.SYS File Extension

Windows System File

Developer Microsoft
4.1  |  966 Votes

What is an SYS file?

An SYS file is a system file used by Microsoft DOS and Windows operating systems. It contains system settings and variables, and functions that are used to run the operating system. SYS files are commonly used to store device drivers and other core Windows functions.

More Information

System files are most commonly found within the C:\​Windows directory of a Windows installation. If you have Windows Vista or a later version installed the bulk of your SYS files will be located in the following directories:

  • Windows\​system32\​drivers
  • Windows\​winsxs

You may also encounter SYS files when trying to correct a device driver issue in Windows. The device driver, which is a program that enables Windows to interact with hardware, such as a keyboard, printer, or monitor, may have been deleted, become corrupt, or need to be updated.

Ideally, you should update device drivers via Windows Update to fix these issues. You can do this by selecting Settings → Update & Security → Windows Update → Check for updates → View optional updates → Driver updates.

However, you may need to manually update a device driver with an update package you downloaded from the device manufacturer's website. In this case, you can use the Device Manager included with Windows.

How do I manually update a device driver with Device Manager?

After extracting the package's contents (typically stored in a .ZIP archive) with the appropriate decompression utility, you will most likely encounter an .INF file accompanied by one or more SYS files. Follow these instructions to update the device driver with Device Manager:

  1. Open the Start menu, type "Device Manager," then open the tool.
  2. Open the branch with the hardware you need to update, then right-click the specific hardware, and select Update driver.
  3. Select "Browse my computer for drivers" and navigate to the location of the extracted update package files by clicking the Browse... button. Verify that the "Include subfolders" option is checked to make sure it can find the INF file, which stores the update instructions.
  4. Finally, click Next. Device Manager will then scan, detect, and install the extracted update package that includes the INF and SYS file(s).

NOTE: Since "sys" is short for "system," SYS files are commonly pronounced as "siss" files.

Common SYS Filenames

IO.SYS - This file stores the default DOS device drivers and the DOS initialization program. It is used by DOS and Windows 9x.

MSDOS.SYS - This file contains the core operating system code for DOS, known as the DOS kernel.

CONFIG.SYS - This file contains the primary configuration information used by DOS.

How to open an SYS file

You should not manually open SYS files since they are meant to be referenced by the Windows operating system. Modifying or deleting an SYS file may damage your system.


SYS files are typically legitimate system files used by the Windows operating system, but they may also be used for distributing and executing malware attacks on victims' computers. To protect against malicious Windows attacks, never download and install an SYS file from the Internet unless you can verify the legitimacy of the source.

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Programs that open or reference SYS files

Motorola Cell Phone Driver

Developer Motorola
3.8  |  220 Votes

A SYS file is a device driver used by a Motorola cell phone and related computer software. It allows a phone to communicate with a computer. For example, the file manager and modding tool P2KMan creates SYS files upon installation, which it uses to communicate with users' phones.

More Information

Official Motorola phone management software also creates SYS files upon installation. For example, Motorola Phone Tools (MPT) creates modem-specific SYS files that it uses to communicate with phones that use that modem.

Common SYS Filenames

M56pci.sys - SYS file used to communicate with phones that use the Motorola M56 PCI modem.

P2k.sys - SYS file created by P2KMan; used to transfer files to and from Motorola Vxxx phones.

How to open an SYS file

SYS files are not meant to be opened. Motorola phone management software loads and uses SYS files as needed.

Programs that open or reference SYS files

Motorola Phone Tools  —  Discontinued

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