This document will explain the purpose and usage of compilers as well as provide links to well-known Pascal compilers. If you are already familiar with what compilers are, you can skip to the Free Pascal download section.

When talking about computer languages, there are basically three major terms that will be used.

1. Machine language -- actual binary code that gives basic instructions to the computer's CPU. These are usually very simple commands like adding two numbers or moving data from one memory location to another.
2. Assembly language -- a way for humans to program computers directly without memorizing strings of binary numbers. There is a one-to-one correspondance with machine code. For example, in Intel x86 machine language, ADD and MOV are mnemonics for the addition and move operations.
3. High-level language -- permits humans to write complex programs without going step-by step. High-level languages include Pascal, C, C++, FORTRAN, Java, BASIC, and many more. One command in a high-level language, like writing a string to a file, may translate to dozens or even hundreds of machine language instructions.

All computers can only run machine language programs directly. Assembly language programs are assembled, or translated into machine language. Likewise, programs written in high-level languages, like Pascal, must also be translated into machine language before they can be run. The technical terminology for this operation is compiling.

The program that accomplishes the translation is called a compiler. This program is rather complex since it not only creates machine language instructions from lines of code, but often also optimizes the code to run faster, adds error-correction code, and links the code with subroutines stored elsewhere. For example, when you tell the computer to print something to the screen, the compiler translates this as a call to a pre-written module. Your code must then be linked to the code that the compiler manufacturer provides before an executable program results.

With high-level languages, there are again three terms to remember:

1. Source code -- the code that you write. This typically has an extension that indicates the language used. For example, Pascal source code usually ends in ".PAS" and C++ code usually ends in ".CPP"
2. Object code -- the result of compiling. Object code usually includes only one module of a program, and cannot be run yet since it is incomplete. On DOS/Windows systems, this usually has an extension of ".OBJ"
3. Executable code -- the end result. All the object code modules necessary for a program to function are linked together. On DOS/Windows systems, this usually has an extension of ".EXE"

The de facto standard in compilers is Borland Pascal. A long time ago, most Pascal compilers were clumsy and slow, strayed far from the Pascal standard, and cost several hundred dollars. In 1984, Borland introduced Turbo Pascal, which sold for less than $100. This product was an instant success. However, in 1993, the last version of Turbo Pascal, version 7 for DOS, came out. After that, the demand for DOS programs plummetted and Borland (now renamed Inprise) focused on producing Windows compilers.

This tutorial will only deal with console-based programming, where the computer prints lines of data to the screen and the user interact with the program using a keyboard. The goal of the tutorial is to teach how to program in Pascal. Once you've learned that, you can easily look at a reference book or another web page and pick up graphics and windowing systems on your own. Thus, old version of Borland Pascal will work fine. For example, you can visit the Borland Museum to download an old copy of Borland Pascal. The latest free version available is 5.5.

Because of Borland's dominance in the market, there are few other commercial Pascal compilers for DOS/Windows computers. There, are however, some shareware and freeware compilers. Check The Open Directory category on Pascal Compilers for more information.

For non-DOS computers, there are also very few commercial compilers. Metrowerks, until very recently, supported Pascal in its flagship product for Macintosh computers, Metrowerks Codewarrior. However, Codewarrior now concentrates on C, C++, and Java. If you have a Macintosh computer, you can grab an old copy of Symantec Think Pascal, which is about as old as Borland Pascal (as seen by the fact that it produces 68k code rather than PowerPC code). See The Free Country's Free Pascal Compiler List for more information.

Several varieties of UNIX, including Linux, include C, C++, FORTRAN, and Pascal compilers. The Pascal compiler on UNIX is generally named "pc." This will be good enough for you to learn Pascal with, but it is very limited in terms of power and you will quickly outgrow it.

The open-source revolution started with Linux has yielded a superb free Pascal compiler as well. This compiler has versions for the Linux, DOS, OS/2, Win32, and Amiga platforms. Free Pascal is mostly compatible with Borland Pascal in syntax, and is much more useful since you can take your code to so many different platforms.

Useful pages at the Free Pascal site:

• Home page
• Download Free Pascal

I suggest downloading the compiler in one big package unless you pay for timed Internet access. This takes a while, but it has the virtue of making it very simple to install and giving you all the parts of the compiler, including optional example code.

Installation is relatively straightforward. For DOS, OS/2, and Windows, simply unZIP the ZIP file that you downloaded and run the INSTALL program. For Linux, if you downloaded the big package, you can also simply run INSTALL. If you downloaded the Red Hat or Debian packages, you'll need to run your Linux distribution's package manager. If you got the tarball, you'll need to compile the compiler yourself. As for Amiga, the number of Amigas out there is very small, limited mostly to Amiga enthusiasts, since no Amigas have been built in about a decade. If you're an Amiga enthusiast, chances are you know a lot about computers already and don't need any help to install the compiler.

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