What's this DLL (or EXE)?

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Summary: It's often difficult given just a DLL to know exactly where it came from or what it does. We'll look at a few steps you can take to try to find out.

You've got a problem with a DLL. Maybe it's missing; maybe it's causing an application to crash, or maybe you've just found it in an unlikely spot. The problem is that you have no idea what it is!

Here are some steps ranging from easy to obscure to help track down just what the DLL is going on. This approach actually works for EXE's and many other types of files if you're trying to track one of those down.

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• File location: I know it's obvious but it needed to be said. If the directory you've found the DLL in called "Leo's Application", then chances are the DLL is some component of Leo's Application. Unfortunately that doesn't always work for directories that are common, such as any of the Windows directories. Lots of applications throw DLLs into the Windows tree.

• File Version Information: Most DLLs and EXEs now have version information embedded in them. The easiest way to see the version information is to, in Windows Explorer, right click on the file, select properties, and then select the "Version" tab. There you'll see any version information that the developer has supplied.

  The problem is that not all DLLs or EXEs may have version information, and in those that do, the description of the DLL may be vague. The version information for VER.DLL shows "Version Checking and File Installation Libraries", but the description for CSSeqChk.dll will tell you "CSSeqChk" - not nearly as informative. (Though if you look at the "Product Name" portion of the version info it will at least tell you "Complex Scripts Sequence Check" - still not very helpful, but at least the author made an attempt.)

• The Manufacturer's Web Site: the version info might at least give you the company that created the DLL. Different companies offer different levels of on-line functionality, so it's hard to enumerate what to expect here, but searching the company's support site might well take you to very specific information about the file in question.

• Microsoft's DLL Help Database: Since so many of the DLLs on a Windows machine are from Microsoft this little known DLL Help Database is the next line of inquiry. It's a nifty source for determining what product(s) shipped a given DLL. It also contains a version history as well, showing which version of each DLL shipped with each version of a product. If we plug in CSSeqChk.dll we'll find that there are currently three versions listed, and by examining the "more information" available for each, we'll see that they ship as part of Internet Explorer 6 - either standalone or as part of a product such as recent versions of Visual Studio .NET or Windows.

• Microsoft's Knowledgebase: Even if the DLL isn't from Microsoft it's still worth searching the Knowledgebase, especially if the DLL is causing your system problems. Quite often a knowledgebase article will reference third party DLLs and describe issues and/or resolutions. A search for "CSSeqChk.dll" confirms it as part of Internet Explorer, as the search results are all file listings for IE distributions.

• Google: You probably already know how powerful Google can be. Search on the DLL name and you will likely get a number of hits. This is where it gets interesting and takes a little work. Many of the hits will simply be file lists, much like we just found in Microsoft's Knowledgebase. Others will be from questionable sources that claim to be able to provide you with copies of just about any DLL (not only are most of these overseas, but the practice violates copyright, and is just fundamentally too scary to trust). However in amongst the "noise" will often be interesting discussions or even Q&A - not unlike the text you're reading - that might well mention and provide more information on the DLL.

  In one sense using Google is a long shot, and you'll need to spend some time separating the wheat from the chaff. A Google search for our example CSSeqChk.dll displays 25 hits, only the last of which a discussion in a Dell support forum actually relates it in a readable fashion back to Internet Explorer, as we'd already determined. On the other hand, it can be quite educational to read through some of the interesting material that results.