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CONFIG.SYS is the configuration file for the DOS and OS/2 operating systems that specifies startup options – options that cannot be changed after the system has booted. The data it contains is read by the system and used to configure many aspects including memory management, peripherals and applications. Each line can contain a name-value pair that is either a directive that sets the value of a system setting or with name "DEVICE" extends system capability by loading a file such as a device driver or a terminate-and-stay-resident (TSR) program. CONFIG.SYS was introduced with DOS 2.0.
As Windows technology diverged from DOS over time, use of CONFIG.SYS diminished. Both CONFIG.SYS and AUTOEXEC.BAT are in the root folder of the Windows 95 and Windows 98 boot drives, but typically, they are empty. Windows Me does not use a CONFIG.SYS file at all. Instead, it loads environment variables from the Windows Registry key: HKLM\System\CurrentControlSet\Control\SessionManager\Environment.

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