A+ Certification / Beginners


The config.sys file has been around since early versions of MS-DOS. It stores modifications to the default settings that are set through msdos.sys. config.sys usually contains environment settings and device drivers load lines, for devices such as CD-ROM drives. If the file does not exist, then io.sys will apply system default settings to the environment, in addition to the settings that are found in msdos.sys. If the config.sys file does exist, io.sys ensures that after processing the config.sys file, the settings are equal to or higher than the default settings. If config.sys settings do not meet the default settings, then io.sys will apply the default settings. (Your settings may have been changed from the default settings in order to support an application; the file's value is often increased for application support.) The default entries that will be enforced are found in Table below.

Default config.sys Values
buffers=23Buffers are used when some older MS-DOS-based applications attempt to make file I/O calls. They are not used by Windows 9x or its applications.
dos=High, AutoLoads some of the command.com and msdos.sys files into the High Memory Area.
files=30Like buffers, this setting is only used by older applications. files sets the number of files that the application or command.com environment can have open simultaneously.
himem.sysHigh Memory Manager. This file gives Windows 9x access to memory above 1MB. In a round-about way, it also includes all memory above 640K.
ifshlp.sysInstallable File System Driver Helper. This driver is required to allow access to both network file systems and VFAT (the local file system).
lastdrive=ZThis gives access to drive letters up to Z:. It is only required for older applications.
settver.exeEmulates different versions of MS-DOS for compatibility with some applications.
shell=command.com /pSets the command shell to be permanent.
stacks=9,256Like buffers, this is used for compatibility with some older MS-DOS-based applications.

Windows NT can be traced back to a joint venture with IBM, and originally ran on IBM's OS/2 (Operating System 2). Since that time, Microsoft has provided some support for OS/2 applications in the Windows NT OS. This support was removed with the release of Windows XP. Windows 2000 and Windows XP do not generally use the config.sys file. If the file is edited and saved as an OS/2 text file, Windows 2000 will extract any OS/2 configuration information. This information will be written to the Registry and used for running OS/2 applications from within the Windows 2000 OS. This process happens only with Windows NT and Windows 2000 and not with MS-DOS or Windows 9x.

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