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
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Steven D. Majewski University of Virginia Physiology Dept.
sdm7g@Virginia.EDU Box 449 Health Sciences Center
(804)-982-0831 Charlottesville, VA 22908