Used to set the number of file control blocks (FCBs) that can be open at any time. A file control block is a data structure that stores information about a file enabling programs to access it.

The FCBS statement is only valid in Config.sys.


FCBS=x, [y]

xThe number of FCBs to be open at any time. x must be in the range 1 to 255 and the default is 4
yThe number of FCBs that cannot be closed automatically. This parameter is not required in Dos 7 and is ignored.


The use of File Control Blocks to open files is a hangover from the very early days of computing and was superseded by File Handles (see FILES) with the introduction of DOS 2. It is very unlikely that any program in use today would use File Control Blocks.

Each FCB specified requires 60 bytes of memory.

If the DOS command is used to manage the upper memory blocks (it usually is), the default values for FCBS are automatically loaded into the HMA. ie. the line
is invoked without needing to be explicitly stated. If an FCBS or FCBSHIGH statement is included in Config.sys, this will take precedence over the default values.

This page last revised:
December 9, 1999.