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WGU D686 OPERATING SYSTEMS FOR
COMPUTER SCIENTISTS OA
CERTIFICATION SCRIPT 2026 QUESTIONS
WITH SOLUTIONS GRADED A+
◍ How many threads can a process have?. Answer: One or more (can be multiple).
◍ What is a DDoS attack?. Answer: Distributed Denial-of-Service—multiple systems attack a target, overwhelming it.
◍ Command Line Interface. Answer: a user types commands represented by short keywords or abbreviations or presses special keys on the keyboard to enter data and instructions
◍ Device Driver. Answer: An operating system component that provides uniform access to various devices and manages I/O to those devices. Ensure the device works on all known operating systems
◍ Status Information. Answer: A system service. Some programs simply ask the system for the date, time, amount of available memory or disk space, number of users, or similar status information.
◍ What is a denial-of-service (DoS) attack?. Answer: An attack that disrupts system services by overwhelming resources.
◍ Sharing. Answer: The act of linking the same copy of a module to multiple other
modules. Sharing improves memory utilization by allowing multiple processes to share common routines or services (Ex: compilers, editors, word processors), or common data (Ex: dictionaries). Sharing is possible under both static and dynamic linking
◍ What is a back door?. Answer: A hidden way to bypass normal authentication and gain unauthorized access to a system.
◍ What is a capability list?. Answer: Specifies which resources a user/process can access.
◍ read-only memory (ROM). Answer: It's a type of computer storage containing non-volatile, permanent data that, normally, can only be read, not written to.
◍ Which operating system feature is responsible for selecting a process to execute?. Answer: Scheduler
◍ Trapdoor (aka Backdoor). Answer: Mechanism that bypasses user authentication. Ex: A systems programmer could modify the login utility to accept a specific user without requiring a password, thus permitting unauthorized access to the system at a later time
◍ Global data. Answer: data items that are automatically available to all modules throughout the system
◍ What is the difference between a virus and a worm?. Answer: Virus attaches to files and needs user action; worm spreads automatically without user intervention.
◍ What is the recommended Linux file system for flash drives?. Answer: EXT2 (no journaling, less write wear).
◍ What is volatile memory?.
Answer: In general, any computer, no matter the size, that provides resources to other computers.
◍ What is a Master File Table (MFT)?. Answer: NTFS metadata table for all files.
◍ How can you access Dropbox?. Answer: Web browser, desktop app, mobile app.
◍ Fragmentation. Answer: In the context of a hard disk, is a condition in which the contents of a single file are stored in different locations on the disk rather than in a contiguous space
◍ Supervisor Call or Kernel Call. Answer: Provide the interface between the OS kernel and the higher-level software.
◍ Locations where firmware can be stored. Answer: Flash Memory, Read-only memory
◍ What is the difference between stream cipher and block cipher?. Answer: Stream cipher encrypts data one bit/byte at a time; block cipher encrypts fixed-size blocks.
◍ What is the main difference between EXT2 and EXT3?. Answer: EXT3 adds journaling for reliability.
◍ Main difference between trap and interrupt. Answer: The difference between ____(1) and ____(2) is that a __(1) is triggered by a user program to invoke OS functionality.An ___(2) is triggered by a hardware device to allow the processor to execute the corresponding interrupt handler routine.
◍ What is asymmetric encryption?. Answer: Uses a public key to encrypt and a private key to decrypt.
◍ Least Recently Used (LRU). Answer: It selects the page that has not been referenced for the longest time.
◍ What is physical memory?. Answer: Actual RAM; limited by hardware size.
◍ What is a page frame?. Answer: It is a fixed-size contiguous block of physical memory identified by a single number, the page frame number.
◍ What is session hijacking?. Answer: An attacker takes over a valid user session, often by stealing session cookies or tokens.
◍ Interrupt. Answer: It is triggered by a hardware signal sent to the CPU from an external device
◍ Magnetic Storage Devices. Answer: Includes magnetic tape, floppy disks and hard-disk drives.
◍ Stack Pointer (SP). Answer: Points to a stack holding return addresses, procedure or function parameters, and local variables; it is accessed when a procedure or function is called or an interrupt is serviced.
◍ Backdoor. Answer: Mechanism that bypasses user authentication. Ex: A systems programmer could modify the login utility to accept a specific user without requiring a password, thus permitting unauthorized access to the system at a later time.
◍ What is defense in depth?. Answer: Multiple layers of security controls throughout an IT system.
◍ Which generation of computers were large-scale integrated circuits used to develop personal computers for desktop and laptop operating systems?. Answer: The fourth generation
◍ Uses of Mainframe as a computing environment. Answer: Supports a high volume of data processing and the management of
◍ Resource Allocation. Answer: Related to ensuring the efficient operation of the system and is unrelated to providing services to user programs
◍ What is a page in memory management?. Answer: A page is a fixed-size contiguous block of a logical address space identified by a single number, the page number.
◍ Critical Section. Answer: a piece of code that only one thread can execute at a time
◍ What is a boot partition?. Answer: Section of disk containing files needed to start the operating system.
◍ Device Management. Answer: It is a system call category-request device, release device-read, write, reposition-get device attributes, set device attributes-logically attach or detach devices
◍ Multi-threaded process. Answer: multiple threads within a single process, each having their own program counter, stack and set of registers, but sharing common code, data, and certain structures such as open files.
◍ Shared Memory. Answer: Communications may be implemented via _____, in which two or more processes read and write to a shared section of memory
◍ What are the two main authentication techniques?. Answer: Password-based and biometric-based authentication.
◍ What is linked allocation?. Answer: Each file block points to the next.
◍ Shared-memory model. Answer: An interprocess communication method in which multiple processes share memory and use that memory for message passing.
◍ What is a thread?. Answer: A thread is a lightweight subprocess.It is a separate path of execution.It is called separate path of execution because each thread runs in a separate stack frame.
◍ Cache Memory. Answer: A type of memory used to temporarily store frequently used data or programs for quick access; similar to RAM but faster.
◍ What is a Trojan horse?. Answer: Malicious software disguised as legitimate, often used to gain unauthorized access.
◍ Short-term scheduler. Answer: selects from among the processes in ready queue, and allocates the CPU to one of them
◍ What is a process?. Answer: A program in execution.
◍ Next-fit. Answer: Starts each search at the point of the last allocation.
◍ Flash Memory. Answer: Non-volatile memory that can be read from and written to. It is suitable for secondary storage.
◍ challenge response. Answer: a sort of public duel whereby one person offers a word, gesture, question or action and the other must respond in a way that answers in equal measure or ups the ante.
◍ Advanced Encryption Standard (AES). Answer: A symmetric cipher that was approved by the NIST in late 2000 as a replacement for DES.
◍ What is a Boot Control Block (BCB)?. Answer: Contains boot information for a volume.
Answer: A system service. These programs provide the mechanism for creating virtual connections among processes, users, and computer systems. They allow users to send messages to one another's screens, to browse web pages, to send e-mail messages, to log in remotely, or to transfer files from one machine to another.
◍ Memory Compaction. Answer: The systematic shifting of modules in memory, generally in one direction, to consolidate multiple disjoint holes into one larger hole.
◍ What is a valid-invalid bit?. Answer: Indicates if a page is in memory (valid) or not (invalid).
◍ How many processes can a PCB represent?. Answer: One.
◍ System Call. Answer: It is implemented as a library function, which sets up the necessary parameters for the requested operation and issues a corresponding supervisor call.
◍ Mutual Exclusion. Answer: Only one process may be executing within a critical section
◍ Virtual Address. Answer: A virtual address does not represent the actual physical location of an object in memoryThe system maintains a page table for each process, which is an internal data structure used to translate virtual addresses into their corresponding physical addresses. Each time a thread references an address, the system translates the virtual address to a physical address.
◍ What is the difference between breach of confidentiality and breach of integrity?. Answer: Confidentiality breach exposes private data; integrity breach alters or corrupts data.
◍ Shells.
Answer: The name of command line interpreters when multiple are available in an operating system
◍ What does the Windows system call interface use?. Answer: Uses API (Application Programming Interface) to standardize calls for all programs.
◍ What is a shared lock?. Answer: Multiple processes can read.
◍ What is clustered allocation?. Answer: Files stored in clusters of blocks.
◍ System Call. Answer: A request from an application for an OS service
◍ What is a mount table?. Answer: Tracks mounted file systems.
◍ Role of operating system. Answer: The operating system (OS) is the software that runs on the bare hardware of a computer and provides essential support for users to develop and use applications in the most efficient and safe manner.
◍ 50% rule in external fragmentation. Answer: If the probability of finding an exact match for a request approaches 0, one third of all memory partitions are holes and two thirds are occupied blocks. Formally, n = 0.5 m, where n is the number of holes and m is the number of occupied block
◍ disk block. Answer: a fixed sequence of bytes on the disk, which can only be accessed as a single unit using low-level read-block and write-block operations
◍ What is LRU in page replacement?. Answer: Least Recently Used; replaces page not used for longest time.
◍ System Service. Answer: An application included with an operating system to provide
specified time to perform some destructive action. The main use of a logic bomb is for blackmail or an act of revenge.
◍ Working Set of a process. Answer: At time t, it is the set of pages referenced during the past d memory operations preceding t.
◍ Command Line Interface. Answer: Allows combining multiples programs using the output from one as the input to another
◍ Aging register. Answer: It is associated with a page and is shifted periodically to the right by 1 bit. Unless the most significant bit is set to 1, the page is aging in the sense that the associated register value is steadily decreasing.
◍ RSA Encryption. Answer: It is the most common internet encryption and authentication system. The system used an algorithm that involves multiplying two large prime numbers to generate a public key, used to encrypt data and decrypt an authentication, and a private key, used to decrypt the data and encrypt an authentication.Asymmetric
◍ What is a shaft in disk terminology?. Answer: Central axis spinning platters.
◍ Principle of locality. Answer: Locations accessed recently are more likely to be accessed again than locations accessed in the distant past
◍ What is a man-in-the-middle attack?. Answer: An attacker secretly intercepts and possibly alters communications between two parties who believe they are directly communicating with each other.
◍ Replacement Algorithm. Answer: It selects the page that will not be referenced for the longest time in
the future.
◍ File Management. Answer: It is a system call category OR a system utility
◍ Page Fault Consequences. Answer: Results in a significant overhead, which increases the average access time to memory.
◍ virtual address. Answer: An address that corresponds to a location in virtual space and is translated by address mapping to a physical address when memory is accessed.
◍ external fragmentation. Answer: The loss of usable memory space due to holes between allocated blocks of variable sizes.
◍ What is a cylinder?. Answer: Set of tracks at same position on all platters.
◍ Thrashing. Answer: It is an execution state during which most of the time is spent on moving pages between the memory and the disk while the CPU is mostly idle and no process is making any real progress.
◍ System Calls. Answer: These are generally available as functions written in C and C++, although certain low-level tasks (for example, tasks where hardware must be accessed directly) may have to be written using assembly-language instructions.
◍ What is a program counter?. Answer: Register holding address of next instruction.
◍ preemptive scheduling. Answer: It is used when a process switches from running state to ready state or from the waiting state to ready state
time. When multiple physical CPUs are available, the processes may execute in parallel. On a single CPU, concurrency may be achieved by time-sharing.
◍ Internal Fragmentation. Answer: a situation in which a partition is only partially used by the program; the remaining space within the partition is unavailable to any other job and is therefore wasted.
◍ Which operation causes a process to be blocked?. Answer: Input/Output process
◍ What is a computer program in execution called?. Answer: A process
◍ Least Recently Used (LRU). Answer: A replacement scheme in which the block replaced is the one that has been unused for the longest time.
◍ Which principle allows processes to execute cooperatively on a single CPU?. Answer: Non-preemptive scheduling
◍ Deadlock Detection. Answer: A set of methods intended to ensure that at least one of the necessary conditions for deadlock cannot hold.
◍ Process. Answer: It is an instance of a program being executed by an OS. Ex: When a user opens a new application like a web browser or text editor, the OS creates a new process.
◍ Virtual Address components. Answer: Segmentation and Page
◍ Sandbox. Answer: It is a small area of memory within which a program may execute and which guarantees that the program cannot access and jump to any
location outside of the designated area. A sandbox consists of two areas, one for the executable code and another for data.
◍ Linking. Answer: The act of resolving external references among object modules and can be done statically, before loading, or dynamically, while the program is already executing.
◍ Referenced bit (r-bit). Answer: It is associated with a page and is set automatically by the hardware whenever the page is referenced by any instruction.
◍ Program Counter (PC). Answer: The register that contains the address of the next instruction to be executed.This is what each thread of a multi-threaded process uses to access shared code
◍ What is a file directory or folder?. Answer: Container for files.
◍ SSD vs HDD. Answer: A secondary storage device based on mechanical components, including spinning magnetic media platters and moving read-write heads. (HDD)SDD does not contain magnetic coatings and is more reliable. It does not need power to retain data
◍ Message Passing. Answer: In interprocess communication, a method of sharing data in which messages are sent and received by processes. Packets of information in predefined formats are moved between processes or between computers.
◍ What is two-factor authentication?. Answer: Requires two forms of verification, e.g., password and code sent to phone.
◍ What is an exclusive lock?. Answer: Only one process can read/write.
◍ Virtualization. Answer: It is the act of creating the illusion of having one or more objects with more desirable characteristics than the real object. OSs rely on virtualization to create virtual CPUs, memory, I/O devices, and other system components that facilitate the work of programmers and users.
◍ What is the difference between global and local replacement?. Answer: Global allows page replacement from any process; local restricts to process's own pages.
◍ Effective access time. Answer: It is the average time to access memory in the presence of page faults.
◍ login spoofing. Answer: Approach where a legitimate user presents a fake login screen to an unsuspecting user, who unwittingly supplies a valid login name and password to the imposter program. A possible solution to prevent login spoofing is to display the login screen only after the user has typed in a special character sequence that automatically invokes the OS and which a user program cannot intercept (Ex: CTRL-ALT-DEL).
◍ Locks. Answer: Ensures the integrity of the data being shared and operating systems often provide system calls allowing ___ to happen. No other process can access the data until it is released
◍ What is a logic bomb?. Answer: Malicious code that triggers a harmful action when specific conditions are met.
◍ What is external fragmentation?. Answer: Wasted space between allocated blocks that can't be used.
◍ Device Driver. Answer: It is a device-specific program that implements I/O operations,
requested by user applications or the OS, by interacting with the device controller. Since devices vary greatly in speed, latency, and the size of data being transmitted, the ability to perform random vs sequential access, and other aspects, device drivers are supplied by the device manufacturers.
◍ Supervisor Call or Kernel Call. Answer: Privileged instruction that automatically transfers execution control to a well-defined location within the OS kernel
◍ System Service. Answer: The additional functionality provided by a program that has been incorporated into and started as part of the operating system.
◍ What is a page table?. Answer: It is an array that keeps track of which pages of a given logical address space reside in which page frames. Each page table entry corresponds to one page and contains the number or the starting address of the frame containing the page.
◍ Page Fault. Answer: It is an interrupt that occurs when a program attempts to reference a non-resident page. The interrupt triggers the operating system to find the page on disk, copy the page into a frame, and set the present bit to 1.
◍ What is the Working-Set Model?. Answer: Tracks active set of pages used by process to reduce faults.
◍ Random Access Memory (RAM). Answer: Computer location where instructions and data are stored on a temporary basis. This memory is volatile, rewritable. Can be called Main Memory
◍ What is the difference between PC and PCB?. Answer: PC points to instruction; PCB stores all process info.
◍ Kernel Mode. Answer: The CPU state where both privileged and non-privileged
