CS604 FAQs and Glossary by Eagle Eye

CS604 - Operating Systems FAQs

Question: Is there any concrete reason behind selecting Linux as a major OS for study in this course instead of Windows because most of us has windows already installed and we are also familiar with it, kindly explain

Answer: Yes. Linux is open source. You have complete code of Linux operating system whereas in Windows you do not have the privilege to see its code. While programming in C in the Linux environment you get a better understanding of the OS concepts. Question: i have purchased a Fedora Core 2 redhat 11 for linux OS which consists of 4 CDs, is it ok and tell me is there any specific system requirements and like that etc, kindly explain.

Answer: Yes it is fine. I think you will find the system requirements on the CD cover. I think that 512 RAM and 1 plus Gb processor will be OK Question: Please provide us the link of Virtual Machine for which I would be able to install both Operating System Window XP and Linux.

Answer: You can download the VMware from the following link: As far as Linux is concerned, try to get the cd of Linux from the market as it is not easy to download complete Linux from internet. But if you have fast internet then you may try Question: Tell me the name of recommended book or reference books for this subject.

Answer: Operating Systems by Silberschatz is the text book. For reference, consult Operating System by Tannenbaum Moreover consult CS604 handouts. Question: kindly explain a major difference between hard & soft real time systems with the help of an example.

Answer: Real time systems need to provide the desired output in the given amount of time. Hard real time systems are those that guarantees the critical tasks should be completed within specified time. For example you have a system of ECG where a patients pulse is seen on the monitor screen. The working of ECG is critical and hence it must show the desired output in the given amount of time and delay in getting the output my lead to serious consequences therefore it should be guaranteed that the machine should be able to provide the output in specific amount of time. Whereas Soft real time system are less restrictive. Though getting the output in these systems are also important but not so critical as compared to hard real time systems. Here one task can get priority over other task. For example if you are using a real time system in a washing machine then the output of the system ( e.g buzzer alarm) is not so critical and it may happen that this system allows washing machine to stop first and then rung the Buzzer instead of normal flow of ringing the Buzzer before stopping the machine. Question: What is an efficient operating system, what is the main parameter to judge the efficiency of an OS?

Answer: We can call an OS to be efficient if it can perform all the necessary functions like resource management, memory management, CPU and process scheduling etc. in an efficient manner. Question: what was the main reason that user could not interact with a multi programmed batched computer system? Was it only due to slow response?

Answer: The main reason is that the operating system design did not allow the user to interact with the running jobs. Later Kernel were designed in such a way that they provided the facility of interactivity along with multiprogramming. Question: Historically, single user systems were evolved before or after time sharing systems?

Answer: Single user systems were invented before time sharing systems. Question: Kindly give an example of a signal ?

Answer: A signal is an event to get the attention of a process. . A signal can be send from one process to an other process. For example if a file exceeds limits then the process may be asked to produce the output until the file size is increased. Similarly you can use ctr+z command on Linux shell to stop the running process. Question: Is this necessary that all the privileged instructions reside in kernel area of memory.

Answer: Yes. Privileged instructions can be used by Application programmer with the help of system calls.

Answer: Computer systems stores and process data in the form of bits; 0 and 1. A 32 bit means the size of the word

Answer: Computer systems stores and process data in the form of bits; 0 and 1. A 32 bit means the size of the word

Question: What are Non-privileged instructions?

Answer: The instructions that are not related to the hardware operations are termed as non-privileged instructions. For example manipulating the user's data. Question: What is the difference between MEMORY SPACE and ADDRESS SPACE?

Answer: They are both same thing by meaning nut in lecture # 3 handouts address space refers to the region in the memory that a process is allowed to access whereas memory pace is region of the memory where operating system resides. Question: What is the difference between USER PROCESS and SYSTEM PROCESS?

Answer: User process is the one created by the user while the process created by the Operating System is called System process. Question: What is the difference between USER PROCESS and SYSTEM PROCESS?

Answer: User process is the one created by the user while the process created by the Operating System is called System process. Question: What is the difference between PROCESS SYNCHRONIZATION and PROCESS COMMUNICATION?

Answer: Process Synchronization means that process working should be synchronized so that processes should finish their working in a desired order so that they can contribute in producing the correct result whereas Process communication is the communication of processes between them known as inter process communication. Question: What is DEADLOCK?

Answer: Deadlock is a condition in the system in which a process A is waiting for the resources held by process B and process B is waiting for the resources held by process A Question: How STACK is defined and maintained in main memory?

Answer: A stack is created in the main memory so as to keep the necessary output of the processes when required. Question: What is FILE SYSTEM? What is the difference between FAT32 and NTFS file system? LINUX use which FILE SYSTEM?

Answer: File System is a system of managing the files in the computer system.FAT, FAT 32, NTFS are used in Windows operating system. They are different with respect to performance, storage capacity of files etc. Linux uses ext2 file system. Question: What is FILE SYSTEM? What is the difference between FAT32 and NTFS file system? LINUX use which FILE SYSTEM?

Answer: File System is a system of managing the files in the computer system.FAT, FAT 32, NTFS are used in Windows operating system. They are different with respect to performance, storage capacity of files etc. Linux uses ext2 file system. Question: What is the difference between BUFFERING and CASHING?

Answer: Buffer is a temporary memory for holding a specific data (input or output) for some period of time. Some devices also have buffer with them for example a keyboard, you may have experienced that sometimes you type alphabet letters but they do not readily display on the screen and stay in the buffer until the CPU becomes free to process it. Cache is a fast memory used for readily accessing the data. Question: What is the difference between BOURNE SHELL and DOS?

Answer: DOS is Disk Operating System whereas Shell is a terminal (like a command prompt) in Linux/Unix. Question: What is the difference between LIBRARY CALL and SYSTEM CALL?

Answer: Library calls are made by library functions which are defined in the header files of the library whereas System calls are defined by the operating system and provide an interface to the application programmers to use the services of the Kernel. Question: What is the difference between VIRTUAL MACHINE and VIRTUAL MEMORY?

Answer: A virtual machine is actually a software that gives you the functionality of a complete machine. Means that you can install complete Os inside a virtual machine. VMWare is ad famous virtual machine. Virtual memory is a memory management technique that you will study in coming lectures. It is pre-mature to explain virtual memory here in detail. Question: ~/courses/cs604. In this path what ~ represent? Please explain

Answer: ~ is used to represent HOME directory Question: Which software will be used during this course ?

Answer: Insha Allah we will be using Linux Operating System in this course. So you need to install this OS as soon as possible as you will be given assignments that you will have to do in C language using Linux environment. Question: In DOS if we want to enter into a directory we write "cd dirName" and same is the case in Linux. In MSDOS if we want to go to the beginning of the current drive then we type "cd\". In Linux we just type "cd" to go to the home directory. In DOS we can go to the parent directory of the current directory by type command "cd.." but please, inform that how can we go to the parent directory of the current directory in Linux.

Answer: You can come back to the home directory by cd ~ command. Question: Explain significant difference between process & program.

Answer: We usually say that a program in execution is called a process. Program is actually sequence of well defined code instructions. explain significant difference between process & program. Question: Where do I practice the Linuxands such as ls, mkdir etc.

Answer: Open the Terminal and practice these commands at its prompt. Question: Where do I practice the Linuxands such as ls, mkdir etc.

Answer: Open the Terminal and practice these commands at its prompt. Question: What are the contents of Swapper directory in Unix tree hierarchy?

Answer: Swap space is a temporary memory location. Swap space is used when physical memory is not sufficient to hold all the running processes. If the system needs more memory resources and the physical memory is full, inactive pages in memory are moved to the swap space. So usually swap space holds the contents of the man memory temporarily. Question: When a process is doing IO, even then CPU is doing all the work i.e CPU has to execute the instructions for IO . So how we differentiate between IO bound and CPU bound process?

Answer: Actually, while working on the computer, we get the feeling that I/O operations as well as CPU operations are running in parallel. We get this feeling because of excellent processor and time sharing algorithms. Otherwise a single CPU can do only I/O burst or CPU burst at a given time. Question: At the end of lecture 6, in the last few minutes the professor says that after the fork() system call the parent and the child share the following: • Environment • Open file descriptor table • Signal handling settings • Nice value • Current working directory • Root directory • File mode creation mask (umask) The professor says that the Open file descriptor will be explained later but he did not say anything about the Nice Value and File Mode creation mask. Please explain the Nice Value and File Mode creation mask in the context of fork() system call.

Answer: Nice value is a number that influence the property of the process. If the nice value is high, it makes the process to run at lower priority and if the value of nice is lower, the process runs at higher priority. The file mode creation mask (often called the umask) determines the default permissions for any file created by the process. For example, a file created by the create command has the permissions specified by the umask unless the create command specifies explicit (Ref:

Question: Last few lines of the handouts of lecture 6 say that " Child has its own copy of parent’s file descriptors." What does it mean? Please explain

Answer: It means that the file descriptor of the child is different from that of the parent and child maintain its own file descriptor. Question: In Unix/Linux process tree, each does each process corresponds to a directory? Suppose I am in /home/aamir directory; and here I create an other directory test ie "mkdir /home/aamir test", does it mean a new process named "test " is created?

Answer: If you create a directory or a file then the process of creation of that directory or file could be termed as a process while directory 'test' is not a process itself. Question: What is difference between a logical and physical resource, could you please give one example of each?

Answer: Example of Physical resource is I/O devices, CPU etc. Whereas example of Logical resource are processes, shared memory or variables.