Page 462 - DCAP103_Principle of operating system

Unit 14: Case Study of Linux Operating System

14.9 Keywords Notes

Kernel: The Linux kernel is an operating system where kernel used by the Linux family of Unix-
like operating systems. It is one of the most prominent examples of free and open source software.
Memory: The term memory identifies data storage that comes in the form of chips, and the word
storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually
used as shorthand for physical memory, which refers to the actual chips capable of holding data.
Some computers also use virtual memory, which expands physical memory onto a hard disk.

MINIX : MINIX is a new open-source operating system designed to be highly reliable, flexible,
and secure. It is loosely based somewhat on previous versions of MINIX, but is fundamentally
different in many key ways.
Page Allocator: An allocation scheme which combines a normal power of two allocator with
free buffer coalescing and the basic concept behind it is quite simple. Memory is broken up into
a large blocks of pages where each block is a power of two numbers of pages.
Paging: The operating system copies a certain number of pages from your storage device to
main memory. When a program needs a page that is not in main memory, the operating system
copies the required page into memory and copies another page back to the disk. One says
that the operating system pages the data. Each time a page is needed that is not currently in
memory, a page fault occurs. An invalid page fault occurs when the address of the page being
requested is invalid.
System Call: Operating systems contain sets of routines for performing various low-level
operations. For example, all operating systems have a routine for creating a directory. If you
want to execute an operating system routine from a program, you must make a system call.
Threads: A thread is placeholder information associated with a single use of a program that can
handle multiple concurrent users.
UNIX: Unix is a multitasking, multiuser computer operating system, is originally developed
in 1969 by a group of AT&T employees at Bell Labs.

14.10 Review Questions

1. Can a page fault ever lead to the faulting process being terminated? If so, give an example.
If not, why not?

2. Why are open file description tables necessary in Linux?
3. A non-real time Linux process has priority levels from 100 to 139. What is the default
static priority and how is the nice values used to change this?
4. Why do you think the designers of Linux made it impossible for a process to send a signal
to a another process that is not in its process group?

5. In every process’ entry is the task structure, the PID of the process’ parent is stored. Why?
6. When a new process is forked off, it must be assigned a unique integer as its PID. Is it
sufficient to have a counter in the kernel that is incremented on each process creation,
with the counter used as the new PID? Discuss your answer.

Answers to Self Assessment
1. (a) 2. (b) 3. control 4. window manager
5. Magic characters 6. fsck 7. text segement

8. pinned 9. block special file 10. Superblock

LOVELY PROFESSIONAL UNIVERSITY 455