1. Operating System Interface between a user and the computer hardware
Provides an environment in which a user can
execute programs
Goals
Make the computer system convenient to use
Use the computer hardware (resources) in an efficient manner

2. Functions of Operating System
Program Creation --- editors, debuggers, ... etc.. These are in the forms of utility programs that are not actually part of the O.S. but are accessible through the O.S.
Program Execution --- to execute a program, instructions and data must be loaded into the main memory, I/O devices and files must be initialized.
Access to I/O devices --- as if simple read and write to the programmers
Controlled Access to Files --- not only the control of I/O devices, but file format on the storage medium.

3. Functions of Operating System(Contd…)
System Access --- shared and public resources, protection of resources and data, resolve conflicts in the contention for resources.
Error Detection and Response
Internal/external hardware errors (memory error, device failures and mal-functions)
Software errors (arithmetic overflows, attempt to access forbidden memory locations, inability of the O.S. to grant the request of an application)
Ending a program, retrying , and reporting errors.
Accounting --- collect usage statistics for various resources, billing, and monitoring performance.

4. Generation of Languages

5. Programming languages
A set of rules ,symbols and characters that allows the user to communicate with the computer.
Programming Language
Machine Language
Assembly Language
High-level Language

6. Machine Language Fundamental language of a computer.
Set of instruction codes(binary or decimal) which can be directly understood by the computer is called machine language.
String of binary digits(1’s or 0’s).
An instruction has two-part format: opcode and operand.
OPCODE
OPERAND
What function to perform
Where to find the data

7. Advantages limitations
Fast because machine instructions are understood directly without any translation.
limitations
Error prone
Difficult to modify
Machine dependent
Difficult to program

8. Assembly Language
Language that allows instructions and storage locations to be represented by letters and symbols instead of numbers.
Also known as symbolic language.
Example: Program to add 2 numbers
CLA A
ADD B
STORE C
TYPE C
HALT

9. One-to-one correspondence
Assembler
Assembler is a translator program that translates an assembly program into its equivalent machine language program.
System software supplied by computer manufacturers.
Input
Output
Assembler
Machine language program
One-to-one correspondence
Source Program
Object
Program

10. Advantages over Machine Language
Easier to understand and use.
Easy to locate and correct errors
Easier to modify
No worry about addresses
Efficiency of machine language
Limitations
Machine dependent
Knowledge of hardware required
Machine level coding

11. High Level Languages
Language that uses English words and/or mathematical symbols rather than the mnemonic codes.
Overcome the limitations of low level languages.
E.g. a statement to add to numbers A and B using C language is
sum=A+B;
Some common high level languages are
FORTRAN
COBOL
BASIC
C AND C++
JAVA

12. Compiler
A translator program that translates a high level language into its equivalent machine language program.
Can translate only those programs that have been written in the language for which the compiler is meant.
Input
High level language program
Output
Compiler
Machine language program
One-to-many correspondence
Source Program
Object
Program

13. High level language program
Interpreter
Translator program that translates a high level language program into its equivalent machine language program.
Translates and executes a high level language program statement- by statement.
Does not generate any object code of the source program.
High level language program
Input
Output
Interpreter
Result of program execution
(Source Program)

14. Advantages limitations Lower efficiency Less flexibility
Machine independence
Easier to learn and use
Fewer errors
Lower program preparation cost
Better documentation
Easier to maintain
limitations
Lower efficiency
Less flexibility

15. Fourth Generation Languages
Fourth-generation languages are programming languages closer to human languages than typical high-level programming languages.
It allows the user to simply specify what to do without describing how to do.
All 4GLs are designed to reduce programming effort, the time it takes to develop software, and the cost of software development.
Some common 4GL’s are Oracle, SQL etc.