What is R8139n51?

R8139n51.SYS is a Windows driver. A driver is a small software program that allows your computer to communicate with hardware or connected devices. This means that a driver has direct access to the internals of the operating system, hardware etc. The free file information forum can help you determine if R8139n51.SYS is a Windows system file or if it belongs to an application that you can trust.

Run a free scan to check for R8139n51 drivers in need of updating

R8139n51.SYS file information

The process known as Realtek RTL8139/810x Family NDIS (version 5.1 Drv) or Realtek RTL8139/810X Family NDIS (version 5.1 Drv) or CNet FAST200 NDIS (version 5.1 Driver)

belongs to software Realtek RTL8139/810x Family Fast Ethernet NIC NT Driver or Realtek RTL8139/810X Family Fast Ethernet NIC NT Driver or CNet FAST200 PCI Fast Ethernet Adapter NT Driver

by Realtek Semiconductor ( or CNet Technology.

Description: R8139n51.SYS is not essential for the Windows OS and causes relatively few problems. The R8139n51.SYS file is located in the C:\Windows\System32\drivers folder. Known file sizes on Windows 10/8/7/XP are 45,568 bytes (37% of all occurrences), 46,976 bytes or 45,312 bytes. 
The driver can be started or stopped from Services in the Control Panel or by other programs. The program is not visible. There is no detailed description of this service. It is not a Windows core file. The R8139n51.SYS file is a trustworthy file from Microsoft. R8139n51.SYS appears to be a compressed file. Therefore the technical security rating is 14% dangerous, however you should also read the user reviews.

Recommended: Identify R8139n51.SYS related errors

Important: Some malware disguises itself as R8139n51.SYS, particularly when not located in the C:\Windows\System32\drivers folder. Therefore, you should check the R8139n51.SYS process on your PC to see if it is a threat. We recommend Security Task Manager for verifying your computer's security. This was one of the Top Download Picks of The Washington Post and PC World.


User Comments

It's for use with Realtek 8139 compatible cards
Ist ein treiber für die Netzwerkkarte (Realteak)
  Mayer Benjamin  

Summary: Average user rating of R8139n51.SYS: based on 2 votes with 2 user comments. One user thinks R8139n51.SYS is essential for Windows or an installed application. One user thinks it's probably harmless.

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Best practices for resolving R8139n51 issues

A clean and tidy computer is the key requirement for avoiding problems with R8139n51. This means running a scan for malware, cleaning your hard drive using cleanmgr and sfc /scannow, uninstalling programs that you no longer need, checking for Autostart programs (using msconfig) and enabling Windows' Automatic Update. Always remember to perform periodic backups, or at least to set restore points.

Should you experience an actual problem, try to recall the last thing you did, or the last thing you installed before the problem appeared for the first time. Use the resmon command to identify the processes that are causing your problem. Even for serious problems, rather than reinstalling Windows, you are better off repairing of your installation or, for Windows 8 and later versions, executing the DISM.exe /Online /Cleanup-image /Restorehealth command. This allows you to repair the operating system without losing data.

To help you analyze the R8139n51.SYS process on your computer, the following programs have proven to be helpful: Security Task Manager displays all running Windows tasks, including embedded hidden processes, such as keyboard and browser monitoring or Autostart entries. A unique security risk rating indicates the likelihood of the process being potential spyware, malware or a Trojan. Malwarebytes Anti-Malware detects and removes sleeping spyware, adware, Trojans, keyloggers, malware and trackers from your hard drive.

Other processes

R8139n51.SYS [all]