sequential file, and use that reference to jump to that specific location again. Sequential files are somewhat more efficient in terms of space than line files and can be more efficient in terms of CPU time too when compared with large disorganized line files. But the main reason for the existence of SEQ files is that they supported long lines (up to 32,767 characters) before line files did. Sequential files were less common once line files could support long lines. Sequential files are also used to force new lines to be appended to the end of the file without the need to give the line number range (LAST+1). Sequential with line number files Sequential With Line Number files ($CREATE name TYPE=SEQWL) are similar to Sequential Files, except that their line numbers were explicitly stored. They have all the restrictions of Sequential Files, except that the line number could be specifically supplied when writing to a file (as long as it is greater than the last line number written to the file). Unlike Line Files, the first read of an SEQWL file returns the first line of the file, even if it was negative. SEQWL files were rarely used, and were not officially supported or were removed from the documentation by some MTS sites. Because line files did not work well with the Data Cell, SEQWL files were implemented as a way to allow the Data Cell to be used for longer term less expensive storage of files while still preserving line numbers. Shared files Over time the sharing of files between MTS users evolved in four stages. Stage one allowed for limited file sharing, where public or library files (files whose names start with an asterisk) were readable by all users and all other files (user files) could only be accessed by their owners. Public files were owned and maintained by Computing Center staff members, so at this stage only Computing Center files were shared. Stage two allowed for limited file sharing, where the program *PERMIT could be used to (i) make a file read-only (RO) to the file's owner and all other MTS users, (ii) make a file available for copying by members of the same project as the file's owner using the program *COPY, or (iii) make a file available for copying by all other users using the program *COPY. As for stage one, by default owners had