COURSE TITLE: FOUNDATIONS OF SEQUENTIAL PROGRAM
CODE: CSC 206
TOPIC TWO
Machine language, assembly language and assemblers, low/high level languages (Machine-level implementation of high-level language)
Objectives
By the end of this class, students should be able to:
1. describe computer/programming language
2. list and describe the three different types or levels of programming languages
3. list the advantages of programming languages
4. list the disadvantages of programming languages
5. list and describe the different examples of types or levels of programming languages
DISCLAIMER
The contents of this document are intended for leaning purposes at the undergraduate level. The materials are from different sources including the internet and the contributors do not in any way claim authorship or ownership of them.
COMPUTER / PROGRAMMING LANGUAGES
Computer or Programming Languages are sets of words, symbols and codes used to write programs. Different programming languages are available for writing different types of programs. Some languages are specially used for writing business programming, others are used for writing scientific program etc.
There are three types or levels of computer programming:
1. Machine language
2. Low level Languages
3. High Level Languages
Machine language
Machine Language is the actual bits used to control the processor in the computer, usually viewed as a sequence of hexadecimal numbers (typically bytes). The processor reads these bits in from program memory, and the bits represent "instructions" as to what to do next. Thus machine language provides a way of entering instructions into a computer (whether through switches, punched tape, or a binary file).
Machine Language instruction has two (2) parts. The first part is the operation code which tells the computer what function to perform and the second part is the operand which tells the computer where to find or store the data which is to be manipulated. A programmer needs to write numeric codes for the instruction and storage location of data.
Characteristics of Machine Language:
1. It is the first generation programing language
2. It is much difficult than Assembly Language
3. Difficult to understand by the human
4. It is in the form of 0s and 1s
5. Machine Language varies from platform
6. It cannot be changed easily
7. It does not support modification
8. The risk of existence of error is high 9. The binary code cannot be memorized
10. No need of compiler
Disadvantages of Machine Language
1. It is machine dependent, that is, it differs from computer to computer
2. It is difficult to program and write
3. It is prone to errors
4. It is difficult to modify.
Low Level Languages
A low-level programming language is a programming language that provides little or no abstraction from a computer's instruction set architecture—commands or functions in the language map closely to processor instructions. The word "low" refers to the small or nonexistent amount of abstraction between the language and machine language; because of this, low-level languages are sometimes described as being "close to the hardware".
Low level programming languages are languages that will let you have direct access on the machine resources (CPU Registers, Memory, I/O ports, etc)
Examples of Low Level Languages are:
1. Assembly Language
2. C (By comparing it to Assembly, It’s high level language but contains low level features, so by many programmers it’s called portable assembly, and by comparing it to scripting languages, it’s low level language)
3. We can add other languages that are similar to C or support low level features provided by C, like C++, but remember that C++ comes with more high level features than C like Object-Oriented, Better standard library, Templates, etc
So it depends not only on the language, but how we are using it. Some programs written in C, don’t use the low level features, these programs looks like it was written in high-level language, because in C we have the language constructs that help in Abstraction too!
Assembly Language
Assembly (or assembler) language, often abbreviated as asm is a more human readable view of machine language. Instead of representing the machine language as numbers, the instructions and registers are given names (typically abbreviated words, or mnemonics, eg ld means "load", ADD means addition, SUB means subtraction etc). Unlike a high level language, assembly language is very close to the machine language that is why it is also called symbolic machine code. The main abstractions (apart from the mnemonics) are the use of labels instead of fixed memory addresses, and comments. Each assembly language is specific to a particular computer architecture.
Example: instead of using “1100 000”, we write the symbol ADD to mean the same thing(addition)
Assembler.
Assembler is an example of computer utility program which converts or translates assembly language into executable machine. It assembles the machine language program in the main memory of the computer and makes it ready for execution.
The conversion process is referred to as assembly, or assembling the source code. Assembly time is the computational step where an assembler is run.
A disassembler performs the reverse function (although the comments and the names of labels will have been discarded in the assembler process).
Characteristics of Assembly Language:
1. It is a second generation programming language
2. It is less difficult than machine language 3. Easy to understand by the human
4. It uses symbolic instructions, descriptive names for data items and memory location
5. The Assembly Language is platform dependent
6. It is easily Modifiable
7. The risk of occurrence of error is reduced
8. Memorability is high
9. It needed a compiler to run which is known as assembler
10. One instruction per line.
11. Labels provide names for addresses (usually in first column).
12. Instructions often start in later columns.
13. Columns run to end of line.
Advantages of Assembly Language
1. It is easy to understand and use
2. It is easy to locate and correct errors
3. It is easier to modify
4. Speed - Assembly language programs are generally the fastest programs around.
- Machine language created by compilers are usually longer and this makes them slower.
5. Space - Assembly language programs are often the smallest.
6. Capability - You can do things in assembly which are difficult or impossible in HLLs. - Applications requiring access to low level machine capability are often written in assembly language, example device drivers.
7. Knowledge
- Your knowledge of assembly language will help you write better programs, even when using HLLs.
- Assembly language requires learning the architecture of the specific machine on which assembly language is used
Disadvantages of Assembly Language
It is also a machine dependent language
High Level Languages
High Level Languages are the types of computer programming languages close to human languages, they are combinations of English language-like instructions such as input, print etc and mathematical symbols. A program written in HLL are easier to write and modify.
Each statement in a HLL is a micro instruction which is translated into several machine language instructions.
A compiler is a translator program which translates a HLL programming language into equivalent machine language programs. It compiles a set of machine language instructions for every HLL program.
HLL are further divided into the following categories:
1. Procedural Languages
2. Object Oriented Languages
3. Non-Procedural Languages 1. Procedural Programming languages Procedural programming are also known as third generation language of 3G. in these language, program is a predefined set of instructions. Computer executes these instructions in the same sequence in which the instructions are written. Each instruction in this language tells the computer what to do and how to do it. Some popular PL are: FORTRAN, BASIC, COBOL, PASCAL, C etc
2. Object Oriented Programming
OOP is a technique in which programs are written on the basis of object. An object is a collection of data and functions. Objects may represent a person, thing or place in real world, in OOP, data and all possible functions on data are grouped together. Object Oriented programs are easier to learn and modify. C++ and Java are popular Object Oriented Language.
Characteristics of OOP
The following are the characteristics of OOP:
1. Object
2. Classes
3. Real world modeling
4. Reusability: through the use of inheritance
5. Information hiding- using encapsulation function
6. Polymorphism
3. Non-Procedural Language
NPL are also known as fourth generation language or 4GL. In NPL, user only needs to tell the computer “what to do” not “How to do it”. An important advantage of NPL is that they can be used by NP user to perform a specific task. These languages accelerates program process and reduce coding errors. 4GL are normally used in database application and report generation. Some important non-procedural languages are as follows:
1. SQL (Sequential Query Language) e.g MySQL
2. RPG (Report Program Generator) e.g Crystal Report
Advantages of High-Level Languages
1. They are machine independent
2. They are easier to learn and use
3. They are easier to read and write
4. They are easier to maintain and gives few errors.
Execution modes
There are three general modes of execution for modern high-level languages:
Interpreted
When code written in a language is interpreted, its syntax is read and then executed directly, with no compilation stage. A program called an interpreter reads each program statement, following the program flow, then decides what to do, and does it. A hybrid of an interpreter and a compiler will compile the statement into machine code and execute that; the machine code is then discarded, to be interpreted anew if the line is executed again. Interpreters are commonly the simplest implementations of the behavior of a language, compared to the other two variants.
Compiled
When code written in a language is compiled, its syntax is transformed into an executable form before running. There are two types of compilation:
Machine code generation Some compilers compile source code directly into machine code. This is the original mode of compilation, and languages that are directly and completely transformed to machine-native code in this way may be called "truly compiled" languages.
Source-to-Source Translated or Trans-compiled
Code written in a language may be translated into terms of a lower-level programming language for which native code compilers are already widely available. JavaScript and the C programming language are common targets for such translators.
Note that languages are not strictly "interpreted" languages or "compiled" languages. Rather, implementations of language behavior use interpretation or compilation. For example, Algol 60 and Fortran have both been interpreted (even though they were more typically compiled).
High-level language computer architecture
Alternatively, it is possible for a high-level language to be directly implemented by a computer – the computer directly executes the HLL code. This is known as a high-level language computer architecture – the computer architecture itself is designed to be targeted by a specific high-level language.
Assignment
1. List the differences between Assembly language and Machine Language
2. List the differences between HLLs and Low LLs.
3. Draw a diagram of how computer translates(using translator) a source code
4. Draw a diagram of how computer compiles(using compiler) a source code