the PSP (see next section); this location could be changed by calling a DOS function, with subsequent file accesses implicitly using the new location. With the deprecation of the FCB method, the new file access functions which used file handles also provided a means to specify a memory buffer for file contents with every function call, such that maintaining concurrent, independent buffers (either for different files or for the same file) became much more practical. Program Segment Prefix & Program Initialisation 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). Relevant fields within this structure include: This data structure could be found at the beginning of the data segment whose address was provided by DOS at program start in the DS and ES segment registers. Besides providing the program's command line verbatim at address 0x81, DOS also tried to construct two FCB's corresponding to the first two words in the command line, the purpose being to save work for the programmer in the common case where these words were filenames to operate on. Since these FCB's remained unopened, no problem would ensue even if these command line words did not refer to files. 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). See also Record-oriented filesystem References Further reading - In-depth description of CP/M FCB CP/M technology DOS technology