An operating system (OS) is a software program that manages computer hardware and software resources and provides common services for computer programs. It acts as an intermediary between computer applications and the underlying hardware, controlling the execution of software programs and managing tasks such as memory allocation, input/output operations, and device management. Preparing for a fresher’s interview or an advanced-level operating system interview questions, our set of questions will help you. The questions cover various topics like types of OS, memory management, Scheduling algorithms, Device management and I/O operations, and Distributed systems and network protocols. With our OS interview questions and answers, you will be prepared to face any interview.
An operating system is defined as "a program that runs continuously on the computer (usually referred to as the kernel), with all other programs being application program." A computer system is divided into four components: hardware, operating system, application programs, and end users. An operating system provides abstractions including:
An operating system serves as a conduit between the user and the hardware of the system. The operating system provides a platform for users to easily execute application programs. An operating system's job is to provide services such as memory management.
An important task of an operating system is -
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An operating system performs tasks like managing the files and processing and allocating the memory. Here are the types of operating systems that are widely used as follows-
Operating systems like Windows and Linux, run on multiprocessors. Multiprocessing refers to the execution of multiple concurrent software processes in a system as opposed to a single process at any one instant. To increase the performance of an OS it uses the multiprocessor on a system.
Types of multiprocessor systems -
A variety of disk-organization techniques, collectively called redundant arrays of expensive disks(RAIDs) are commonly used to address performance and reliability issues. RAID composed of small, cheap disks were viewed as a cost-effective alternative to large, expensive disks. RAID concepts have been extended to tape drives, and for broadcasting of data.
The kernel is a medial component of an operating system that manages the operations of the computer system and the hardware. Kernel acts as a bridge between the applications and data processing performed at hardware using the interprocess communication and the system calls. The kernel does tasks like disk management, task management and file management.
Virtual memory is memory allocation in which secondary memory can be addressed in the main memory. Virtual Memory is a space where a large form of data is stored in the form of paging. Virtual memory can be implemented with the help of -
Expect to come across this popular operating system interview questions and answers for freshers.
A graphical User Interface:
A pipe acts as a conduit allowing two processes to communicate. Pipes were one of the first IPC mechanisms in UNIX systems and it provides similar ways for processes to communicate with one another. Two common types of pipes used on both UNIX and Windows systems are ordinary pipes and named pipes. The pipe allows two processes to communicate in a standard Producer consumer fashion; the producer writes to one end and the consumer reads from the other end.
The operating system is provided for the convenience of the programmer, to make the programming task easier.
Here, is the view of operating system services.
Only one task may be completed at a time by the process, thanks to a single thread of control. For instance, the user cannot utilize the spell checker and input characters at the same time in the same process. Many contemporary operating systems have expanded the idea of a process to let it execute numerous threads at once, allowing it to handle multiple tasks concurrently.
The PCB is enlarged on systems that support threads to provide details for each thread. To support threads, additional adjustments must be made throughout the system.
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The features of the real-time operating system are -
FCFS stands for FIRST_COME, FIRST-SERVED (FCFS) SCHEDULING
Requests are scheduled in the order in which they arrive in the system. The list of pending requests is organized as a queue. An example of First Come First Serve scheduling is a batch processing system in which jobs are ordered according to their arrival times and the results of a job are released to the user immediately upon completion of the job. The following example illustrates the operation of an FCFS scheduler.
Table 7.1 Process for scheduling
Id ta w
Process in the system (FCFS order)
P1 3 1.00
P2 4 1.33
P3 8 1.60
P4 9 4.50
P5 8 2.67
ta= 7.40 seconds
W = 2.22
Figure 7.1 illustrates the scheduling decisions made by the FCFS scheduling policy for the processes of Table 7.1. Process P1 is scheduled at time 0. The pending list contains P2 and P3 when P1 completes at 3 seconds, so P2 is scheduled. The Completed column shows the id of the completed process and its turnaround time(ta) and weighted turnaround(w). The mean values of ta and w are shown below the table. The timing chart shows how the processes operated.
It is a pre-emptive algorithm. It is mostly designed for time-sharing algorithms. This algorithm is similar to the FCFS algorithm. But, in RR scheduling are added which lets the system enables the system between the process.
Round Robin is mostly used when conducting the basic tests to ensure that new balancers have been configured correctly or not. It is the hybrid model which works as a clock-driven approach.
A zombie process is a process that has completed its execution but still has an entry in the process table to report to its parent process. Before being removed from the process table, a child process always becomes a zombie. The parent process reads the child process's exit status and removes the child process entry from the process table.
In a multiprogramming environment, several processes may compete for a finite number of resources. A process requests resources; if the resources are not available at that time, the process enters a wait state. It may happen that waiting processes will never again change state because the resources they have requested are held by other waiting processes.
When all four of the following criteria are met concurrently in a system, a deadlock might happen.
Thrashing occurs when a computer's performance degrades or collapses. When a system spends more time processing page faults than executing transactions, it is said to be thrashing. While processing page faults is required to reap the benefits of virtual memory, thrashing is detrimental to the system. More transactions require processing from the paging device as the page fault rate increases. The queue at the paging device grows, resulting in a longer response time for a page fault.
Bélády's anomaly occurs when some page replacement policies increase the number of page frames, resulting in an increase in the number of page faults. It happens when you use First in First Out page replacement.
An illustration of Bélády's anomaly. Nine-page faults occur when three-page frames are used. Ten-page defects happen when the number of page frames is increased to four. Page errors are highlighted in red. This can be attributed to "Penny Wise, Pound Foolish" behavior.
A thread is equipped with its program counter (PC), register set, and stack space. Threads, unlike processes, are not independent of one another. As a result, threads share their code section, data section, and OS resources such as open files and signals with other threads.
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Semaphore is a variable that has an integer value upon which the following three operations are defined:
Concept of operation:
Two or more processes can cooperate by means of simple signals, such that the process can be forced to stop at a specified place until it has received a specific signal. For signaling, special variables called semaphores, a process executes the primitive wait(s); if the corresponding signal has not yet been transmitted, the process is suspended until the transmission takes place.
The wait and signal primitives are assumed to be atomic; that is, they cannot be interrupted, and each routine can be treated as an indivisible step.
It is a mechanism that enables the execution of processes even when memory isn't fully utilized. Programs can be larger than physical memory, which is the key advantage that is immediately apparent in this system. User logical memory is divided from physical memory into virtual memory. Because of this split, programmers can be given access to a very large virtual memory, even when just a tiny physical memory is available.
Demand paging is frequently used to implement virtual memory. It can be used in a segmentation system as well. Virtual memory can also be provided using demand segmentation.
The goal of a DOS assault is to prevent computers from being used for any meaningful tasks by clogging them up so poorly that they cannot be accessed or damaged. This exploit manifests itself most obviously in tight loops that repeatedly request system services. DOS assaults can also use social engineering, including Internet chain letters that instruct recipients to "share this instantly to 10 of your friends, and then go to a certain URL," which jams up both the web server that everyone is directed to and the Internet mail system.
Security systems that lock accounts after a certain number of failed login attempts are subject to DOS attacks which repeatedly attempt logins to all accounts with invalid passwords strictly in order to lock up all accounts.
The send and receive system calls are used to communicate between processes but there are different design options for implementing these calls. Message passing may be either blocking or non-blocking – also known as synchronous and asynchronous.
This is a frequently asked OS technical interview questions.
An operating system is loaded or booted as opposed to being installed, which is often a one-time process. (Buying a computer with an operating system already set up is not essential.) It's possible that you'll be asked to choose particular configuration settings or options during the operating system installation. Your operating system is installed and ready to boot (load) into random access memory, which is more accessible to the microprocessor and more quickly usable than the hard disc.
When you try to install an operating system, it is usually configured so that when you turn on the computer, the system boots up as well. If you run out of storage (memory), or if the operating system or an application program encounters an error, you may get an error message or your screen may "freeze" (you will be unable to perform any actions). You may need to restart the operating system in these cases.
When you turn on your computer, the operating system is likely to boot (load into RAM) in the following sequence:
It is an interprocess communication (IPC) mechanism that allows independent but cooperating tasks (that is, active classes) to communicate with one another within a single CPU.
Throughput is the number of units of information a system can process in a given amount of time. It is broadly applied to systems ranging from computer and network systems to organizations.
The functions of Operating System are :
A process is a running program instance.
It is a collection of instructions designed to complete a specific task.
Processes are active entities because they are created during execution and loaded into main memory.
Because it is stored in secondary memory, the program is a passive entity.
It has a finite lifespan because it is terminated once the task is completed.
It exists in a single location and will exist until it is deleted.
During its lifetime, it requires a lot of resources, such as a CPU, memory address, and I/O.
It does not require any resources; it only requires memory space to store the instructions.
For a limited time, resources (CPU Cycle) are assigned to a process.
Once resources (CPU Cycle) are assigned to a process, it holds them until the process completes its burst time or switches to the waiting state.
It can be interrupted at any time.
It can't be interrupted until it dies or its time runs out.
A low priority process may starve if a high priority process frequently arrives in the ready queue.
If a process with a long burst time consumes CPU, a subsequent process with a shorter burst time may suffer.
No cost associated
CPU utilization is high
It is low in non-preemptive scheduling.
Waiting time is less
Waiting time is high
In preemptive scheduling, response time is less
In non-preemptive scheduling waiting time is high.
A socket is defined as an endpoint for communication. A pair of processes communicating over a network employs identify a pair of sockets-one for each process. A socket is identified by an IP address with a port number. This way we can able to identified the personal computer.
Sockets typically employ client-server architecture. The server listens to a specific port for incoming client requests. The server accepts a connection from the client socket after receiving a request to complete the connection. Severs implementing specific services (such as telnet, FTP, and I-HTTP) listen to well-known ports (a telnet server listens to port 23; an FT server listens to port 21; and a web, or HTTP, server listens to port 80). All ports below 1024 are considered well-known; we can use them to implement standard services. When a client process initiates a request for a connection, it is assigned a port by its host computer. This port is some arbitrary number greater than 1024.
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Starvation: Indefinite blocking or starvation is a phenomenon associated with Priority scheduling algorithms in which a process ready for the CPU (resources) can wait indefinitely due to low priority. A steady stream of higher-priority processes in a heavily loaded computer system can prevent a low-priority process from ever receiving the CPU. According to rumors, Priority Scheduling was used in IBM 7094 at MIT in 1967, and they discovered a low-priority process that had not been submitted until 1973.
Aging: Aging is a method of gradually raising the priority of processes that have been waiting in the system for a long time. For example, if the priority range is 127 (low) to 0, we could raise the priority of a waiting process by 1 every 15 minutes. Even if a process had a starting priority of 127, it would take no more than 32 hours for the priority 127 processes to age to a priority-0 process.
Assembly language is a type of low-level language and program it is more commonly known as an assembler, with the inverse program known as a disassembler.
An assembler converts the assembly codes into binary codes and then it assembles the machine understandable code into the main memory of the computer, making it ready for execution.
Functions of an assemblers are given below:
Process can be defined as:
A process generally also includes the process stack, which contains temporary data, and a data section, which contains global variables.
As a process executes, it changes the state
Spooling is the temporary storage of data for use and execution by a device, program, or system. Data is sent to and stored in memory or other volatile storage until it is requested for execution by a program or computer.
SPOOL stands for concurrent peripheral operations online. In most cases, the spool is kept in physical memory, buffers, or I/O device-specific interrupts on the computer. The spool is processed in ascending order, using a first-in, first-out (FIFO) algorithm.
divided into pages, which are identical-sized blocks. The pages of a process are loaded into any free memory frames prior to execution. Each address produced by the CPU has two components: a page number (p) and a page offset (d). A page table's index is created using the page number. Each page in physical memory has a base address, which is contained in the page table. The physical address that is supplied to the memory unit is defined by this base address and the gauge offset.
The page size is defined by the hardware. The size of a page is typically a power of 2 varying between 512 bytes and 8192 bytes per page, depending on the computer architecture. The selection of a power of 2 as a page size makes the translation of a The high order m-m bits of a logical address identify the page number, while the n-low order bits designate the page offset when the logical address space is 2m and the page size is 2n addressing units. Thus the logical address is as follows:
Page number page offset
Where p is an index into the page table and d is the displacement within the page.
It is the mechanism provided by the operating system for communicating between processes This communication could include a process informing another process of an event or data being transferred from one process to another.
Pipe: A pipe is a unidirectional data channel. A two-way data channel between two processes can be created using two pipes. This employs conventional input and output methods. Pipes are used in both POSIX and Windows operating systems.
Socket: The socket is the network endpoint for sending and receiving data. This applies to data sent between processes on the same computer as well as data sent between computers on the same network. For interprocess communication, most operating systems employ sockets.
There are three different methods for dealing with the deadlock problem:
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There are two types of fragmentation i.e. Internal fragmentation and External Fragmentation.
A Process Scheduler assigns different processes to the CPU based on specific scheduling algorithms. There are six popular process scheduling algorithms that we will discuss in this chapter.
First-come, first-served basis (FCFS), Priority of Shortest-Job-Next (SJN), Scheduling Shortest Remaining Time, Round Scheduling Robin(RR), Scheduling of Multiple-Level Queues.
The kernel is the central component of an operating system that manages computer and hardware operations.
Types of Kernel:
First Come First Serves
The non-preemptive scheduling algorithm is first come, first served (FCFS).
The preemptive scheduling algorithm is Round Robin (RR).
FCFS has the least amount of overhead.
While RR has a small overhead because it must record the time elapsed and then switch the process, this causes an overhead.
In the time sharing system, FCFS is inconvenient to use.
It is primarily intended for the time sharing system and thus is simple to use.
In general, the average waiting time in the First Come First Served Scheduling Algorithm is not short.
The Round Robin Scheduling Algorithm has a low average waiting time.
The process is simply carried out in the order in which they arrive at FCFS.
In terms of processing, it is similar to FCFS, but it employs time quantum.
Compiler: A compiler is a computer program that reads code written in a high-level language such as FORTRAN, PL/I, COBOL, and so on. It is capable of translating it into the same program in a low-level language such as machine language. The compiler also detects various errors that occur during the compilation of a program.
Interpreter: An interpreter is a program that directly executes programming code rather than simply translating it into another format. It sequentially translates and executes programming language statements. In comparison to a compiler, an interpreter takes less time to interpret a source program.
Every machine in a cluster runs a distributed lock manager (DLM), which has an identical copy of a cluster-wide lock database. A DLM, in this way, allows software applications distributed across a cluster on multiple machines to synchronize their access to shared resources.
Compaction is a memory management technique that compacts a running system's free space in order to reduce fragmentation and improve memory allocation efficiency. Many modern operating systems, including Windows, Linux, and Mac OS X, use compaction. As shown in the diagram, we have some used memory (in black) and some unused memory (white color). The memory that has been used is combined. All of the empty spaces are combined. This is known as compaction. This is done to avoid fragmentation, but it consumes an inordinate amount of CPU time.
Static Linking: The process of incorporating the code of a program or library into a program so that it is linked at compile time is known as static linking. Because the library's code is copied into the executable file, it generally results in faster program startup times. It makes debugging programs easier because all symbols are resolved at compile time.
Dynamic Linking: The library is not copied into the program's code in this case. Instead, the program contains a reference to the location of the library. When you run the program, it will load the library from that location.
Some operating systems were created in the 1950s when computers could only run one program at a time. Operating systems are critical because they are in charge of everything from memory control and allocation to recognizing input from external devices and transmitting output to computer displays. Later in the sometimes, some computers included many software programs, sometimes referred to as libraries, that were linked together to form the foundation of today's operating systems. Get to Know more about the best software development courses by enrolling with us today and learning all aspects of software development.
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