Junk and Obsolete Files
*.~*, ~*.*, *.*~, *.---, *.tmp, *._mp, *._mp
These file types are all indicative of standard Windows temporary files.  These are the files that are created by applications when they are running, and are supposed to be removed when they close.  Most of the time, these types of files are used as virtual memory undo information.
*.old, *.bak, *.syd
These files are indicative of backup copies automatically created by installation programs that needed to modify an existing configuration / system file, such as autoexec.bat or config.sys.  These files are usually initially created to allow you a way to "roll-back" to your original settings should the new configuration cause problems.  If your system is running ok, there is no reason to keep these files.
*.chk
When you use ScanDisk and it finds errors or lost clusters on your hard drive, you have the option to save this information as a raw file with a .chk extension.  These files are only necessary if you have lost some type of information and are attempting to find or extract it from your hard drive (a very difficult and expensive process).  If  your system is currently running ok, there is no reason to keep these files if they exist.
*.gid
When you open a Windows help file and select the tab labeled "Search", the help system builds a search index with the extension of .gid.  These files usually consume a great deal of space and can also be automatically re-generated if you ever need to search within the help file again, so there is little reason to keep them resident on your system if you attempting to conserve drive space.
mscreate.dir
"mscreate.dir" files are temporarily created in many "common" application folders for indexing purposes.  Sometimes these files are left behind and become obsolete when you uninstall or manually remove various files from your system.  When these "mscreate.dir" files are created, they are marked as "read-only" (a file that is "read-only" is meant to be accessed and read from, but not moved or deleted).  Although these files are marked as "read-only", they may safely be removed from your system if desired, as they are dynamically re-created when and if an application needs to access them again for indexing purposes.
0???????.nch
When you access newsgroups on the Internet using programs such as Microsoft’s Outlook Express™ much of the information is downloaded locally to your hard drive and stored as "cache" in a file with the extension .nch, enumerated using a set of 9 numbers.  Since Internet newsgroup information is most often extremely extensive,  this information, when saved to a file, can add up to tens, if not hundreds, of megabytes of disk space over time.  Because Internet newsgroup information is also constantly changing and these files are readily available again for downloading when necessary, it may be a good idea to remove them periodically when drive space conservation is a priority.
*.dmp
When a critical error occurs in Windows the operating system can be instructed to automatically save the contents of memory to disk in order to allow a system administrator (or someone with equivalent knowledge) to analyze the system’s state prior to the error.  The files that contain this information have the extension ".dmp", and are usually extremely large (ranging from several megabytes up to multiple gigabytes, depending on the state of your system at the time of the error).  These files will remain on your system until manually removed, and unless they are needed for analysis purposes, a great deal of space can be preserved by regularly removing them.
How do I know that the files I scan for are safe to remove?
Although we strongly recommend a full system backup before performing any removal operation on your system, you can be fairly certain that the files that this tool finds are completely safe to remove.  We have spent years researching the subject of temporary files and obsolete data stored by Windows operating systems and have compiled a list of very reliable file types that may be assumed to be "junk or obsolete".  The files that this tool looks for are by their very nature intended to be removed anyway, yet for some reason were not.  There are various options available as well to ensure that the files found are not being used and/or have not been used recently by any applications.