This fixed size, which could not be increased without breaking application compatibility, led to the FCB's eventual demise as the standard method of accessing files.
Some preceding "negative offset" bytes were squeezed from reserved spaces in CP/M Zero Page and DOS Program Segment Prefix for storing file attributes.
[1][3][4] When, with MS-DOS 2, preparations were made to support multiple processes or users,[3][4] use other filesystems[3][4] than FAT or to share files[4] over networks in the future, FCBs were felt to be too small to handle the extra data required for such features[4] and therefore FCBs were seen as inadequate for various future expansion paths.
This has the great advantage that these structures can grow in size in later operating system versions without breaking compatibility with application programs; its disadvantage is that, given the rather simplistic memory management of DOS, space for as many of these structures as the most "file-hungry" program is likely to use has to be reserved at boot time and cannot be used for any other purpose while the computer is running.
Under DR-DOS, both FILES and FCBS come from the same internal pool of available handles structures and are assigned dynamically as needed.
Every DOS executable started from the shell (COMMAND.COM) was provided with a pre-filled 256-byte long data structure called the Program Segment Prefix (PSP).
The initial address for the DTA was set to overlay the area in the PSP (at address 0x80) where the command line arguments were stored, such that a program needed to parse this area for command line arguments before invoking DOS functions that made use of the DTA (such as reading in a file record), unless the program took care to change the address of the DTA to some other memory region (or not use the DTA/FCB functions altogether, which soon became deprecated in favour of file handles).