1.5 COMPUTER LANGUAGES

1.5 COMPUTER LANGUAGES

Programming Language

Def:

            A set of instructions given to the computer to execute a particular task is called a program and the language in which we write a program is called the programming language.

Computer programming languages are classified into three categories:

Ø  High-level Language

Ø  Middle-level Language

Ø  Low-level Language

 

Fig 31: Computer Programming Languages

 

1.      Low-level Language

·         Low-level language is easily understood by computers.

·         They are machine dependent.

·         Programmes written in these languages are not transferable from one computer to another.

 

a.      Machine Language

·   It belongs to first generation of computer languages.

·   The vocabulary of this language consists of two binary numbers 0’s and 1’s where 0 indicates low voltage and 1 indicates high voltage.

·   Each instruction has a specific format, consisting of two fields. The first field is opcode and the second field is address.

 

OPCODE

ADDRESS

where

OPCODE à Stands for operation code. It indicates what operation is to be done, like addition, subtraction, load, store, etc.

ADDRESS à Memory location where data is referenced.

Advantages

                                                                                i.            Can be directly typed and executed

                                                                              ii.            No translator program is required.

Disadvantages

                                                                                i.            Difficult to remember machine instructions.

                                                                              ii.            Difficult to understand, modify and debug

                                                                            iii.            Difficult to remember addresses of data and instructions.

                                                                            iv.            Each and every information is numerical in nature.

Program to add two numbers in machine language

PROGRAM	EXPLANATION
0011 1100	Load A register with value 7
0000 0111
0000 0110	Load B register with 10
0000 1010
1000 0000	A ß A + B
0011 1010	Store the result into the memory location whose address is 100
0110 0110
0111 0110	Halt processing

 

b.      Assembly Language

·   It belongs to second generation of computer languages.

·   In this language we make use of symbolic words referred as mnemonics.

·   The program which translates assembly language program into machine language program is called assembler.

                                                       Fig 32: Translation by Assembler

Advantages

                                                                                i.            Easy to remember operation codes.

                                                                              ii.            Easy to understand the program.

                                                                            iii.            Easy to write program, modify and debug.

                                                                            iv.            Need not remember addresses of operands and instructions locations.

Disadvantages

                                                                                i.            The mnemonics are machine dependent. They differ from one computer to another.

                                                                              ii.            There is no standardization.

                                                                            iii.            It has less efficient than machine language.

 

Program to add two numbers in assembly language

PROGRAM	EXPLANATION
LD A, 7	Load A register with value 7
LD B, 10	Load B register with 10
ADD A, B	A ß A + B
LD (100), A	Store the result into the memory location whose address is 100
HALT	Halt processing

 

2.      Middle-level Language

·         The “C” language is called middle-level language because it has the features of both high-level language and low-level language.

3.      High-level Language

·         High-level language is easily understood by the user.

·         These languages are more concerned with the problem specification and not oriented towards the details of a hardware.

·         HLL are English-like statements.

·         The elements of these languages are alphabets, digits, punctuations and other special symbols.

·         Program written for one computer can be run on another computer with very little or no modification.

·         In high-level languages, we have two types of translators – compiler and interpreter.

 

                                                Fig 33: Translation by Compiler / Interpreter

 

Difference between Compiler and Interpreter

S.NO.	COMPILER	INTERPRETER
1.	Scans the entire program before translating it into machine code.	Translates and executes the program line by line.
2.	Converts the entire program to machine code and only when all the syntax errors are removed, does execution takes place.	Each time the program is executed, every line is checked for syntax error and then converted to the equivalent machine code.
3.	Slow in debugging.	Good for debugging.
4.	Execution time is less.	Execution time is more.
5.	Memory requirement is more.	Memory requirement is less.
Ex:	C, C++, JAVA	BASIC, JAVA, LISP

 

                                    Advantages

                                                                                i.            Easy to understand.

                                                                              ii.            Easy to write, modify and debug.

                                                                            iii.            Standardized.

                                                                            iv.            Portability.

Disadvantages

                                                                                i.            Less efficient than low-level language.

                                                                              ii.            Poor control on hardware.

a.      Procedural Language

·         Procedural language is a type of computer programming language that specifies a series of well-structured steps and procedures within its programming context to compose a program. It contains a systematic order of statements, functions and commands to complete a computational task or program.

·         Procedural language segregates a program within variables, functions, statements and conditional operators. Procedures or functions are implemented on the data and variables to perform a task. These procedures can be called/invoked anywhere between the program hierarchy, and by other procedures as well.

·         Example: C++, JAVA, PASCAL, FORTRAN
 

b.      Non-procedural Language

·   A computer language that does not require writing traditional programming logic. Also known as a "declarative language," users concentrate on defining the input and output rather than the program steps required in a procedural programming language.

·   Example: Prolog, LISP

c.       Problem-oriented Language

·   Problem-oriented Languages were designed to solve specific problems e.g. querying databases and allowed the programmer to concentrate more on the problem rather than spending time learning the complex syntax of the language.

·   Example: MATLAB

Difference between Machine Language and High-level Language

S.NO.	MACHINE LANGUAGE	HIGH-LEVEL LANGUAGE
1.	Uses only two symbols 0’s and 1’s.	Uses alphabets, digits and special symbols.
2.	Each instruction is a sequence of 0’s and 1’s.	Each instruction is like English statement.
3.	Can be directly executed.	Cannot be directly executed.
4.	Machine dependent.	Machine independent.
5.	Difficult to understand, modify and debug.	Easy to understand, modify and debug.
6.	Efficient (fast)	Less efficient (slow)
7.	No standardization followed.	Standardization.

 

Difference between Assembly Language and High-level Language

S.NO.	ASSEMBLY LANGUAGE	HIGH-LEVEL LANGUAGE
1.	Mnemonic instructions.	English-like instructions.
2.	Machine dependent.	Machine independent.
3.	Assembler is used in translation process.	Compiler or interpreter is used in translation process.
4.	Difficult to understand, modify and debug.	Easy to understand, modify and debug.

 

Concept of Linker and Loader

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.

Not only built in libraries, it also links the user defined functions to the user defined libraries. Usually a longer program is divided into smaller subprograms called modules. And these modules must be combined to execute the program. The process of combining the modules is done by the linker.

 

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. 

Translation Hierarchy

Fig 34: Translation Hierarchy