.sys is a
filename extension
A filename extension, file name extension or file extension is a suffix to the name of a computer file (e.g., .txt, .docx, .md). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically ...
used in MS-DOS applications and
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may al ...
s. They are system files that contain
device drivers or hardware configurations for the system.
Most DOS files are
real mode
Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. The mode gets its name from the fact that addresses in real mode always correspond to real locations in memory. Real mode is characterized by a 20- bit ...
device driver
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ...
s.
Certain files using this extension are not, however:
*
MSDOS.SYS and
IO.SYS
is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers (hardware interfacing routines) and the DOS initialization program.
Boot sequence
In the PC bootup sequence, the first sector of the boot disk is ...
are core operating system files in
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...
and
Windows 9x
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in sub ...
.
*
CONFIG.SYS is a
text file
A text file (sometimes spelled textfile; an old alternative name is flatfile) is a kind of computer file that is structured as a sequence of lines of electronic text. A text file exists stored as data within a computer file system. In opera ...
that contains various configuration options and specifies what device drivers will be loaded.
*
COUNTRY.SYS is a
binary database containing country and codepage related information for use with the CONFIG.SYS
COUNTRY directive and the
NLSFUNC driver.
*
KEYBOARD.SYS is a binary database containing keyboard layout related information including short
P-code sequences to be executed by an interpreter inside the
KEYB
KEYB (107.9 FM, "108 Key FM") is a radio station
Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcast ...
keyboard driver.
File location
In
Windows Vista
Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...
and its successors, the .sys files are mainly found under the following paths:
:
C:\Windows\system32\drivers
:
C:\Windows\WinSxS
In
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...
, the file named
MSDOS.SYS is used to copy the system files from one drive to another, allowing the second drive to be bootable. MSDOS.SYS is located in the root directory of the bootable drive/partition (normally C:\ for hard disks) and has the hidden, read-only, and system file attributes set.
See also
*
VxD
*
Windows Driver Model In computing, the Windows Driver Model (WDM) also known at one point as the Win32 Driver Model is a framework for device drivers that was introduced with Windows 98 and Windows 2000 to replace VxD, which was used on older versions of Windows such a ...
*
Windows Driver Frameworks
*
Fat binary
A fat binary (or multiarchitecture binary) is a computer executable program or library which has been expanded (or "fattened") with code native to multiple instruction sets which can consequently be run on multiple processor types. This results ...
(for crash-protected system files)
References
sys
Executable file formats
{{Windows-stub