domain Name System (DNS) is the internet's naming service. It resolves a domain name such as example.org into the IP address that routers use to deliver packets to the correct server.

Question 44Digital systems

Which statement best describes the function of cache memory in a computer system?

  1. It permanently stores the operating system and application files between sessions.
  2. It holds the program counter and current instruction register inside the CPU.
  3. It converts virtual memory addresses into physical addresses before each memory access.
  4. It is a small, fast memory holding recently used data to reduce average access time. Correct answer.

Explanation

Cache is a small block of fast memory placed close to the CPU, holding copies of recently or frequently accessed instructions and data. Because most programs show temporal and spatial locality, serving many requests from cache reduces the average time needed to obtain data compared with going to main memory.

Question 45Digital systems

A school database must store student names written in Latin, Arabic and Japanese scripts, plus emoji in free-text notes. Which character encoding approach is most appropriate?

  1. Seven-bit ASCII, which covers the standard English alphabet and control codes.
  2. Unicode, such as UTF-8, which assigns code points to characters across many writing systems. Correct answer.
  3. EBCDIC, which was designed for IBM mainframes and covers Latin characters.
  4. Morse code, which encodes letters as sequences of short and long signals.

Explanation

Unicode is designed to represent characters from the world's writing systems, including emoji, by assigning each a unique code point. UTF-8 is a variable-length Unicode encoding that remains backward-compatible with ASCII for basic Latin text while supporting the full range.

Question 46Digital systems

A two-input NAND gate is used in a control circuit. Which pair of input values makes the gate's output equal to 0?

  1. A = 0, B = 0
  2. A = 1, B = 1 Correct answer.
  3. A = 1, B = 0
  4. A = 0, B = 1

Explanation

A NAND gate outputs the inverse of an AND gate, so its output is 0 only when both inputs are 1. For all other input combinations, including 0-0, 0-1 and 1-0, the output is 1.

Question 47Digital systems

An uncompressed bitmap image is 200 pixels wide and 100 pixels high, using a colour depth of 8 bits per pixel. What is its approximate file size in kilobytes, taking 1 KB as 1000 bytes?

  1. 20 KB Correct answer.
  2. 2 KB
  3. 16 KB
  4. 160 KB

Explanation

The image has 200 x 100 = 20,000 pixels. At 8 bits per pixel it needs 20,000 x 8 = 160,000 bits, which is 160,000 / 8 = 20,000 bytes, or approximately 20 KB.

Question 48Digital systems

A computer has limited physical RAM but must run a program whose code and data exceed that RAM. Which explanation best describes how virtual memory makes this possible?

  1. The operating system adds extra RAM modules automatically when physical memory is exhausted.
  2. The OS swaps pages between RAM and disk, mapping virtual addresses to physical ones. Correct answer.
  3. The program is executed directly from secondary storage without ever being loaded into RAM.
  4. The CPU compresses every instruction before execution, so the program occupies less space in RAM.

Explanation

Virtual memory gives a program a logical address space that can exceed physical RAM. The operating system divides this space into pages and moves pages between RAM and secondary storage as needed; a page table maps virtual addresses to the physical frames currently holding them, and a page fault triggers a transfer when a page is absent.

Question 49Digital systems

A processor has a 20-bit address bus and no address multiplexing. How many distinct memory locations can it address directly?

  1. 20 squared, which is 400 locations
  2. 20 locations, one for each address line
  3. 20 multiplied by 2, which is 40 locations
  4. 2^20, which is 1,048,576 locations Correct answer.

Explanation

Each address line can carry one bit, so an n-bit address bus can represent 2^n distinct addresses. With 20 lines, the processor can distinguish 2^20 = 1,048,576 memory locations.

Question 50Digital systems

A medical imaging team archives scanned images and must restore every pixel exactly when the files are reopened. Which compression method is suitable?

  1. PNG, because it reduces file size without discarding any pixel data. Correct answer.
  2. JPEG, because it removes detail the human eye is unlikely to notice.
  3. MP3, because it compresses image data using perceptual models.
  4. MPEG, because it compresses each frame using motion prediction.

Explanation

Lossless compression reduces file size while allowing the original data to be reconstructed exactly, which is essential when no pixel may be altered. PNG uses lossless compression for images, so every pixel value is restored when the file is decompressed.