How to get computer name ?

function GetComputerName: string;
var
  buffer: array[0..MAX_COMPUTERNAME_LENGTH + 1] of Char;
  Size: Cardinal;
begin
  Size := MAX_COMPUTERNAME_LENGTH + 1;
  Windows.GetComputerName(@buffer, Size);
  Result := StrPas(buffer);
end;

example usage : 

procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit1.Text := GetComputerName;
end;