http://delphi.wikia.com/wiki/CompilerVersion_Constant

The CompilerVersion constant identifies the internal version number of the Delphi compiler.

It is defined in the System unit and may be referenced either in code just as any other constant:

if CompilerVersion = 20 then
    sCompilerName := 'Delphi 2009';

or in conditional compiler expressions:

{$if CompilerVersion > 18} 
// Delphi 2007 or later 
{$endif}

The CompilerVersion constant was introduced in Delphi 6 along with conditional expressions.

In earlier Delphi versions various compiler defined VERxxx symbols are used to determine compiler versions.

CompilerVersion values and the equivalent compiler defined symbols

for the Delphi versions in which the CompilerVersion constant is defined are:

Borland Compiler Conditional Defines

http://delphi.wikia.com/wiki/Borland_Compiler_Conditional_Defines

* This conditional define is shared by the Delphi compilers

used to build C#Builder 1 and Delphi 8, which do not natively support Delphi for Win32.

This define is used in the "IDE Integration Packs" that were released to Borland partners in order to allow IDE plugins like ModelMaker Code Explorer (http://www.modelmakertools.com/code-explorer/index.html) and Castalia (http://www.delphi-expert.com/castalia3) to be compiled.

** This conditional define is shared between C++Builder 6, Delphi 6, Kylix 1, 2, and 3

(Checking for the conditional define "LINUX" helps to determine whether the compiler is

Kylix or Delphi and "BCB" can be used to determine if C++Builder is being used).

*** This conditional define is shared with C++Builder 5

**** C++Builder 3.0 used VER110 (it had its own version of the Delphi compiler included).