Operating System Concept

WEEK 2-3: COMPUTER SYSTEM SOFTWARE

·          Operating System Concept

An operating system (OS): Is a collection of software that manages computer hardware resources and provides common services for computer programs.

The operating system is an essential component of the system software in a computer system and is the first program loaded into the computer by a boot program and remains in memory at all times.

Application programs usually require an operating system to function.

For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware.

Operating systems can be found on almost any device that contains a computer from cellular phones and video game consoles to supercomputers and web servers.

Examples of popular modern operating systems include Android, BSD, iOS, Linux, OS X, QNX, Microsoft Windows, Windows Phone, and IBM z/OS.

All these, except Windows, Windows Phone and z/OS, share roots in UNIX.

—  Types of operating systems

Within the broad family of operating systems, there are generally four types, categorized based on the types of computers they control and the sort of applications they support. The categories are:

a)       Real-time operating system

b)       Single-user, single task

c)        Single-user, multi-tasking

d)       Multi-user 

A.     REAL-TIME OPERATING SYSTEM(RTOS)

v  Real-time operating systems are used to control machinery, scientific instruments and industrial systems.

v  An RTOS typically has very little user-interface capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use.

v  A very important part of an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time, every time it occurs.

v  In a complex machine, having a part move more quickly just because system resources are available may be just as catastrophic as having it not move at all because the system is busy.

B.      SINGLE-USER, SINGLE TASK

v  As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time.

v  The Palm OS for Palm handheld computers is a good example of a modern single-user, single-task operating system.

C.      SINGLE-USER, MULTI-TASKING

v  This is the type of operating system that allows a single user to have more than one task/job/process/program running at the same time.

v  This is the type of operating system most people use on their desktop and laptop computers today.

v  Microsoft's Windows and Apple's MacOS platforms are both examples of operating systems that will let a single user have several programs in operation at the same time.

v  For example, it's entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the Internet while printing the text while listening music

D.     MULTI-USER

v  A multi-user operating system allows many different users to take advantage of the computer's resources simultaneously.

v  The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users.

v  Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.

—  Utilities Software

Is a system software designed to help analyze, configure, optimize, or maintain a computer.

—  Compiler, Interpreter, Linker, Loader

COMPILER

 It is a program which translates a high level language program into a machine language program. A compiler is more intelligent than an assembler. It checks all kinds of limits, ranges, errors etc. But its program run time is more and occupies a larger part of the memory. It has slow speed. Because a compiler goes through the entire program and then translates the entire program into machine codes. If a compiler runs on a computer and produces the machine codes for the same computer then it is known as a self compiler or resident compiler. On the other hand, if a compiler runs on a computer and produces the machine codes for other computer then it is known as a cross compiler.

INTERPRETER: 

An interpreter is a program which translates statements of a program into machine code. It translates only one statement of the program at a time. It reads only one statement of program, translates it and executes it. Then it reads the next statement of the program again translates it and executes it. In this way it proceeds further till all the statements are translated and executed. On the other hand, a compiler goes through the entire program and then translates the entire program into machine codes. A compiler is 5 to 25 times faster than an interpreter.

By the compiler, the machine codes are saved permanently for future reference. On the other hand, the machine codes produced by interpreter are not saved. An interpreter is a small program as compared to compiler. It occupies less memory space, so it can be used in a smaller system which has limited memory space.

LINKER

Linker: In high level languages, some built in header files or libraries are stored. These libraries are predefined and these contain basic functions which are essential for executing the program. These functions are linked to the libraries by a program called Linker. If linker does not find a library of a function then it informs to compiler and then compiler generates an error. The compiler automatically invokes the linker as the last step in compiling a program.

LOADER

Loader is a program that loads machine codes of a program into the system memory.

In Computing, a loader is the part of an Operating System that is responsible for loading programs. It is one of the essential stages in the process of starting a program. Because it places programs into memory and prepares them for execution. Loading a program involves reading the contents of executable file into memory.  Once loading is complete, the operating system starts the program by passing control to the loaded program code. All operating systems that support program loading have loaders. In many operating systems the loader is permanently resident in memory.

—  Functions of operating system

At the simplest level, an operating system does two things:

v  It manages the hardware and software resources of the system. In a desktop computer, these resources include such things as the processor, memory, disk space and more (On a cell phone, they include the keypad, the screen, the address book, the phone dialer, the battery and the network connection).

v  It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware.

The operating system's tasks, in the most general sense, fall into six categories:

a)       Processor management

b)       Memory management

c)        Device management

d)       Storage management (Retrieves and manipulates files)

e)        Application interface (Running the applications)

f)         User interface

—  DOS operation

Disk Operating System (DOS)

Before knowing the operations of DOS, we must know what DOS is. DOS stands for disk operating system. The term DOS can refer to any operating system, but
it is most often used as a shorthand for MS-DOS (Microsoft disk operating system). Originally developed by Microsoft for IBM, MS-DOS was the standard operating system for IBM-compatible personal computers.

DOS uses a command line, or text-based interface, that allows the user to type commands. By typing simple instructions such as pwd (print working directory) and cd (change directory), the user can browse the files on the hard drive, open files, and run programs. While the commands are simple to type, the user must know the basic commands in order to use DOS effectively (similar to Unix). This made the operating system difficult for novices to use, which is why Microsoft later bundled the graphic-based Windows operating system with DOS.

Here are some basic functions of DOS;

• Navigation - One of the aspects of MS-DOS that still survives in Windows is the drive and directory system. The OS uses letters to identify drives, and directories and sub-directories with eight-character names denoted by a backslash character. “C:\GAMES” represents one level down from root, while “C:\GAMES\CARDS” is one further sub-directory level down. You can move through these directory levels using the CD or “change directory” command, using “CD ..” to return to a higher level. The “mkdir” or MD command creates directories, while the “rmdir” or RD command deletes them. Since most tasks in MS-DOS take place in the current sub-directory, navigation is an important function of the operating system.
• File Manipulation - Files in MS-DOS use an “8.3” naming system, eight characters for the file name and three characters for an identifying suffix that tells the operating system what type of file it is. Wildcards are available for file manipulation, with “?” representing a single character and “*” representing any number of characters. For instance, the command “COPY *.* C:\GAMES” will copy all files in the current directory into the C:\GAMES directory. To move files from one folder to another in early versions of DOS, you would first copy them into the target directory and then delete the originals, as the "Move" command did not exist until DOS 6.0
• Running Programs - Running programs under MS-DOS simply requires you to enter the eight-character name of the program, if the file is a type that the operating system understands as an executable. Files with the .exe and .com suffixes are binary executable, while .bat files are text scripts that can trigger multiple programs in succession. These programs often allow you to perform more complex operations than MS-DOS would allow, as well as take advantage of more installed memory. Early versions of Windows required you to boot into MS-DOS and run WIN.EXE to load the graphic user interface
• Drive Utilities - MS-DOS also contains a number of utilities for disk and drive management. If a drive begins began showing symptoms of structural problems, the CHKDSK or “checkdisk” command scans for errors and, if possible, corrects them. The FDISK command allows you to “low-level format” a drive, altering its partition structure, while FORMAT wipes any disk and prepares it for re-use. In modern Windows operating systems, however, a set of more user-friendly tools replace these functions, helping prevent accidental data loss.

Below is a listing of 10 Most common (Good to know) DOS Commands based on my usage:

• Ping - Ping is my favorite command of all. I use it to check my internet connection when I find difficulty in connecting to the internet. What ping does is simple. It pings a website from your computer, i.e. this command sends a packet of data to a destination site and it is returned back to you, thus proving that you have established a connection.
• Ipconfig - This is a powerful MS-DOS command to view your network status and also perform operations on the same.
• Chkdsk - Chkdsk stands for ‘check disk’. It checks your disks drives and finds errors. You can also repair your affected disk drives with this command using the “/f “ options, which will fix your drive.
• TraceRT - This command will trace the path of packets to a particular server of a website or IP
• Netstat - This is another network command, unofficially short term for network statistics. It lists the status of your network, the number of active connections and open ports in your system currently along with their current states.
• Help - The help command all the available commands that you can use in the MS-DOS prompt. You can try out the various commands in that list, but make sure you know what you are doing
• Format - Formatting a drive is quite easy with the ‘Format’ MS-DOS command. You can try this command when you have a defective USB flash drive or when you need to format a particular drive on your computer.
• Dir - This command will list the contents of the current directory you are in. It takes a lot of parameters like /t and /p which will list the files according to a particular criteria.
• SystemInfo - This is one of my much loved and common dos command. It gives you a detailed description about your system components like processor, memory and much more. You can also use it to check whether your system is 32 bit or 64 bit.
• Taskkill - The taskkill command in MS-DOS kills or terminates a running process. It can become handy when some of your programs freeze or when they stop responding.

—  Virtualization of operating systems.

Operating system virtualization is a technology that involves tailoring a standard operating system so that it can run different applications handled by multiple users on a single computer at a time.    

OR

Operating system virtualization is the use of software to allow a piece of hardware to run multiple operating system images at the same time.

The operating systems do not interfere with each other even though they are on the same computer.

In OS virtualization, the operating system is untouched so that it operates like several different, individual systems. The virtualized environment accepts commands from different users running different applications on the same machine. The users and their requests are handled separately by the virtualized operating system.