OS Interview Questions-6

1.What are the deadlock avoidance algorithms?
Ans: A dead lock avoidance algorithm dynamically examines the resource-allocation state to ensure that a circular wait condition can never exist. The resource allocation state is defined by the number of available and allocated resources, and the maximum demand of the process.There are two algorithms:
1. Resource allocation graph algorithm
2. Banker’s algorithm
a. Safety algorithm
b. Resource request algorithm

2. What are the basic functions of an operating system?
Ans : Operating system controls and coordinates the use of the hardware among the various applications programs for various uses. Operating system acts as resource allocator and manager. Since there are many possibly conflicting requests for resources the operating system must decide which requests are allocated resources to operating the computer system efficiently and fairly. Also operating system is control program which controls the user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

3.Explain briefly about, processor, assembler, compiler, loader, linker and the functions executed by them.
Ans :
Processor:–A processor is the part a computer system that executes instructions .It is also called a CPU
Assembler: — An assembler is a program that takes basic computer instructions and converts them into a pattern of bits that the computer’s processor can use to perform its basic operations. Some people call these instructions assembler language and others use the term assembly language.
Compiler: — A compiler is a special program that processes statements written in a particular programming language and turns them into machine language or “code” that a computer’s processor uses. Typically, a programmer writes language statements in a language such as Pascal or C one line at a time using an editor. The file that is created contains what are called the source statements. The programmer then runs the appropriate language compiler, specifying the name of the file that contains the source statements.
Loader:–In a computer operating system, a loader is a component that locates a given program (which can be an application or, in some cases, part of the operating system itself) in offline storage (such as a hard disk), loads it into main storage (in a personal computer, it’s called random access memory), and gives that program control of the compute
Linker: — Linker performs the linking of libraries with the object code to make the object code into an executable machine code.

4. What is a Real-Time System?
Ans : A real time process is a process that must respond to the events within a certain time period. A real time operating system is an operating system that can run real time processes successfully

5. What is the difference between Hard and Soft real-time systems?
Ans : A hard real-time system guarantees that critical tasks complete on time. This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it. 

A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes. As in hard real time systems kernel delays need to be bounded

6. What is virtual memory?
Ans : A virtual memory is hardware technique where the system appears to have more memory that it actually does. This is done by time-sharing, the physical memory and storage parts of the memory one disk when they are not actively being used

7. What is cache memory?
Ans : Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data

8.Differentiate between Complier and Interpreter?
Ans : An interpreter reads one instruction at a time and carries out the actions implied by that instruction. It does not perform any translation. But a compiler translates the entire instructions.

9.What are different tasks of Lexical Analysis?
Ans : The purpose of the lexical analyzer is to partition the input text, delivering a sequence of comments and basic symbols. Comments are character sequences to be ignored, while basic symbols are character sequences that correspond to terminal symbols of the grammar defining the phrase structure of the input

10. Why paging is used?
Ans : Paging is solution to external fragmentation problem which is to permit the logical address space of a process to be noncontiguous, thus allowing a process to be allocating physical memory wherever the latter is available.