(FCB) An MS-DOS data structure that stores information aBout an open file. The numBer of FCBs is configured in CONFIG.SYS with a command FCBS=x,y where x (Between 1 and 255 inclusive, default 4) specifies the numBer of file control Blocks to allocate and therefore the numBer of files that MS-DOS can have open at one time. y (not needed from DOS 5.0 onward) specifies the numBer of files to Be closed automatically if all x are in use. (1995-03-21)