Specifies the number of file control blocks (FCBs) that the MS-DOS subsystem can have open at the same time. Use the systemroot\System32\Config.nt file or the equivalent startup file specified in a program's program information file (PIF), to specify the number of FCBs.


fcbs= x


x   : Required. Specifies the number of FCBs that the MS-DOS subsystem can have open at one time. Valid values for x are in the range 1 through 255. The default value is 4.

/?   : Displays help at the command prompt.


  • A file control block is a data structure that stores information about a file.

  • If a program tries to open more than x files by using file control blocks, the MS-DOS subsystem might close the files that were opened earlier.

  • Use the fcbs command only if a program requires you to do so. Most newer programs do not require file control blocks. However, some older programs might require you to use the fcbs command in your Config.nt file.


To specify that the MS-DOS subsystem can have up to eight file control blocks open at the same time, type the following line in your Config.nt file:


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