Course Overview

What are Computers?

• From Outside

– CPU box, Monitor, Keyboard, mouse and Printers

• From inside

– ICs, Chipsets, Hard Disks, PCB cards, Drives, Buses

– All the above are called Computer Hardware

– The physical engine that solves problems

Programmability

• Unique feature of Computers

• raw HW can not do anything on its own

• needs programs or software to do things

• Same hardware can be configured to do a variety of functions

• Programs provide this ability

• `run' or `execute' the program in the machine for this

What are Programs

• Sequence of precise instructions or commands

• tell the HW to read input,

• to compute simple arithmetic functions

• and to print outputs etc.

• Control HW to compute a variety of tasks

• It is the programs that provide the rich problem solving abilities

Programming Main focus of this course

Low-level Programming

• Programs that can run in a computer are low-level,

• Instructions are simple arithmetic and logical operation on binary numbers (sequences of 0 and 1)

• specific to the machine and will not run in other machines

• called as machine programs (assembly programs)

• very difficult to write and understand, error prone

• for most common applications not necessary

Example
mov R1,R2 – move the value from R1 to R2
add R2,R3,R4 – add R2 and R3 and store it in R4
sto R4, #010110 – store R4 in memory

High-level programming

• Instructions are complex operations on a variety of data objects

• programs are independent of machines

• closer to problem domain

• resembles natural language statements

• easier to write, debug and understand

• This is the focus of this course

• Examples

– compute the interest for six months of Mr. Sachin's Savings a/c

– book a tkt. for Rahul from Mumbai to Bangalore

– Switch on the alarm when belt not fastened

Translators/Compilers

• High level programs can not run directly on computers

• need to be translated to low level instructions

• compilers do this job

• compilers are themselves programs - system programs

• CS students learn how to write compiler software

Operating Systems

• Compilers alone are not enough

• Other programs required for executing application programs – Operating Systems

• Provides a high level view of hardware

• Efficient utilization of resources

• various utility functions, like reading inputs, printing, etc.

• UNIX, Windows, SunOS, Solaris,

• GNU/Linux

A Simplified Picture

OS is the boss

• OS gateway to the machine

• All interaction through the OS

• OS is in control always

• Safety, Security and Efficiency

• Watches for inputs (mouse,keyboard) and provides appropriate responses

– Giving login Prompts,

– Reading user name and passwords

– Allows or rejects

• Runs the command line interpreter (window manager)

The Shell

• The command line interface is called shell

• Various versions of shell

– C-shell, Bash, etc.

• After login, user commands are interpreted by the shell and appropriate OS commands are executed

• User commands to create/remove, edit files, compile and execute programs etc.

• When a user command is executed, there is a momentary transfer of control

• After execution, control is transferred back

Programming Languages

• Program instructions should be precise enough to be understood by machines or other programs

• Compilers and Raw HW are dumb

• need precise syntactic rules and a unique semantics

• Programming languages define these rules and semantics

• Hundreds of languages - FORTRAN, Algol 60, PASCAL, BASIC, C, C++, Java,

Fortran

• We teach FORTRAN

• First High Level Language (1954 – 57)

• John Bachus (IBM), got Turing Award

• Revolutionary Step

• Grand father of all modern PL

• Name derived from Formula translation

• Simple idea: Mathematical formulae are high level descriptions of computations

Evolution of Fortran

• Original Fortran very primitive, restrictive and small

• It has evolved over the years

– Fortran II

– Fortran IV

– Fortran 66, Fortran 77

– Fortran 90, Fortran 95

• Fortran 90 compares with all modern languages

• We will use FORTRAN 90

• So, this is a course on Programming in Fortran 90

Why Fortran

• Efficient compilers exist

• Oldest and widely used

• Large base of utilities and programs

• It has all modern features

• Fortran 90 is just a choice

• Self-learning of Programming in C, Java or any PL possible after this

Main Focus

• Problem solving using computers

• Fortran for concreteness

• Exercises in programming in a HLL

• All languages, at your level, are equivalent

• Obtaining a solution is more difficult

• Representing solution in a PL require mastery over the language and comes with practice