Sometimes we need determine when a windows version is a server edition (2000, 2003 or 2008) or a Desktop edition. to do this we can use the VerifyVersionInfo function. this function compares a set of operating system version requirements to the corresponding values for the currently running version of the system.

but exist a problem, the version of this function declared in the Windows unit uses a OSVERSIONINFO parameter.

function VerifyVersionInfo(var lpVersionInformation: TOSVersionInfo;
  dwTypeMask: DWORD; dwlConditionMask: DWORDLONG): BOOL; stdcall; 

And in this case we need pass a OSVERSIONINFOEX Structure, so we must re-declare this function in this way.

{$IFDEF UNICODE}
function VerifyVersionInfo(var LPOSVERSIONINFOEX : OSVERSIONINFOEX;dwTypeMask: DWORD;dwlConditionMask: int64): BOOL; stdcall; external kernel32 name 'VerifyVersionInfoW';
{$ELSE}
function VerifyVersionInfo(var LPOSVERSIONINFOEX : OSVERSIONINFOEX;dwTypeMask: DWORD;dwlConditionMask: int64): BOOL; stdcall; external kernel32 name 'VerifyVersionInfoA';
{$ENDIF}

Now to work with the VerifyVersionInfo function we need establish the requirements to check .

   ZeroMemory(@osvi, sizeof(OSVERSIONINFOEX));
   osvi.dwOSVersionInfoSize := sizeof(OSVERSIONINFOEX);
   osvi.dwMajorVersion := 5; //at least windows 2000
   osvi.dwMinorVersion := 0;
   osvi.wServicePackMajor := 0;
   osvi.wServicePackMinor := 0;
   osvi.wProductType := VER_NT_SERVER; // Check windows server edition

then we need set the flags to interrogate the VerifyVersionInfo function using the VerSetConditionMask function

   op:=VER_GREATER_EQUAL;
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_MAJORVERSION, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_MINORVERSION, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_SERVICEPACKMAJOR, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_SERVICEPACKMINOR, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_PRODUCT_TYPE, VER_EQUAL );

and finally call the function in this way

   VerifyVersionInfo(osvi,VER_MAJORVERSION OR VER_MINORVERSION OR
      VER_SERVICEPACKMAJOR OR VER_SERVICEPACKMINOR OR VER_PRODUCT_TYPE, dwlConditionMask);

This is the source code of the demo console application.

program ISWindowsServer;

{$APPTYPE CONSOLE}

uses
  Windows,
  SysUtils;

{$IFDEF UNICODE}
function VerifyVersionInfo(var LPOSVERSIONINFOEX : OSVERSIONINFOEX;dwTypeMask: DWORD;dwlConditionMask: int64): BOOL; stdcall; external kernel32 name 'VerifyVersionInfoW';
{$ELSE}
function VerifyVersionInfo(var LPOSVERSIONINFOEX : OSVERSIONINFOEX;dwTypeMask: DWORD;dwlConditionMask: int64): BOOL; stdcall; external kernel32 name 'VerifyVersionInfoA';
{$ENDIF}
function VerSetConditionMask(dwlConditionMask: int64;dwTypeBitMask: DWORD; dwConditionMask: Byte): int64; stdcall; external kernel32;

function IsWinServer : Boolean;
const
   VER_NT_SERVER      = $0000003;
   VER_EQUAL          = 1;
   VER_GREATER_EQUAL  = 3;
var
   osvi             : OSVERSIONINFOEX;
   dwlConditionMask : DWORDLONG;
   op               : Integer;
begin
   dwlConditionMask := 0;
   op:=VER_GREATER_EQUAL;

   ZeroMemory(@osvi, sizeof(OSVERSIONINFOEX));
   osvi.dwOSVersionInfoSize := sizeof(OSVERSIONINFOEX);
   osvi.dwMajorVersion := 5;
   osvi.dwMinorVersion := 0;
   osvi.wServicePackMajor := 0;
   osvi.wServicePackMinor := 0;
   osvi.wProductType := VER_NT_SERVER;

   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_MAJORVERSION, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_MINORVERSION, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_SERVICEPACKMAJOR, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_SERVICEPACKMINOR, op );
   dwlConditionMask:=VerSetConditionMask( dwlConditionMask, VER_PRODUCT_TYPE, VER_EQUAL );

   Result:=VerifyVersionInfo(osvi,VER_MAJORVERSION OR VER_MINORVERSION OR
      VER_SERVICEPACKMAJOR OR VER_SERVICEPACKMINOR OR VER_PRODUCT_TYPE, dwlConditionMask);
end;

const
WindowsEditionStr : array [boolean] of string = ('Desktop','Server');

begin
  try
    Writeln( Format('Running in Windows %s edition',[WindowsEditionStr[IsWinServer]]));
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  readln;
end.