如果安装过VS2012的话，直接打开一个VS 2012提供的控制台窗口，比如VS2012 x64 Native Tools Command Prompt.

用下面的命令查看程序的头部信息：

gdal_1.8_rtc>dumpbin /HEADERS gdal18.dll 
Microsoft (R) COFF/PE Dumper Version 11.00.60610.1 
Copyright (C) Microsoft Corporation.  All rights reserved. 
 
 
Dump of file gdal18.dll 
 
PE signature found 
 
File Type: DLL 
 
FILE HEADER VALUES 
            8664 machine (x64) 
               6 number of sections 
        52130233 time date stamp Tue Aug 20 13:44:19 2013 
               0 file pointer to symbol table 
               0 number of symbols 
              F0 size of optional header 
            2022 characteristics 
                   Executable 
                   Application can handle large (>2GB) addresses 
                   DLL 

gdal_1.8_rtc>dumpbin /HEADERS gdal18.dll
Microsoft (R) COFF/PE Dumper Version 11.00.60610.1
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file gdal18.dll

PE signature found

File Type: DLL

FILE HEADER VALUES
            8664 machine (x64)
               6 number of sections
        52130233 time date stamp Tue Aug 20 13:44:19 2013
               0 file pointer to symbol table
               0 number of symbols
              F0 size of optional header
            2022 characteristics
                   Executable
                   Application can handle large (>2GB) addresses
                   DLL

看到x64了么？ 所以这是64位的dll.