Understanding the Basics of Programming Languages and Processors, Slides of Geology

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Introduction

• Programming skills are not essential, but they are useful for: - Special data processing; - Customisation

Computers

• The processor (or CPU) can be thought of as the ‘heart’ of the computer as it controls the flow of information around the system.
• The processor requires instructions telling it what to do. These are provided by the operating system (OS).
• All instructions to the processor are in machine code.

Programming Languages

• Machine code can be represented as as series of binary digits (or bits ).
• Bits are normally organised in groups of 8 called bytes.
• Machine code is unintelligible to most humans, so instructions are normally provided using a language which can be translated into machine code.
• Languages can be:
  • Low level (e.g. machine code, assembley language)
  • High level

Assembley Language

• Each processor (or family of processors) has its own assembly language.
• Assembley languages provide very detailed control using mneumonics.
• It can take a lot of steps to do even simple things. For example, the following adds two single byte numbers together in 6502 assembley code.

Translation

• Irrespective of the language used, the code must be translated into machine code.
• Assembleylanguage programs are translated by an assembler.
• Machine code can also be translated in the opposite directed by a disassembler.
• High level languages are translated by either:
  • An interpreter , or
  • A compiler.

Interpreters

• Interpreters translate the source code one line at a time.
• The line is translated into machine code and executed.
• If it works, the interpreter translated the next line, and so on.
• If an interpreted program breaks down, it is fairly easy to diagnose the problem and possibly even restart the program from where it broke down.
• The main problem with interpreted languages is that they are slow.

High Level Languages

• Some high level languages are lower level than others
• C is a ‘lower’ level high level language – i.e. it gives more control and also runs faster than other high level languages, but it is more difficult to learn.
• Other high level languages (e.g. Fortran , Basic ) are easily to learn.
• Fortran is a compiled language, Basic is usually interpreted.

Platform Dependence

• Compiled executables are usually platform dependent (i.e. they are translated into the machine code used by a particular processor).
• This creates problems if you want to run programs over the internet – i.e. different users use different platforms.
• Java was developed to overcome this.
• Java compiles the source code into an intermediate byte code for distribution.
• This is then interpreted at execution by a Java Virtual Machine (JVM) for a particular platform.