Csc 112 – lecture one

An operating system, or "OS" for short, is software that communicates with the hardware and allows other programs to run. The operating system is considered the most important program that is on a computer. The operating system basically runs the computer and allows other programs to run as well.

It comprises the fundamental files your computer needs to boot up and function.

Every desktop computer, tablet, and smartphone includes an operating system that provides basic functionality for the device.

Common desktop operating systems include Windows, Mac OS X, and Linux.

While Windows and Linux can be installed on standard PC hardware, Mac OS X can only run on Macintosh computers. Therefore, the hardware you choose affects what operating system(s) you can run.

Mobile devices, such as tablets and smartphones also include operating systems that provide a GUI and can run applications. Common mobile OSes include Android, iOS, and Windows Phone. These OSes are developed specifically for portable devices and therefore are designed around touchscreen input. While early mobile operating systems lacked many features found in desktop OSes, they now include advanced capabilities, such as the ability to run third-party apps and run multiple apps at once.

The operating system is the most important program that runs on a computer.

Every general-purpose computer must have an operating system to run other

programs. Operating systems perform basic tasks, such as recognizing input

from the keyboard, sending output to the display screen, keeping track of files

and directories on the disk, and controlling peripheral devices such as disk

drives and printers.

For large systems, the operating system has even greater responsibilities

and powers. It makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Since the operating system serves as a computer's fundamental user interface, it significantly affects how you interact with the device. Therefore, many users prefer to use a specific operating system. For example, one user may prefer to use a computer with Mac OS X instead of a Windows-based PC.

Another user may prefer an Android-based smartphone instead of an iPhone, which runs the iOS.

When software developers create applications, they must be write and compile them for a specific operating system. This is because each OS communicates with the hardware differently and has a specific application program interface, or API, that the programmer must use. While many popular programs are crossplatform, meaning they have been developed for multiple OSes, some are only available for a single operating system. Therefore, when choosing a computer, it is important to make sure the operating system supports the programs you want to run.

Not all computers have operating systems. For instance, the microwave oven (it is a computer) in the kitchen does not need an operating system.

It has a set of tasks to perform, very straightforward input to expect (a numbered input pad and a few pre-set buttons) and simple, unchanging hardware to control.

For a computer like this, an operating system would be unnecessary load, causing the development and manufacturing costs to increase unnecessarily and adding complexity where none is required. Instead of having an OS, the computer in a microwave oven simply runs a single hard-wired program all the time. However, all desktop computers have operating systems.

Common families of OSes are:

1. 
   GNU/Linux
   

1. 
   Debian (derivatives include Ubuntu, Mint, Trisquel)
   
2. 
   Red Hat (derivatives include Fedora, Blag)
   
3. 
   Arch (derivatives include Parabola)
   
4. 
   Gentoo (derivatives include Ututo XS)
   
5. 
   Slackware
   

2. 
   BSD
   

1. 
   FreeBSD
   
2. 
   Mac OS X
   
3. 
   OpenBSD
   
4. 
   NetBSD
   

3. 
   Microsoft Windows
   

1. 
   Windows XP
   
2. 
   Windows Vista
   
3. 
   Windows 7
   
4. 
   Windows 8
   

4. 
   iOS
   

1. 
   iOS 4
   
2. 
   iOS 5
   
3. 
   iOS 6
   

5. 
   Android
   

1. 
   CyanogenMod
   
2. 
   Replicant
   

The following are the importance of an OS:

1. 
   The OS helps devices to serve a variety of purposes, performing several different tasks.
   
2. 
   It helps devices to interact with users in more complicated ways.
   
3. 
   It ensures the device keeps up with needs that change over time. In any device that has an operating system, there's usually a way to make changes to how the device works without totally discarding the device. Updates can be made to the software running on the device and the operating system can be changed.
   
4. 
   It enables startup application programs to run.
   
5. 
   It ensures the allocation of resources needed to execute programs and this is done by identifying: the programs that are running, the need for memory, peripheral devices and data protection requirements.
   
6. 
   It provides facilities for data compression, sorting, mixing, cataloging and maintenance of libraries, through utility programs available.
   

1. 
   kernel and drivers
   
2. 
   computer programs and software
   

1. 
   Batch Processing System
   

2. 
   Real-time Systems
   

3. 
   Single User Operating System
   

4. 
   Multi-Tasking Operating System
   

5. 
   Multi-User Operating System
   

6. 
   Distributed Operating System
   

Programming languages are artificial languages designed to control computers and many man hours have been spent to develop new and improved languages. There are thousands of different programming languages, but most conform to a few basic paradigms.

A computer programming language is a vocabulary and set of grammatical rules for instructing a computer to perform specific tasks.

The term “programming language” usually refers to high-level languages, such as BASIC, C, C++, COBOL, FORTRAN, Ada, and Pascal. Each language has a unique set of keywords (words that it understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more complex than the languages the computer actually understands, called machine languages. Each different type of CPU has its own unique machine language.

A simple way to understand programming languages is to think of them as bricks which can be used to create applications and operating system.  Generally Java is used for internet applications. C++ is a language of professional developers and used extensively in developing operating systems. PHP is another language used for internet applications. There is a new class of languages which are being utilized for the mobiles. These are light weight, modular languages which are used to design mobile applications.

Types of programming languages

There are three (3) basic types of computer programming languages. They are:

1. 
   Machine language
   
2. 
   Assembly language and
   
3. 
   High-level language.
   

Machine language is the only language that a computer understands. Each statement in a machine language program is a sequence of bits. Each bit may be set to 0 or 1. Series of bits represent instructions that a computer can understand. For example, the number 455 is represented by the bit sequence 111000111.

Machine language is a low-level programming language. It is easily understood by computers but difficult to read by people. This is why people use higher level programming languages. Programs written in high-level languages are compiled and/or interpreted into machine language so computers can execute them.
Assembly language

Assembly language is a representation of machine language. In other words, each assembly language instruction translates to a machine language instruction. The advantage of assembly language is that its instructions are readable. For example, assembly language statements like MOV and ADD are more recognizable than sequences of 0s and 1s. Though assembly language statements are readable, the statements are still low-level.

A disadvantage of assembly language is that it is not portable. In other words, assembly language programs are specific to a particular hardware. Assembly language programs for a Mac will not work on a PC. But this can be an advantage for programmers who are targeting a specific platform and need full control over the hardware.
High-level language

High-level languages are what most programmers use. Languages such as C, C++ and Java are all high-level languages. One advantage of high-level languages is that they are very readable. The statements in these languages are English-like. For example, you can gain a basic understanding of what a Java program is doing by simply reading the program source code. High-level languages use English words as statements. Loops in Java programs are indicated by the words for, while and do.

A disadvantage of high-level languages is that they are usually less powerful and less efficient. Since statements are high-level, you cannot code at the bit level the way you can with assembly language. High-level languages also need to be compiled and/or interpreted into machine language before execution.

Examples are Java, C#, Perl, Ruby, Python, PHP and JavaScript.

1. 
   First generation languages (abbreviated as 1GL)
   

2. 
   Second generation languages (2GL)
   

Generally, the 1GL and 2GL are low-level languages.

3. 
   Third generation languages (3GL)
   

4. 
   Fourth generation languages (4GL)
   

5. 
   Fifth generation languages (5GL)
   

As earlier discussed, a translator is a program which converts statements (program or instructions) written in one language to statements in another language especially to machine language.

There are three types of translators:

1. Assemblers

2. Compilers.

3. Interpreters.

This is a program, which translate assembly language into machine code. One machine instruction is generated for each source instruction. The resulting program can only be executed when the assembly process is completed. The assembler reserves space for the instructions and data, replaces mnemonic operating codes by machine codes and symbolic addresses by numeric addresses while it determines the machine representation of constants.

1. 
   It translates mnemonic operation codes, and symbolic addresses into machine addresses.
   
2. 
   Includes the necessary linkages for closed subroutines and insert appropriate machine code for macros.
   
3. 
   Allocates area of storage.
   
4. 
   Detects and indicates invalid source language instructions.
   
5. 
   Produces the object program on disk as required.
   
6. 
   Produces a printed listing of the source and object program with comments.
   

A compiler translates a high level language into machine language. The compiler translate the whole source program into machine code or object program prior to the object being loaded into main memory and execution. The resulting program can only be executed when compilation is completed.

1. 
   Translates the source program statements into machine code.
   
2. 
   Includes linkage for closed subroutines.
   
3. 
   Allocates areas of main storage.
   
4. 
   Generates the object program on cards, tapes or disc as required.
   
5. 
   Produces a printed copy of the source and object program when required.
   
6. 
   Tabulates list of errors found during program compilation. For example, the use of a word or statement not included in the language vocabulary, the rule of syntax or lexis.
   

Interpreter is more easily understood by comparing them with compiler. Both compilers and interpreters are commonly used for the translation of high-level language program but they perform the translation in two completely different ways. The difference between the compiler and the interpreter is in their translation process. For the compiler, the whole of the high level language source program is converted into machine code object program prior to the object program being loaded into main memory for execution. This in contrast to the interpreter which deals with the source program one instruction at a time, completely translating and executing each instruction before it goes onto the next.

Interpreters hardly produce object codes but call upon in-built routines instead. However, some intermediate codes are usually produced temporarily. The interpreter does not produce object program, it read source program, translates it and goes ahead to execute it.

The object program provided by a compiler fastens execution than any interpreter can do in the running of a program, the use of object program may however pose a problem where there is an error as it is very time consuming to discover the source of error, a compiler is capable of producing a machine code generated by it at any time, whereas an interpreter can only execute the source program. If a computer is used, the same program needs only to be translated once. Thereafter, the object program can be loaded directly into main storage and executed. However, when an interpreter is used, the source program will be translated every time the program is executed. Execution carried out in this way may be ten times slower than the execution of the equivalent object programs.

1. Handling user commands in an interactive system.

2. They debug programs as they run, that is, for each line of coding before implemented.

3. Handling software produced for or by different computer. In this case, the

interpreter may be essential if:

(a). Two dissimilar machines are to be connected together for operation, or