system> (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)