sdm7g@dale.acc.Virginia.EDU (Steve D. Majewski) (09/27/90)
As far as I have been able to decipher, VAX/VMS RMS leaves ONE byte in the file header that can be user defined. ( I believe it is FH1$B_USERCHAR, but it's been a while since I poked around. ) 1) Is this still "reserved for users" , or has DEC taken it back to reserve for something else? 2) Has anyone out there actually tried to use it for anything ? [ What I had in mind, once, long ago, was modifying the I/O to ] [ do auto-magic file compression/decompression: If the right bit ] [ in FH1$B_USERCHAR is set, then the first item in the file is ] [ the decompression map :: decompress and unblock the records ] [ on reads. This obviously would entail re-vectoring SYS$OPEN, ] [ SYS$READ, SYS$GET, etc. Other info that could tag along ] [ could be audit trails, file comments, etc., the idea being that ] [ the extra data would be invisible to "normal" reads, and the ] [ files still compatable with their applications. ] [ The necessity of doing this on VMS has passes, as we are moving ] [ more applications over to UNIX, but I am still curious about ] [ whether my original notion was practical. And I am interested ] [ in comparing the difficulty of the same project in VMS vs UNIX. ] 3) Has DEC ever published anything on RMS/ODS/File&I/O systems as exhaustive as the black book on VMS internals? Or anything ? If you reply via E-mail, I will summarize and post. - Steve Majewski sdm7g@virginia.edu ======================================================================== Steven D. Majewski University of Virginia Physiology Dept. sdm7g@Virginia.EDU Box 449 Health Sciences Center (804)-982-0831 Charlottesville, VA 22908