Some PDP-11 info (was Re: C compilers for RSTS/E?)

Jerome Fine replies: I am not sure if that is a benefit. Since my wife used to refer to the terminals for the PDP-11 systems (VT100, etc.) as the actual computers and could not even tell or understand what a hard disk drive was, there was obviously no meeting of the minds as far as work was concerned. BUT, when we met and were married (1957) BEFORE any real computers were widely known and understood, neither of us could even recognize a computer. I did not meet my first computer until about 1958 at an insurance company during a summer job. Probably a BRIEF outline of RT-11 file structures: (a) Home block in block 1 which contains non-essential Volume ID. (b) Directory segments of 2 blocks each (maximum of 31) start in block 6 (c) First 5 words of each directory segment: - Maximum number of directory segments - Next directory segment number (0 if end of chain) - Highest number of directory segments - Extra number of bytes for each directory entry - Start block number of directory entries for THIS directory segment (d) Standard file entries contain 7 words - Status word for the directory entry - 3 words of Radix50 (2 for file name, 1 for file type) - Number of blocks for this directory entry (0 to 65535 blocks) - Spare word used for a Tentative File Entry - word for Creation Date Agreed that version numbers were NOT possible ONLY File Creation Date (NO File Creation Time), let alone other file parameters Files could be PROTECTED against being DELETED; DEC NEVER had code to allow files to be RO (Read ONLY). The RT-11 command: [UN]PROTECT FOOBAR TSX-PLUS used the extra word as the (Creation Time/3) for each file in seconds/3 AFTER the file was made permanent. The extra bytes allowed for each file entry can be used to hold any data for each file such as Reference Date/Time, Modification Date/Time, Backup Date/Time. Some privately used systems have a modified USR which supports such enhancements. Starting with V05.00 in 1983, DEC supported the LD(X).SYS device drivers (Logical Disks) which allowed the RT-11 command: MOUNT LDn: DEV:FOOBAR.DSK after which LDn: could be used as a normal data disk, including having its own file directory. Thus, the single file directory for the primary physical hard disk drive (maximum size of 65536 blocks) can hold hundreds (normally only a dozen at most) of files which can also be used a logical devices (normally 8 at one time - can be extended to 64 at one time with a SYSGEN). These words were NOT supported by DEC. I understand that Dibol programs may have used them. Does your wife remember and if so, how were they used? YES - that aspect was a bit inconvenient, but not really difficult. The big problem was that a file could NOT be expanded in size unless the space immediately following the file was empty and had the number of blocks that were required. This almost never caused a problem. It was what RT-11 users expected, if they even thought about it at all. This was a problem at times, especially for those RT-11 users who did not pay attention to fragmentation in the disk space. NOT a problem at all if the users were aware of the problem. HOWEVER, for myself, I would ALWAYS make a backup copy of a hard disk before doing this since any failure would be catastrophic. But most RT-11 users ignored the possibility and on rare occasions lost many files. What did she do?????? By the time I worked on a PDP-11/34 in 1979, my wife and I had been married for 22 years and I was no longer the geek. Anyone who can type quickly does not have a problem. The commands are a bit stark, but no more difficult to remember than DCL (DEC COMMAND LANGUAGE). Why was the /S switch important in Dibol????? These days, the equivalent command for DUP stops the user from using the <CTRL/C> until the squeeze is finished. Actually, the <CTRL/C> (^C) is part of RT-11. The program can disable the feature when it requests to do so (providing the user does not crash RT-11 during a window when RT-11 is vulnerable due to an RT-11 bug). If the <CTRL/C> is enabled, then RT-11 kills execution. As stated above, DUP (which now performs the squeeze) has <CTRL/C> DISABLED while the squeeze is in progress. While I agree that early RT-11 systems had severe limitations, eventually RT-11 evolved into a rich operating system, especially when TSX-PLUS became available (actually a complete rewrite of the resident portion of the operating system by S&H) which supported multi-job and even multi-task usage. It was actually called a poor man's VMS since even security was very strong for the early 1980s. Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.