This article was previously published under Q72113
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To give the user quick response and a full set of MS-DOS Shell features,two files are used, DOSSHELL.COM and DOSSHELL.EXE.
When MS-DOS finds an .EXE and .COM file with the same name, the .COM filetakes precedence. The .COM file is a subset of the .EXE file. A .COM filecontains only a single segment for its code and data, so it can be quicklyloaded. The .EXE file, however, may contain many code and data segments, soit takes more time to load. The DOSSHELL.EXE program will not fit into aCOM file's single 64K segment.
The DOSSHELL.COM file is the resident part of MS-DOS Shell. It is notabsolutely necessary to use the DOSSHELL.COM, because the same code iscontained in DOSSHELL.EXE, but using DOSSHELL.COM speeds up the load time.When you execute the DOSSHELL command at the MS-DOS prompt, theDOSSHELL.COM file gets executed first and then the DOSSHELL.COM file callsthe DOSSHELL.EXE file. If the DOSSHELL.COM file does not exist,DOSSHELL.EXE is executed. Finally, when you execute the DOSSHELL.COM file,you can save about 16 bytes of memory.
For more information, query on the following words here in the MicrosoftKnowledge Base:
ms-dos and <version number> and dosshell
where <version number> is the MS-DOS version you are using; for example,5.00.