What is Fastfat?

Fastfat.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 Fastfat.sys is a Windows system file or if it belongs to an application that you can trust.

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

Fastfat.sys file information

The process known as Fast FAT File System Driver belongs to software Microsoft Windows Operating System by Microsoft (

Description: The original Fastfat.sys is an important part of Windows and rarely causes problems. Fastfat.sys is located in the C:\Windows\System32\drivers folder. Known file sizes on Windows 10/8/7/XP are 143,744 bytes (51% of all occurrences), 143,360 bytes or 145,152 bytes. 
The driver can be started or stopped from Services in the Control Panel or by other programs. The file is a Windows system file. The program is not visible. There is no detailed description of this service. The Fastfat.sys file is a Microsoft signed file. Fastfat.sys appears to be a compressed file. Therefore the technical security rating is 0% dangerous, however you should also read the user reviews.

Recommended: Identify Fastfat.sys related errors

Important: Some malware disguises itself as Fastfat.sys, particularly when not located in the C:\Windows\System32\drivers folder. Therefore, you should check the Fastfat.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

file used in raid or scsi setups in Microsoft OS's
  James Urwiller, Service Manager Computer Warehouse #4   (further information)
I deleted fastfat.sys off my laptop and now everytime i plug in a protable drive or digital camera it prompts me to format the external drive.
When not loaded, cannot read from a floppy or USB memory stick.
when i tried installing windows after a fat32 format i get tis sot error i.e. STOP:0X00000050 ( 0XA11B7A4C,0X00000000,0XFC795AD6,0X00000002 ) fastfat.sys-Address FCF9AD6 base at FC&8D000 DateStamp 41107EB7
This is the driver for reading/writing FAT formatted drives (usually USB sticks, smaller external drives, and those devices appearing as drives such as digital cameras and mp3 players)
  Tim, Senior Electrical Engineer  
needed to mount FAT-based drives (USB sticks, floppy/tape drives)
I have a customer of mine with multiple infections. According to one of my Infectious Removal Tools C:\WINDOW\System32\dllcache/fastfat.sys is an infection.
  PC Recovery Technician.  
Essential for USB Sticks, when crash occurs at boot, remove all USB storage devices
Used by TrueCrypt when encrypted volumes are formatted with FAT. Also used, as others have said, for other FAT-formatted volumes.
  IT Fixt  
FAT kernel-level file system driver loaded via IFS for Windows NT 4.x upwards
  Some Nerd   (further information)

Rating chart

Summary: Average user rating of Fastfat.sys: based on 16 votes with 10 user comments. 13 users think Fastfat.sys is essential for Windows or an installed application. One user thinks it's probably harmless. One user suspects danger. One user thinks Fastfat.sys is dangerous and recommends removing it. One user is not sure about it.

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Best practices for resolving Fastfat issues

A clean and tidy computer is the key requirement for avoiding problems with Fastfat. This means running a scan for malware, cleaning your hard drive using 1cleanmgr and 2sfc /scannow, 3uninstalling programs that you no longer need, checking for Autostart programs (using 4msconfig) and enabling Windows' 5Automatic 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 6resmon 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 7DISM.exe /Online /Cleanup-image /Restorehealth command. This allows you to repair the operating system without losing data.

To help you analyze the Fastfat.sys process on your computer, the following programs have proven to be helpful: ASecurity 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. BMalwarebytes Anti-Malware detects and removes sleeping spyware, adware, Trojans, keyloggers, malware and trackers from your hard drive.

Other processes

Fastfat.sys [all]