tail

[Dennis Lee Bieber]

On Sun, 24 Apr 2022 12:21:36 -0400, <pjfarley3 at earthlink.net> declaimed the
following:

>
>WRT the mentioned IBM utility program[me]s, the non-Posix part of the IBM mainframe file system has always provided record-managed storage since the late 1960's (as opposed to the byte-managed storage of *ix systems) so searching for line endings was (and is) irrelevant and unnecessary in that environment.  That operating system also provides basic "kernel-level" read-backwards API's for the record-managed file system, so there was never any need to build reverse-read into your code for that environment.
>

	IBM wasn't the only one... Xerox Sigma running CP/V default for text
files (those created using a text editor) used numeric ISAM keys (as record
numbers -- which is how their FORTRAN IV compiler did random access I/O
without requiring fixed length records). The system supported three access
methods: consecutive (similar to UNIX "stream" files, for files that didn't
require editing, these saved disk space as the ISAM headers could be
disposed of), the aforesaid keyed, and "random" (on this system, "random"
meant the ONLY thing the OS did was know where the file was on disk --
files had to be contiguous and pre-allocated, and what data was in the file
was strictly up to the application to manage).

	VAX/VMS had lots of different file structures managed by the RMS system
services. The default for FORTRAN text files was a segmented model, making
use of chunks of around 250 bytes [it has been years and I no longer have
the documentation] in which the start of each chunk had a code for "first
chunk", "last chunk", "intermediate chunk" (and maybe length of data in the
chunk). A record that fit completely within one chunk would have both
"first" and "last" codes set (intermediate chunks have neither code). One
had to go out of their way to create a "stream" file in DEC FORTRAN 77
(open the file with CARRIAGECONTROL=CARRIAGERETURN). Other languages on the
OS had different default file structures, but RMS would handle all of them
transparently.


-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
	wlfraed at ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/