FCBS
FCBS (File Control Blocks) is a line used in the config.sys with MS-DOS 3.1 and above to specify the number of file control blocks for file sharing. By default, MS-DOS 3 and higher the value is 4. Adding the following line to the config.sys would increase the number of stored FCBS to 5.
FCBS=5
In MS-DOS 3 and later, the FCB format is different if share.exe is being loaded.
What is an FCB (File Control Block)?
With a file system, the FCB (File Control Block) is often a 36 byte long section of a file that helps operating systems know the state of a file. FCB was used with earlier operating systems like CP/M, PC DOS, and MS-DOS 1.xx. When MS-DOS 2 was released with FAT (File Allocation Table) to help manage files, FCB began to be replaced. When FAT32 was later introduced, FCBs were no longer supported by Microsoft Windows.